Temperature and Moisture Control in Mid-Century Homes

Temperature and moisture control in mid-century houses is one of those topics that might seem less exciting and relevant until suddenly…it matters to YOU.

And while our mid-century houses have the potential be properly snug without being too sealed up. They also sometimes need a tune up. Plus a number of trendy, seemingly “esthetic” changes to your house – siding, soffit, or roof changes – can create problems that didn’t exist before. We’ll definitely cover the moisture consequences (yes, that sounds icky) of painting brick and adding vinyl siding.

So let’s dig into some building technology and the broader concept of thermodynamics so that you are READY to handle the most important considerations about moisture control in mid-century homes.

A Brief History of Home Comfort

Once people lived on the savannah, when we were hot, we took off layers. When we were cold, we put on layers, or we built a fire, we cuddled and huddled for warmth. 

Over time, we got more sophisitcated about it.

Western media often pay lots of attention to the Northern European building systems, but my German and English ancestors were pretty slow to get beyond the level of a simple roof to keep the rain off and walls to enclose us and keep us physically safe.

Thermal Comfort in Europe

Up to even just a few 100 years ago in Europe, the wealthiest of people were living in relatively uninsulated buildings where they tried to warm up certain rooms with cloth tapestries on the wall and a giant open hearth. The best place to be sitting in a situation like that was on a stone bench almost inside the fireplace, as close to the heat source as possible.

They didn’t worry about moisture because there weren’t any air barriers on those buildings. Air was always moving freely and in out right through the walls, taking moisture with it.

Other cultures solved the problems of human comfort differently (and on a different line)

Thermal comfort in Japan

In Japan they also have a cold climate winter, just like in Europe. And people there chose to insulate themselves in padded, layered clothing and then create little pockets of insulation inside of largely breezy homes.

Rather than trying to heat a whole room, you would heat the space where people physically were. So you could sit under a blanket or you could put a light heat source under a low table and then cover that whole table with a blanket so a group of people could tuck their legs underneath.  

Thermal Comfort in Korea

Not too far away, Korea took the opposite approach. A Korean traditional home in the Ondol style used a principle of heat rising to warm up a house. Ondol houses were built up over a crawl space, set on stone pillars. Then they would build a fire in a little hearth just outside the perimeter of the house and direct the heat and smoke through the crawl space where it would then circulate underneath the whole building and create a radiant floor effect. This is a 2000 year old technology, so if you compare that to Europe, they were extremely ahead of the human comfort game. 

How we approach thermal control in buildings (here) today

In the modern era, thanks to mechanical advances, we began to assume that we could separate indoor and outdoor air and create a fully sealed interior environment with perfect control of the temperature and moisture conditions. But our houses remained fairly “leaky” until about the 1970’s. 

The Consequences of Trapped Moisture

Since the 1970’s, we’ve exerted much more technological and mechanical control over temperature and moisture in our homes. But temperature and moisture control in home construction remain serious issues that pros spend their whole careers focusing on. Water will always find its way into a home and need a way out. Quality construction using the right materials in the right places can help mitigate these issues.  

And sometimes, today, we wrap our homes up too tight or make choices that limit air flow, creating areas that trap moisture. When that happens building materials may fail (painted brick crumbing from moisture damage or rotting wood).

Moisture collecting closer to the inside of the house, inside the insulation or against studs, may eventually create an interior air quality issue. You could have mold and mildew building up on your insulation or your studs.  

That’s BAD!

Solving the Problem, From the Ground Up

So how to you ensure the right balance of air sealing and air flow? It all comes back around to the question of thermodynamics, the way temperature and moisture move through a mid-century house.

Anywhere warm moist air hits a cold surface, you’ll get condensation. And that can cause mildew, mold, and even permanent structural damage!

Depending on your situation, you can affect your moisture issues with one (or several) of the following general moves:

  • heat or cool the surfaces and/or air inside the house
  • mechanically dehumidify the air inside the house
  • circulate air inside the house

We can also address the question of how much air is being exchanged between inside and outside the house which goes to all of the above

We mostly can’t control what’s happening with the air outside the house although there are a few things we can do there as well

When we add insulation to a mid-century house we need to be careful that we aren’t forgetting to consider moisture. And when we change the “envelop” in ways like replacing wood siding with vinyl, or painting brick, we have to make sure that we aren’t trapping moisture into a system that use to be able to “breathe.”

Insulation and Air Circulation in a basement

I’ll pick on my own basement to talk about this. When I moved into my house I had to demo the existing “finished” basement from the 1960’s because the lack of insulation and air circulation had active mold growing against the foundation behind the walls.

I tore out (but saved) the pickwick pine panelling and took the opportunity to change up the layout, install an egress window well for a basement bedroom and a 3/4 bathroom.

But most importantly, I raised the floor surface up off the slab to that any moisture that ever got into the basement could roll away to the floor drain and I sealed and then properly insulated the walls with an air gap so that no moisture could get trapped behind them and create mold in the future.

This post has some in progress details showing the difference in temperature between the outer walls an inner surfaces on a cold day in 2017.

In Today’s Episode You’ll Hear:

  • Why you should be on the lookout for evidence of moisture issues.  
  • How to tell if you have a “hot” or “cold” roof. 
  • Who to call for testing and answers related to temperature and moisture control. 

Listen Now On 

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Resources 

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Read the Full Episode Transcript

Now let’s talk about temperature and moisture control in mid-century houses. This is one of those topics that seems less exciting and relevant until suddenly it is. And while our mid-century houses have the potential to do very well on being properly snug without being too sealed up. By the way, remind me to get into sick building syndrome and the 1970s some other time.

They also do, sometimes need a tune up, and sometimes seemingly esthetic changes to your houses, siding, soffits or roof can create problems today which didn’t exist during all the decades your home was standing. Yes, I am going to talk about the moisture consequences, and I know that sounds icky of painted brick and vinyl siding.

Hey there. Welcome back to mid mod remodel. This is a show about updating MCM homes, helping you match a mid-century home to your modern life. I’m your host. Della Hansmann, architect and mid-century ranch enthusiast. You’re listening to Episode 2204

I have talked about adding insulation to mid-century houses in the past, and about roofing choices for mid-century houses, but there is a topic that falls in between and is really important to get to, which is temperature and moisture control in mid-century houses. It’s a very specific challenge, and it has to do with the fact that our assumptions and our ability to control human comfort and all of the tools that we employ to achieve it have been shifting a lot in the last 75 years.

Of course, what I actually mean is that that was a snippet of time out of a long period of flux before the mid-century houses start to fill in. But there was a dramatic, I’ll say, increase in the change and the technology implementation across residential architecture, particularly since our era. Just earlier this summer, I was talking again with my friend Adrian Kinney of mid mod Colorado about the way homes in Denver were built, and that in the mid-century, they were still being set up with no air conditioning whatsoever, just a swamp cooler on the roof and a thoughtfully arranged organization of windows to take advantage of prevailing winds for air flow.

