Andy Wojtowski

Podcast: Old houses vs new houses, part 1

Today the gang digs into the pros and cons of old houses vs new houses. We all know that we don’t build them like we used to, but is that a bad thing? New houses are more energy-efficient, but they’re also less durable. This the result of less drying potential, different building materials, and different building methods. The gang also discusses moisture management, building science, and vapor drive. Tessa also discusses a new “perfect wall” system.

This excellent video on basement insulation methods is also mentioned in the podcast:

Here’s some information on the Perfect Wall system that Tessa mentions:


The following is a transcription from an audio recording. Although the transcription is largely accurate, in some cases it may be slightly incomplete or contain minor inaccuracies due to inaudible passages or transcription errors.

Tessa Murray: But I don’t think one is necessarily better than the other. They’re just very, very different. And there’s pros and cons to each. And one thing about new houses though, is that, like Reuben said, “Old houses are a lot more durable”. A lot of it has to do with building materials and the way that we build houses nowadays, but new houses are a lot more fragile.

Bill Oelrich: Welcome, everybody. You’re listening to Structure Talk, a Structure Tech presentation. My name is Bill Oelrich alongside my co-host, Tessa Murray and Reuben Saltzman, and on today’s podcast, we are gonna talk a little bit about new houses versus old houses and some of the challenges that we see with both of them. And Tessa is well-qualified to give us the building science background on these things. And I think everybody thinks new is always better than old and then there’s this small group of people who think old is the best thing ever. And I’m raising my hand, but you guys can’t see that, obviously.

Reuben Saltzman: You know, everybody says…

TM: A lot of people.

RS: They don’t build them like they used to. There’s a lot of people. Die-hard fans of old houses and they will not have it any other way.

BO: Well, when the heating bill comes and it’s $800 a month then sometimes you reconsider your choice of old versus new, but…

TM: There is that.

BO: So let’s dig into this. And I feel like there’s three kinds of houses, not just two. I feel like there’s houses that were built before the mid to late ’70s, and then there was this experimental age that included the ’80s and the ’90s when wood became made of chips and fibers and things of that nature. And then we went through some challenges there, and then we have our new concepts and how we use new building products that are still made of chips and pieces of wood, but at least now we know how to build these structures. So anyway, that’s background for my mind, what I see as the world of building. How do you see it, Reuben?

RS: I don’t like to say one is better than the other. I just like to say that they’re different. Old houses, without a doubt, they’re way more durable and they’re way less energy efficient. I mean, that’s really the biggest difference I can think of. What do you think, Tessa?

TM: Yeah, comfort’s a part of that too, probably.

RS: Sure. Sure.

TM: Yeah. But I agree with you, Reuben. I don’t think one is necessarily better than the other. They’re just very, very different. And there’s pros and cons to each. And one thing about new houses though, is that, like Reuben said, old houses