Now that has really shifted, and people are retrofitting air conditioning systems into their homes. Now this is not just a factor of us getting more squeamish and wanting to be more protected from the environment around us. It’s also absolutely a factor of weather becoming more intense, and therefore for even issues of safety, but certainly issues of human comfort. We need to address that with changes to our building systems and our homes.

But the thing is, once you go from not having an air conditioning unit to having one, it’s pretty easy to just hit a button on the thermostat and turn it on for many more situations than you would have if you didn’t have it at all. And what we’re going to get into today is the difference between having an air conditioned unit and not or having some amount of insulation or house wrap or not aren’t just a one factor question.

They are holistic systems based things. So this is going to become a little bit of a catch all episode containing a number of lessons in building technology and maybe even the broader concept of thermodynamics that have me reaching back to my graduate school architecture education but also sharing some of the most common sense things about how we build our homes, framing things in hopefully a way that makes logical sense.

Because this topic is important to homeowners. While temperature feels like a purely human comfort issue, it’s just what we like it feels. It’s how we feel. Chill, for lack of a better word. I mean the fact that we use metaphors like chill or cool or warm or hot to describe our feelings gets to how important temperature is to the human experience.

But also because temperature and moisture control in mid-century buildings has the potential to be a serious health issue if it’s done wrong, when moisture gets out of control, we have mold, and mold is a real hazard to look out for in mid-century homes. I talked about a bunch of these and mold, specifically in my two part series for spooky season back in 2023 that would be episodes 1407 and 1408 common health hazards, including asbestos, radon, mold and I believe we also talked about lead paint and VOCs in your home.

So all of these things are not things that should keep you up at night, fearing for your safety, but things you should be aware of when you are owner of a mid-century home. And particularly, some of these things can be removed from the house. Some of them can be covered up. But mold is something that should be in the first place, prevented, and we can do that with temperature and moisture control and mid-century design, this is something we want to pay attention to, and if done right, our building systems will prevent it from ever being an issue.

If done wrong, we can thoughtlessly create a situation that was a problem when there was never a problem before. That leads me into the other important reason that I want to tackle this from kind of a philosophical. Full high altitude approach, a commonsense approach, rather than telling you an answer, because there are a range of scenarios that are going to show up around temperature and moisture control in mid-century houses.

It’s not a one size all fits. One size fits all. Rather solution that I can give you for every home built in the mid-century, it’s going to depend on your climate zone. It’s going to depend on how your house was built. The structure of your house we there are mid-century houses built with CMU block walls. There are many mid-century houses built with stick frame construction, two by four walls. There are also houses built where the structure is separate from the walls, a post and beam style home, and they may have different solutions for insulation than your typical balloon frame, stick frame house.

And in each of these cases, the building technology used in the mid-century is a little different than the houses built since then. So people who come in to do repair work on your house may or may not be familiar with the exact situation you’ve got. Also that leads me into this is an issue that you need to kind of have a high level philosophical understanding of. You don’t need to be an expert. And if you need expert advice, it’s out there for you.

But when you go to solve a problem of temperature and moisture control in a mid-century house, the person who’s going to do that work is a specialist subcontractor. They’re not a general contractor. Even if you’re working with a general contractor on a bigger remodel, the question of insulation and air seal, the temperature and moisture control comes down to different subcontractors with different specialist systems, techniques, materials, suppliers and practices.

So someone is going to be putting in bat insulation, someone is going to be a different organization would be hired to put in loose fill insulation. A different organization would come in to do a spray foam solution. This really reminds me of back in my first job in architecture, when I was working a lot with sustainability and different energy effective and sustainably oriented solutions for homes.

People would come to me as the designer, they come to my boss, really at that point, as an architect, and tell him that they’d talked to someone at an energy fair, or they met a friend of a friend, and they were told that geothermal was the only solution, or they had to have passive solar, or they’d heard that solar electric was really effective, but solar heat in in what solar water heating was really bad, or the opposite?

And basically, they’d just gotten a pitch from one particular technology supplier who, you know, perhaps very honestly believed that their solution was a great one but had a tendency to go apply it to every single scenario. Insulation is another one of those subcontracting categories that falls under the heading of each person, each sort of company or team or crew that does this work has a different product, a different type of insulation service they provide, they specialize in, and they have the materials and skills for they have training in that particular type, and they will tend to believe that that particular solution is the best solution in most cases.

Now, a good quality contractor will take their specialist solution up to some houses, look at them and say, Oh, no, what I do is not the right service for this building. But there are gray areas and there are times when more than one type of solution could be applied. So a crew of folk who are used to doing one particular type are always going to recommend the type that they provide. So this brings us back to a very general mid-century homeowner problem of most contractors are going to recommend to you the solution that they have provided to their last five to 10 happy homeowners.

That’s true if the insulation solution has worked for the last five homes. That’s true if the kitchen cabinet design has worked for the last five HDTV loving gray Shaker Cabinet lovers who may or may not been in mid-century homes. So you are going to be the arbiter of what’s the right choice for your house. And again, like if you’re feeling completely swamped by this, get an independent home inspector to come out and look at your house and give you some advice.

Talk to a range of different contractors who have different systems and ask them to explain to you why theirs is better or worse for you specifically, then another type of insulation, you’re going to have to do a little bit of work here, because every individual person you talk to who wants to sell you their service is going to be inclined to believe and certainly to tell you that their service is the right solution for your house, but they may or not may not be correct, so I recommend you seek out an outside opinion.

A building inspector is a great person for this. An architect is also someone who’ll have some insight. I’ll say, while I do advise my clients on all of this, I wouldn’t recommend that if you have specifically a temperature and moisture control in a mid-century building problem that you come to me specifically because I’m not a building science engineer, I’m an architect, and I have focused my attention on the design of spaces that work well for families and individuals who live in mid-century homes.

But even though focusing on climate control isn’t the deepest part of what I do every. Day, I have a little more perspective on this than the average bear, so I’m going to talk to you about it at length on the podcast today. So I am going to end this episode with some specific suggestions and answers that I’ve shared with my clients and students about their specific problems in their houses. But I again, I’m going to stick to the general I’m going to stick to the higher level concepts, so that you can put these overarching themes onto the individual pieces of advice and sales pitches that you’re getting when you deal with this issue in your house.

Ultimately, it’s going to come down to what we can and can’t control. If we’re going to tackle an issue of temperature and moisture control in a mid-century building, it’s going to come down to a couple of different factors we can heat or cool the air, and to a certain extent, the surfaces inside a house, we mostly can’t control what’s happening in the air outside the house, although there are a few things we can do there to improve air circulation or to use shading devices or even just well-placed trees to keep a cooler pocket of air around our home. Inside the house, again, we can mechanically dehumidify the air, and we can also circulate the air inside the house.

And finally, we can address the question of how much air is being exchanged between inside and outside, which goes to all of the above. So like I said at the top of the top of the episode, part of the reason this is important. Part of the reason the question of temperature and moisture control in mid-century houses is an issue is because the mid-century was a microcosm and a kind of hinge point of changing building technology over the years. So now I’m going to treat myself to a little bit of a building technology timeline.

Once people lived on the Savannah, when we were hot, we took off layers. When we were cold, we put on layers, or we built a fire, we cuddled and huddled for warmth. But humans are problem solvers. We started coming up with more interesting solutions to the problem of feeling too warm or too cold almost immediately and different cultures and places in the world, we’ve solved those problems at varying rates.

A lot of attention in America gets paid to the building systems of northern Europe, but actually they were pretty slow to get beyond the level of a simple roof to keep the rain off and walls to enclose us and keep us physically safe. In England, up to even just a few 100 years ago, the wealthiest of people were living in relatively uninsulated buildings where they tried to warm up certain rooms with cloth tapestries on the wall, a giant open hearth that did not do a very good job of heating up spaces.

The best place to be sitting in a situation like that was on a stone bench, kind of inside the fireplace, as close to the heat source as possible, and then to augment that, people use things like canopy beds or bed boxes, wooden or cloth structures where people again bundled together to create a pocket of warm air at night and keep drafts out. They didn’t really worry about moisture control because they weren’t able to. There weren’t really any air barriers on those buildings. Air was always moving freely and in out right through the walls, taking moisture with it.

In other cultures, in Japan, for example, they also have a cold climate winter, just like in Europe. And people there chose to insulate themselves, specifically in padded, layered clothing, and then to create little pockets of insulation inside of largely breezy air flowing freely homes. So you could sit under a blanket, or you could put a light heat source under a low table and then cover that whole table with a blanket and let a group of people pull up and tuck their legs underneath it. Rather than trying to heat a whole room, you would heat the space where people physically were.

Not too far away with a similar winter climate, Korea took the opposite approach. So a Korean traditional home used a principle of heat rising to warm up a house. Their ondol style house, that’s O n, d, O L, if you want to Google it or I’ll put a link in the show notes. They built their houses up over a crawl space, set on stone pillars, and then they would build a fire in a little hearth just outside the perimeter of the house and direct the heat and smoke through the crawl space in a circuitous pattern, which would then travel underneath the whole building and create a radiant floor effect.

This is a 2000 year old technology, so if you compare that to Europe, they were extremely ahead of the game in human comfort inside of houses. And then there were other climates where the interest was more in cooling rather than heating. So if you think about the technology of buildings in the Mediterranean, it has a lot to do with shade and air circulation and creating air circulation within a building the sort of courtyard structure that you find common in Northern Africa and southern Europe along the Mediterranean coast, which we see, again repeated in California mid-century buildings, because from Spain, it went across to South and Central America and even to North America and the Mexico region, and then it came up along the coast, and we see some of the sort of Moorish design. Into Spanish design, into California culture design, influencing the classic California ranch courtyards, shade devices, air circulation.

But all of these buildings were not properly achieving any kind of effective air seal, because it wasn’t possible to bring this a little closer to our own era of interest, I’ll pick on Frank Lloyd Wright. Good old Frankie gets a lot of praise and borderline adulation for his design skills, pushing the envelope of esthetic designs and structure and building system technologies, for making a lot out of a little, and for leading the charge on the translation from regular, symmetrical, sort of colonial style buildings up to an asymmetrical, organic, flowing building that responds to its topographical environment.

He was interested in shading devices. He was interested in using local building materials, but he was not particularly interested in human comfort. And on the flip side, Frank Lloyd Wright gets a lot of criticism for designing roofs that leak and building systems that were deeply uncomfortable. Famously, in his own home, he put together an early zero corner window, which today we would do with a lot of technology.

But back in his day, he created a visually stunning, invisible corner with a window that wraps a 90 degree corner angle. That’s simply two pieces of glass mounted very close to each other with a little bit of sap in the gap to create an air blockage. This is a design, or, I guess, a philosophy, he uses in his Usonian buildings as well, buildings that fall well within the mid-century, era and umbrella. They are beautiful, low to the ground, asymmetrical, playful. They contain most of the qualifiers that I would pull as cornerstones of mid-century buildings, and they get a lot of criticism for being uncomfortable, leaky and not easy to warm or cool.

I actually like to use the example of Frank Lloyd Wright’s own home as proof that he wasn’t just a jerk who designed thoughtlessly for his clients, but rather he was kind of a dinosaur. When we think about him as a Usonian building designer, it’s also important to remember that he started out decades before that he grew up in and personally lived in an era of less thermal comfort and control in buildings, simply a time when people expected not to be warm inside their house in the winter or particularly cool inside their house in the summer.

So this approach to heating up the air inside of a building, but to assume that you’re not fully containing it, has been the reality of building systems technology since all of time, up until quite recently. Then, in the last few decades, we begin to really assume that we can fully separate indoor and outdoor air and create, in effect, a fully sealed interior environment that we can perfectly control the temperature and moisture conditions for this has not been altogether a good thing.

Now I’m not going to do a whole episode on sick building syndrome, but as you might infer from the name, it’s not a good thing, and it dates from the mid 1970s the short version of it is that we got to a place we were too good at air sealing our buildings, and we stopped depending on any kind of fresh air replacement. So we just thought, we can have curtain walls. We don’t need to have a window for light in the bathroom. If we can have a mechanical vent system and artificial lights, we don’t need to require as much fresh air in our buildings. And we are going to fully wrap and seal our buildings up and then control all the interior conditions with air conditioning.

Now not only is that a kind of an energy intensive solution. But we found that when we sealed people into these buildings, along with filling those buildings up with products and technology based heavily on manufacturing that used formaldehyde, treated wood and still off gassing plastic products, we were basically sealing people into bubbles that were little poison gas chambers, and a lot of people got sick. Hence, sick building syndrome.

The reaction to that, from an engineering or a technological point of view, is probably the passive house movement, which is most prominent in Europe, but you’ll hear about it if you are interested in building technology in the US. Again, this isn’t super relevant to the topic of temperature and moisture control in mid-century buildings. Nor is it the topic of today’s podcast. But the short, short version of passive house is that the goal is to so thoroughly insulate and air seal a passive house building, the metaphor is often that you can heat it with a candle or even just with the energy of the people living inside of it, but they also have to pay very serious attention to air to air heat exchangers, which allow for a transfer of fresh air in from outside.

And then they use technology to make sure that as much of that air as it’s being brought in from outside freshly to give us a break from the interior, toxins, dust particles, off, guessing whatever’s inside the building. And we’re also stripping out and saving as much of the interior heated air and the moisture quality on the inside or the outside before we exchange it. That air to air heat exchanger technology is another thing I’m going to make you go look up separately.

It’s never particularly interested me, but if you’re curious, it is. It’s of benefit, and it’s something you might want to look into, particularly if your interest is to dramatically improve the insulation and air seal on your mid-century home, which you might do by taking on something like a full residing attic insulation foundation insulation project. And it could have dramatic results in terms of your energy use and your human comfort, but make sure that you work with people who are going to help you do that, that are interested in the whole building systems technology, rather than just sealing you in.

So that we’re thinking about not just the temperature, but also the moisture control effects. So it kind of all comes back around to the question of thermodynamics, the way temperature and moisture move through a mid-century house that feels very obscure and abstract, but really I just want to talk to you about the ideas of wrapping up your house warm and sealing the rain, the condensation, the humidity in or out of it in a way that’s going to help you make good choices, because this gets to adding insulation to your house during a remodel.

It gets to whether you should or should not replace windows. It gets to siding that works well for mid-century houses and which doesn’t, and what types of soffit material are appropriate if you are getting into a whole package of something’s failing on the roof. So we’re going to get a new roofing. We’re getting a new gutters. We’re gonna get new up. Now we’ve changed a whole bunch of things about the house. Have you changed systems about your house that have always worked and now something suddenly does not work.

So this came up most recently for me when I got a call about a house that a student has which has condensation building up as a result of a poorly insulated roof. This sounds like the sort of intense problem. There’s condensation in my house. It’s probably going to form mold. I will find an expert. We will, we will get right onto this. But this is the type of homeowner problem that you are likely to encounter. Which is if you first run into one very skilled tradesperson whose job is to solve that problem. They pitch you on a solution, and you hire them. They competently take care of it. It can feel like a really easy solution.

But if it’s slightly more complicated, if you end up talking to a number of different people, this is the kind of area where you might get a lot of different answers, particularly in this client’s case, they felt like their problem would be solved by better roof insulation. And they had rather than the sort of classic, modest mid-century house with a gable roof and an attic inside, they had a sloped roof with no with an exposed interior structure and no sort of cavity to fill with insulation.

So they started talking to different suppliers of roofing insulation and getting questions about, do you want a hot roof or a cool roof? Which is going to be the best technological material for you? Each person they spoke to had, I don’t want to say, an ax to grind, had a product to sell and a perspective, and they started to just feel like there was no way for them to get the right answer.

So I’m going to talk a little bit about the bigger picture of what we’re trying to achieve when we seal and insulate our houses. The temperature and moisture control of mid-century houses is variable depending on some of their qualities but also has a lot of things in common.

So this also, by the way, came up for me this summer. I was goofing around on my staycation week down from mid mob Midwest, and I was rearranging the furniture my bedroom. I shared a few pictures of putting a dresser in two different spots on my Instagram story, and then I also decided to share a picture of the inside of my bedroom closet, which I never got around to painting when I moved into the house, and which has some visible moisture damage on the wall.

It’s due to the fact that there is a temperature and air circulation problem in that area, common to mid-century closets, because none of this house is particularly well insulated. I’ve talked about what’s common for mid-century insulation in houses before, and the answer is, in the early mid-century, they were probably using some sort of bat insulation product, but it is not really comparable to what we use today, and it’s probably sliding down the walls, failing, not, not performing up to what it was originally meant to and certainly not performing up to modern standards.

Anyway, it’s possible to lose a lot of temperature to have a cold surface inside the walls of a mid-century house. One of the ways to prevent that is simply to circulate warm air inside the house. But if there is an area where the air is. Still and relatively warm, moist air touches a cool surface. Anytime warm, moist air touches a cool surface, it’s going to drop some of its moisture onto that surface, and over time, that can create a condensation problem. And in a closed off closet without air circulation, that can create a moisture buildup problem.

So the easiest solution to that short of, you know, tearing off the original redwood, cedar siding I love on this house and re insulating and re siding. It is just to leave the closet door open more of the time. It’s really as simple as that. Then, yes, we’re still, could I insulate this house so that it performed better in the winter? Of course, I could, but I’m not in a place where I’m moving to that direction, yet could I control for the moisture, the humidity in the house at all times?

Well, in the winter, when this is the biggest problem, it’s actually quite dry in here, relatively I personally am not the kind of homeowner who’s running a humidifier inside the house, but you might be, and in that case, the answer is not turn off your humidifier. It’s just make sure that there aren’t any closed off areas air circulating throughout the whole house. You might cut a vent in the wall next to a closed closet door, or you might just leave your closet door ajar.

Not every problem needs an immediate, right now, expensive solution. Sometimes we can address the root causes of the problem. And sometimes we can just sort of stop the problem from recurring right now.

So I think I’m just going to jump in by talking about that basic thermodynamic principle, which we’ve all observed, what happens when more moist air hits a cool surface. So this is how you can get moisture building up in a closet. But this is also, if you’ve ever noticed, if you pull the curtains on windows in the winter, you can find that there is moisture on the windows overnight. If you, if you hark back to the sort of classic image of the deep past, frosty windows as a charming feature. Windows get frost on them because the warm, moist air on the inside hits the cold glass surface, and then it gets so cold that it actually freezes frosts. But you’ll see this in a mid-century house.

I have replacement windows in my house, not my choice, the previous owner’s choice, and they are reasonably well insulated. But still in polar vortex weather, when it’s particularly cold outside, part of the way I make it warm in my house is by not by having re replaced the windows with the most top of the line insulated windows, but simply by pulling down insulated curtains across the windows that largely fill the area from trim to trim, top to bottom, side to side. And get not a total air seal, but a decent air seal, this really helps warm up the house. It really helps me not lose warm air directly through the window glass.

But when I open the curtains, when I open the blinds in the morning, there is often a little bit of condensation there. Because of that, some warm air blew in there, got onto the surface and condensed. The solution to that, again, there’s a phrase in passive solar houses, passive solar, active owner. And I think we get into the habit of assuming that our houses need no daily care or maintenance, no seasonal cycles. We sort of slip into this desire of a zero maintenance house that is always a little bit of a lie, and certainly is, I think, a bit of a problematic attitude for owners of mid-century houses.

In my opinion, the solution to this problem is simply to raise the curtains in the morning and wander around with a microfiber cloth and just get that little bit of moisture mopped up. Problem solved. If I do leave it alone, there’s a particular curtain on the guest bedroom I tend not to bother to walk all the way around to move, and it tends to get a little bit more murky back there. I have to clean it with a bit of bleach every now and then. Confessions of a poor housekeeper.

But that issue a little moisture condensing on your windows when it is cold outside is easy to solve because it’s visible. It’s a much bigger problem if that same condensation process is happening, if moist, warm air is touching a cold surface, somewhere hidden inside of the systems of your house, inside of the walls at the outer boundary of the building. This is one of the many reasons why I am so persistent in recommending against painting brick and also against vinyl siding for a mid-century house. Because in both of those cases, what the homeowner thinks they’re doing in the moment is giving their house a quick and inexpensive cosmetic upgrade. A fresh coat of paint over dirty old brick makes it look new, right?

Well, we can have an esthetic discussion on another day about why painted brick is inappropriate for mid-century, in an era way, in an esthetic way. But I really want to talk about this from a technical point of view, today, creating a moisture barrier, an impenetrable layer at the outer edge of the house, is actually creating a place for water to be trapped. Now this might happen in the form of rainwater, which you might think at first, if it rains against a painted brick wall, the paint will keep the water out so it won’t be inside the wall, not a problem.

In that case, I’ll tell you what my grad school building systems instructor told me, which is that water will always find its way inside the wall. It just gets there, and then we have to talk about the ways to let the water back out. Letting water out of the wall is one of the most important design considerations of any wall. The system doesn’t need to be complicated, but it does need to exist. This is why we have flashing. This is why we have weep holes. This is why engineers spend their entire careers designing building systems that let water get back out of walls.

But in a homeowner situation, if you paint a brick wall, and then in the next few years of the freeze thaw cycle, a few cracks in that paint develop at the top of the wall, a driving rainwater hits those cracks, works its way inside. It will now run down the inside of the wall and look for places to get out. This creates water pressure, which tends to make the paint bubble and buckle and come off more, which creates an esthetic problem, again, but it might also mean that some of the water just stays inside that wall.

Honestly, sort of best case scenario is that it drips out, that it makes the paint fail, that it creates a freeze thaw cycle that could crack the brick. It can cause the brick to want to separate from the house that it’s been neatly amounted to this whole time. But the problem we’re talking about today is temperature and moisture control in a mid-century house. So the issue is, water gets in. It’s trapped somewhere inside your wall system.

The same is true of vinyl siding. When a house did not originally have vinyl siding, but it’s been added in the last 510, or even 20 years. This means that a house that once performed perfectly with its existing systems for breathability, had a workable proportion of soffit vents, for example, had a good system of temperature and moisture control. In a mid-century house now begins to fail because the conditions have changed. Now it’s not breathing through the gaps in the paint underneath wooden boards. Moisture is sealed in by that vinyl, and suddenly we’ve got an issue, and that issue is all the more important because it’s not easily visible.

So we were talking about how rain finds its way in and out. But it doesn’t have to be rain. It could simply be warm moist air, and when it’s warmer inside the house, that warm moist air is seeking to slowly work its way out. A lot of it will end up going up because heat rises, but some of it will work its way out through the walls, simply because electrons move from excited to less excited states and warm is always moving outwards towards cold, everything else being equal. So now you’ve got warm moist air from inside the house in the winter slowly working its way out. And there are always places for warm moist air to work its way out through your walls, around electrical outlets or vent openings or particular areas of concern.

Or if the rest of the house is intact, but your windows are replaced, there are often little gaps around the trim of your replacement windows that aren’t perfectly sealed against the wall, and that’s a pathway for air movement anyway. Now we’ve got moisture getting into your walls, into the cavity of the wall, into the material of the wall, not just condensing on the inside surface. So wherever that transition point is in the temperature, that’s where the water is going to accumulate. It might be against the two by four studs of the house. It might be amongst the insulation. If it’s finished insulation, it might not have any kind of air seal. It might also not have any kind of mold or mildew resistance inside of it, or it could be up against the border of that new surface, the paint on the brick or the inner edge of the vinyl siding.

And this is how a mid-century house that has never before had any moisture performance issues can suddenly develop that a newly vinyl sided house actually a vinyl sided house of any age, it makes it almost impossible to recognize this issue without taking off some of the siding and looking at the inside of it, which is it’s not designed to do and in a newly painted brick wall, you’re not going to have immediate health related or mold related issues inside the house, but that moisture accumulation is eventually going to create an esthetic and a structural issue.

You might start to see the bubble and peeling of the paint. You might start to see spalling, which is when the outer surface of the brick starts to Blake, break or crumble away. So the fracture is happening not between brick and paint, but inside the brick, because there’s a moisture issue. This is a real pain to deal with, or eventually, the entire sort of brick chunk might just sort of start to separate from the house itself.

Extra moisture trapped inside of a brick wall is going to freeze eventually, almost anywhere in America, very often, if you’re here in the Midwest, and eventually. That freeze thaw cycle of swelling and contraction is going to get the paint cracking and flaking right back off that wall. So painted brick looks neat and tidy for the first time, if you like, that sort of thing, but painting over cracking and flaking brick does not look neat and tidy. It looks crappy.

So as well as being an esthetic issue for a mid-century house, it is bad all the way. Now, if the moisture drop were happening slightly closer to the inside of the house, inside the insulation or against studs, for example, now you’re getting into a place where you may eventually have an interior air quality issue, mold and mildew building up on your insulation or your studs. Now it is very unlikely to actually do structural damage. But mold is a serious issue that needs to be regarded as a health threat, and mold you can’t see is in many ways more dangerous, because it can build up to any amount without you being aware of it, until you actually start to experience noticeable health issues.

And health issues might be something that you don’t notice and attach to something’s wrong in my house right away, because they creep up on you. This is a place to take concerns about mold extremely seriously, and if you want to go further, I would recommend that you follow up on the CDC or the EPA websites, which still seem to have a lot of good information.

So we’ve kind of talked around the issue of thermal and moisture control on the main floor, and even though mid-century houses don’t have the insulation R value ratings that modern homes do. It’s often not the best area to focus on when you’re adding insulation. It’s not super helpful to try to make big changes to your thermal control in this area, I don’t recommend you tear off all your original siding to get at the interior of your exterior wall cavities.

I don’t recommend either that you go around demolishing all your interior drywall or plaster to add insulation to the house. Either there is a quick fix solution that some companies provide, which involves drilling little holes into your interior walls between each stud, so that you can jam a nozzle in there and blow or send in foam that expands into the wall cavity between each two by four stud in the wall. This sounds good in theory, but it doesn’t work very well for mid-century homes, because it’s not that there is an empty cavity lacking insulation in there.

Usually there’s some sort of early proto bat insulation that’s either degraded or never was really going to perform properly, but it’s something that’s interrupting so you don’t have an empty box to fill up with a good, clean, modern foam insulation. What you have is a sort of a complicated, labyrinthine space in there with old BX cable wiring, ductwork, objects, and maybe sagging or slipping former bat insulation. So you’re not going to get a really good, effective, thorough floor to ceiling insulation value out of that. And it ends up feeling, to me like a bit of a wasted opportunity. There are better places where you can spend the same amount of money and effort to get a better insulation improvement and also a better moisture seal improvement.

Let’s talk about what’s happening below the main floor of the house for a moment. We’ll focus on the basement if you’ve got one. This has come up most recently for several of my clients. Although my ready to remodel students have been asking questions about insulating their roofs and attics, my clients have been having questions or concerns about moisture and temperature in basements.

As it happens, although we do projects all over the continental US these days, I’ve got two on two design master plans that we just wrapped up in the Greater Milwaukee area. And it may or may not have been in your news, but it was big news right here that Milwaukee just got a complete drenching. Big rain system was moving across the Midwest and kind of got stuck on the edge of Lake Michigan, and rained very heavily for a 24 hour period, which caused all the rivers to run up to the top of their banks, parking garages to be filled, inches or even feet with rushing water and basements to fill.

So the first question I asked each of these clients when we had our scheduled workshop call was, how did you do with the storms? Did you get water in your basement? This is a question Midwesterners ask each other after a storm. Did you get water in your basement? And if you live in another part of the country and your homes are typically built on crawl spaces or slabs, you might think it’s weird to need to ask that question, why have a basement if it’s likely to get water in it. But we build basements in the Midwest so that we can have a foundation that goes below deeper than the frost line, the level at to which the ground will freeze in a cold winter, so that the freeze thaw cycle doesn’t literally push our buildings back up out of the ground. Because yes, that is a thing that can happen.

So we need deep footings in the Midwest. Well, in Wisconsin, in my climate region, particularly, it’s about a four foot frost footing. So you’re digging down four feet below the soil level, you might as well dig down three more feet or four and you’ve got a seven or eight foot basement, and boom, that’s double your square footage. It’s great. But sometimes the area that is both below the frost line and above the water table might be an overlapping Venn diagram in a case like that. There’s still a lot we can do with French drains around the house, with grading and landscaping so that water that falls in the vicinity is directed away from the house.

We can also put in mechanical drainage sump pumps, which are basically tiny little wells in the basement that fill up with water, and then, as they fill, a mechanical pump takes that water away and puts it into the municipal drain system. In normal circumstances, it’s a fairly easy problem to solve, to keep water out of your basement, but it is important to address this. It is a serious problem that can easily be solved. Storms can be a problem for letting water into Midwestern basements, if, for example, your system works perfectly, as long as the pump is always pumping, but the power goes out and suddenly those little walls are flooding because the sump doesn’t have power to run.

So in one of the conversations I had with a client about did you get water in your basement, they volunteered that their plan before the next storm is to get a generator so that should the power go out, their pumps will not fail. I think it’s pretty obvious that you don’t want to have standing water in a basement, finished or unfinished. That seems like common sense.

Do we all agree on that good solving that problem is something you can easily get a specialist company to come they might cut out the outer perimeter of your entire basement slab to put in drainage and install a couple of sump pumps. These are extreme measures, but they’re easy to do, particularly in an as yet unfinished basement, and it may very well be that actually at this point, if that hasn’t happened already in your house, it probably doesn’t need to happen. Most basements in the Midwest of mid-century, homes that need a sump pump have a sump pump might be needed to be improved on or checked, but you’re probably good there.

But active flood waters in a basement are only part of the problem. You might also just have moisture accumulating in your basement. Basements can be humid. Moisture from the surrounding soil can seep in as a vapor rather than as water droplets, and also sometimes in a big storm, little bits of water can infill, infiltrate into the basement in some place and accumulate on the floor in a well-designed basement, the slab should always be oriented with a tiny bit of slope towards either one or several floor drains. So basements should always drain over time.

If a little bit of water gets into the house, it’s not necessarily a problem, as long as it can drain away. It can drain away again. This is a reason, though, where, when I am finishing a basement, I never want to put a finished floor material directly onto the concrete slab or directly up against concrete walls.

My favorite detail for insulating a basement, and I will put a sketch of this, a drawing of this into the show notes page is to keep everything away from the floor and away from the walls. Start with a sub floor that has a built in plastic spacer beneath it that creates about a quarter inch of air gap between the concrete floor and the sub floor, which is OSB, or oriented strand board. Then on top of that sub floor, you build your walls, and then you put in your finished flooring, and that might be wood or cork, an engineered product, linoleum, tile, what have you, but none of it is directly in contact with the basement floor. And that’s because if you ever have that temperature moisture differential in the basement, which causes water vapor to be dropped from a warmer interior air onto the cold concrete floor, there’s a way for that floor to then let the water move away, let the moisture on it roll downhill to the floor drain and leave the basement.

This occurrence, this what we call when moisture accumulates on a cold basement surface, we call that sweating. We say that the concrete is sweating. That does not actually mean that the moisture is coming from the concrete. It’s actually just being dropped from the air onto it, but it looks like it can sometimes look like little beads of water or dampness on the floor. That’s not because moisture is coming in. It’s just that the concrete surface is cold. The air is warm. The warm, moist air drops its water on the surface. This is why I really like to air gap between the finished floor and the sub floor together, and then the separate space between the concrete floor of the basement the slab.

So circling back up to the different sort of philosophical techniques we have for temperature and moisture control in mid-century buildings, this is getting to a way to control moisture. That is, we’re going to control what’s happening outside the house by directing water away from it with landscaping. We’re also going to try to control the actual moisture content of the air inside the house to prevent moisture from accumulating, and this might be with sump pumps. It also might be with air conditioning, and certainly it’s going to be in a basement with running a dehumidifier as needed. Mechanical dehumidification might be your whole house air conditioning system.

Or it might just be you get a dehumidifier unit or several and set them up as needed to run all the time on a sensor with a little drain hose running not into a bucket that can overflow, but right to your floor drain and away.

And the third technique we’re using to control the temperature and moisture is air circulation. That’s because we’ve got the spacing so that your finished floor and your sub floor are up away from the potentially sweating concrete floor.

So head over to the show notes page and check out that sketch detail, because there’s also an air gap component between the insulated and furred out basement finished interior wall and the either concrete block or part concrete foundation wall.

In every case, we’re just looking for opportunities to not let moisture accumulate on a finished surface. And if moisture is going to accumulate on the concrete foundation or basement slab, it’s going to have a way to then be blown away or roll away so it’s not stuck there, creating an opportunity for mold.

The other component of a good basement, insulation detail that’s going to do well for temperature and moisture control is going to be at the rim joist. This is the space just it’s sort of this. This the space of the floor between your basement ceiling and your upper floor, there are a number of joists, and at the outer edge of those joists is a piece of wood that’s the same height as those joists. It’s called the rim joist, and it runs all the way around your house.

In some cases, at the rim joist, moment you have the thinnest separation and the least insulated separation between interior air and exterior air. It might just be your outside siding, whatever kind of building wrap or paper or fiberboard that is underneath your siding, and then that rim joist, and that’s it. This was the case on my house. And in fact, again, show notes page. I think I’m going to use this as the header image, because I love it.

I once had to install a vent fan from my basement bathroom, and so I took a four inch hole, saw and drilled a four inch diameter hole through the rim joist of my house to make a spot for the vent fan to exit. And it’s really visually interesting to peek into that hole and see the thinness of the separation between in and out. And also, I pulled out the layers and stacked them up, and they look like a cute little like a macaron cookie or something.

There’s a common homeowner solution that’s a little under informed and doesn’t perform well for this, where you just cut out rectangles of bat insulation and lightly press them into the gap between joists. This does create a little bit of a thermal barrier. It warms up the outer edge of the house and slows down heat loss from the basement. But if you’ve been paying attention, you’ll notice that this is actually an opportunity for hidden moisture accumulation to cause problems, because there’s no air barrier at all in that which means moist, warm air from the interior can move through that sort of process as it wants to.

And it could drop off the moisture wherever that drop the moisture temperature differential hits, if it’s cold enough, it might be inside the bad insulation generating moisture in there, or it might be on or inside of the wood of the rim joist, or it might be all the way on the outer edge of the house, up against the vinyl siding that’s been added in the last couple of years, or the last couple of decades, causing moisture to be building up against the outer edge of the wood rim joist, which is particularly bad. That is moisture trapped against a rot-able surface.

So what can we do to prevent this? We can put in an air barrier, and we want to put the air barrier into the system close, as close as possible, to the warm side where we can stop moisture from ever needing to drop. The detail I chose for my house is to put up against the rim joist two layers of two inch thick rigid foam insulation, the pink foam, and then put a nice moisture seal with a bead of caulk around the inner edge.

So I have prevented any air from traveling through or most air from traveling through the rigid insulation or the caulk. It can sort of work its way into the wooden joists, but that’s a slower process. So basically, now the temperature change is happening in an air sealed area away from the warm, moist air of the house. How many times can I say warm moist air in one episode? My goodness, many times. But that way, moisture will always be dropped on the inner side of that insulation where I can see it, or, better yet, it won’t be dropped at all, because moist air never gets cold enough to need to drop its inherent moisture. Perfect. Again. I’m going to see if I can come up with a sketch, or certainly a photograph, of what a good version of this detail looks like. If you want to pop over to the show notes page, you can see it there.

So let’s come back to the inciting incident for this episode, getting two questions, one after another, two months in a row on the Office Hours calls about roof and attic insulation and ventilation. The first one was really about a client struggling with a slightly unusual, a less the less common version of a mid-century roof. Mid-century houses come in two flavors of roof, the kind with a triangular attic that you can add insulation inside of, and the kind where your roof structure is on the inside of the house. And so there’s no attic container to insulate.

So in this case, this ready to remodel student had the second kind of roof with interior exposed structure. And this does make for a slightly different situation. They’ve been talking they have a moisture issue in their house. Moisture is accumulating because they don’t have proper insulation in their roof, a cold surface. And they’ve been talking to a bunch of different contractors and getting a bunch of questions about which do they even want a cold roof or a warm roof? And they’re wondering, well, what the heck does that even mean? And also, they’re just being told a bunch of different a bunch of different companies are all saying, My solution is the best pick me, and that can be a really overwhelming situation to be in as a homeowner. And we talked about that at the top of the episode, too.

So I’m going to kind of repeat the answer that I shared with this particular ready to remodel student who came in and asked, you know, what can we do? We’ve got a moisture issue that’s accumulating on our roof. We have an exposed structure with no insulation between the trusses, and as each different company is making a different recommendation, there’s no consensus. So what can we do to increase the energy efficiency of our single level exposed structure home, and hopefully stop this moisture problem from happening too?

So this gets to the question of a cold versus a warm roof. And if you start looking at roofing insulation, you’ll hear these terms. It only really makes sense, cold versus warm, if you think about the temperature differential in a house in cold weather. When it’s colder outside the house than inside the house. In your classic post and beam mid-century house with exposed joists on the inside of the room that will be a warm roof, any insulation that’s added to that house will be outside of the structure and outside of the thermal envelope, the bubble of the house. Versus the classic, more modest mid-century structure, the Midwestern ranch house with a little triangular attic that’s a cold roof, because the whole attic space is meant to be colder than what’s happening inside the house, the temperature barrier, the insulation happens on top of the ceiling of the house, and the roof itself and the attic itself are cold spaces, not warm spaces.

So it might be as simple as just, are you dealing with an exposed structure, a post and beam style mid-century house or an attic style, a classic Midwestern ranch mid-century house that gives you your answer of cold versus warm roof, it might be slightly more complicated than that. However, if you have a very low sloping a low pitch roof with an attic, you might or might not be able to get enough insulation into the attic cavity.

You may also just have existing systems in place that you want to augment or work with. So you’re going to want to ask basically the more thermodynamics based question that we’ve been talking about this entire episode. Where do you want to create the air barrier, and where do you want to create the temperature barrier so that you never get a situation where warm, moist air is right up against a cold surface.

And this leads right into the question that was asked the following month, not really as a follow up, although it was a perfect segue, which was about soffit ventilation. So the soffits are the flat surfaces that extend out from your ceiling and are the underside of the overhanging edge of your roof, and soffits should have vents in them so that air can come up from the sides of the house, and rather than getting sort of stuck against the underside of your roof, it’ll be vented in and go up through your attic cavity.

Again, if you’ve got a type two, if you’ve got a mid-century house with an attic, not an interior exposed structure, a poster beam house, you want air to be able to circulate through the attic and out through upper exterior vents. Those vents might run along the gable, the top pinnacle of the roof, or they might go out the gable ends, the sort of flat, triangular ends of the roof, if you have those. In either case, you’re trying to use natural stack effect ventilation, the fact that hot air always rises to keep air moving through your attic and prevent moisture problems inside of the attic.

This is helping to maintain a cold roof situation wherein you’ve created your insulation barrier right on top of the ceiling, and then outside temperature air is circulating through your attic and going out the roof. System itself, the only purpose it’s really serving is to create a water barrier. Rain falls from the sky. Snow falls in the sky. Objects fall from the sky.

They hit the roof, they roll down a slope, they leave the roof. In the Midwest, we need a steeper pitch of slope to keep snow from building up on top of the roofs. In drier climates, that’s less necessary, and that’s why you see a lot more flat roof designs or low slope roof designs in areas where it does not snow. It also, if you were ever wondering what that sort of very picturesque Alpine almost a frame style of house, the more the likelihood of a snow load is in the winter of a climate, the more appropriate it.

A very, very steep roof to make sure that snow sheds right off the roof, although in certain cases, and I think I’ve talked about this on the podcast before, snow accumulating on the roof itself can create an insulation, a temporary insulation surface, and can increase the insulation of your house against exterior extreme cold. But that is less useful.

Now, it’s not always colder outside the house than in, and when it’s hot outside, the sun can beat on a dark roof surface and create a very hot condition inside the attic, which, again, eventually, even though heat rises, can start to radiate down into your house and heat your house up. And this is why, again, air circulation, when there’s hot there’s kind of a bubble. If you don’t have enough venting, enough air circulation in your attic, you can create a hot bubble right over your ceiling that will radiate into your house and make your whole house hotter.

So how do we prevent that with soffit vents? And the trick about soffit vents is you always want to have the air movement going upwards, even if heat isn’t rising. You want positive pressure so more air should come in low, and then a little bit less should be able to get out above. You want more soffit air, square footage than ridge vent, square footage, so that air is always flowing up and it’s never being pushed out and down. Your soffits to get just a little bit technical, and yes, I will put this in the show notes page.

There’s a formula for how much area of soffit vent you should have compared to the area of the ceiling area in your house. So it’s generally considered to be one square foot of vent for every 150 square feet of attic floor or ceiling in your house, if the attic floor has been thoroughly air sealed and has a vapor barrier between the inside of the house and the attic, that equation is actually more forgiving. It’s one square foot of vent area for every 300 square feet of attic floor.

Or in the reverse, you need half as much soffit venting if you have a good air seal? Do you have a good air seal? Is an important question to this situation. In a modern construction, that means there is actually a vapor barrier. It’s usually like a plasticky paper, something that’s laid on top of the finished ceiling in the house, in a mid-century house, you may actually also still have a good air seal, even though that certainly was not the building standard in the area.

If your house has interior plaster finish and a good solid paint and you’ve never had any major remodeling work done inside the house, you might have a pretty solid air seal, just based on the completeness of mid-century construction standards. If your windows have been replaced, or your doors have been replaced, that’s less likely to be true, and this, again, to get slightly technical on you, you might want to get a blower door test done on your house. This can sometimes be done for free by local by grants served by local municipalities, or you can hire an energy efficiency company to come and do one of these.

It’s a simple operation. It takes just a couple of hours for them to do an energy assay of your house. They might also point an infrared camera at the house and see where you’re losing or gaining heat through your windows, through your walls, et cetera, and give you an estimation of where would be an efficient place to insulate.

But a blower door test is going to tell you whether you’ve got good air seal in your house or not. House or not. Why does this matter? Well, it’s more important to be controlling what’s happening with the heat in your attic. If moisture can be going through again, we need to know where the moisture barrier of the house is. But if you have a good air seal in your ceiling, then what you want to do with a gable roof is just simple fill blown cellulose insulation can do the job for you, and if not, then you’re going to need to think about something that also creates an air barrier.

An even more simple way to think about this, though, is when in doubt, you probably need more soffit vents. If your house has its original soffit vents, and they are a very classic mid-century detail. It’s just those cute little round plug ones that are absolutely adorable. They’re also probably absolutely nonfunctional, because they fill up with detritus from the attic over the years and they were at best, approximately point 05, square feet at maximum of an opening.

So simple math, you would have needed 66 of them working perfectly, even for a well-sealed ceiling surface, to properly vent the attic of a 1000 square foot house. You probably don’t have 66 of them. If you go and talk to a roofing company about soffit replacement, they’re probably going to try to sell you something that they’ll take out your plywood soffits and put in a new vinyl or possibly aluminum interlocking system that has some sort of vent pieces in it.

Functionally, that’s probably fine. It’s not my favorite esthetic, but it can work as long as you have the right proportion of vent able area. But my personal preference is to notch out one long linen. Your vent that runs the entire length of the roof edge, the sort of gutter line of the house, and that you can really control. It can be relatively narrow because it’s continuous, and you can screen over it properly so it doesn’t cover up with detritus and get plugged up. And then you can maintain or replace your original plywood soffits. That should be just fine.

Now, not everybody has a plywood soffit. Some people have exposed rafter tails. There are more complexities than this, but basically, if you have the mid-century type of house that has a cool roof, you could probably do something about improving the ventilation, the air circulation in there. You can probably add more soffit vents. When in doubt, always add more soffit vents. If you have the other type, if you’ve got a post on beam house, and therefore you have a warm roof, the only way to add insulation on the inside is start to destroy that exposed structure.

So probably to improve the insulation quality of an existing warm roof system, you’re going to be need to thicken the roof itself. You’re taking off the outer layer, adding inches, maybe multiple inches, of insulation. And sometimes there are details that are it’s possible to have a thicker amount of insulation over the house itself, and then have it actually thin, almost taper, as the roof edge is exposed beyond the walls of the house.

So you can still have a relatively graceful, narrow facial line. There are a bunch of details we’ve worked with clients over the years to solve this problem in different ways. But if you’ve got a lack of insulation in that type of roof, you’re going to be adding it on top. You’re putting sort of more hats on top of your hat, whereas if you have an attic Gable and a cold roof style, or a cool roof style, you’re going to be adding insulation inside of your attic, rather than it would be almost useless or counterproductive to try to insulate under the shingle or whatever your finished roofing surfaces.

If you’ve got an attic, you’re not trying to make the attic warm. You’re trying to keep the house warm. So I have in no way covered every situation that is possible in a mid-century house, not just in mid-century roofs, but basements, slabs, crawl spaces, insulation, but hopefully, by thinking about this on the broader level as the sort of thermodynamic building science approach to temperature and moisture control in mid-century buildings, you’ve got a little bit more of a First Principles understanding of what you’re trying to achieve.

If you’re stuck on this, you’re probably best off contacting a building scientist, someone who specializes again, I would talk to an independent agency, an independent inspector, rather than necessarily taking your actionable advice from contractors or subcontractors who provide a specific service and therefore will be lightly or greatly biased towards the benefits of that service. But you can also reach out to me. If you’re a client or a student, I’d be glad to help you with this project and finding the balance between, yes, we all want to improve the energy performance of our buildings, but also not creating new problems by solving old ones.

It is all too common to see that moisture problems can begin in a mid-century era house after decades, you know, 50, 60, 70, years of performing just fine, having no moisture issues whatsoever, we can create new moisture issues by messing with the thermal control by the insulation of the house, and not properly considering how moisture is going to behave in that system. Long story short, don’t pay your brick. Long story longer, just think about, where is that boundary between warm and cold surfaces, and I’ve talked predominantly about how warm houses behave in the winter.

This is in some other climates, much bigger issue for how outside, warm humid air can drop its humidity against the cold surface of a very thoroughly air conditioned house. That’s also something that can happen. So this sort of works in both directions. And in certain climates, we are hot in the summer and cold in the winter, but in Midwestern climates, we generally still focus on that winter performance issue and assume that in summer, air movement is going to solve any kind of major moisture accumulation and therefore molding issues in any case, hopefully this has given you a little bit more grounding.

Hopefully you found this fun, and I had a few why and what and where for history digressions to make it not totally technical. And to hit those technical points, I will put some of the diagrams. I’ll put a couple of other people’s sketches pulled from Handy Pinterest searches and the formula for your soffit equation all into the show notes page, so you can go grab them there. But I hope that you’re feeling a little bit more aware of temperature and moisture control issues in mid-century homes and how specifically in your house, you may have noticed things that have happened over seasons repeatedly, and now maybe you have a little bit more of a jumping off point of how to go solve those problems.

The show notes for this episode you can find at mid mod, midwest.com/2204, and that will also have a transcript of the episode if you want to skim back through what I’ve been saying in greater detail, hopefully you’ll find it useful.

Next week, I’ll be back with something really fun, another interview with Jim Drzewiecki of ginkgo leaf studio. He is a regular guest on the mid modern model podcast because people keep asking questions that mean I need to go ask him questions about landscaping for a mid-century house.

And next week, I’m particularly excited to share this episode because we’re going to be talking about sort of first steps or DIY design guidance for people who want to make their own choices, if you’re not necessarily looking to hire either a landscaper or a landscape designer, but you want to make better choices for your mid-century home’s yard.

Next week’s episode is going to be an excellent jumping off point, so I will see you there for that. And in the meantime, I hope that you are staying just as cool or as warm and dry as you would like to in the current season of your mid-century home.

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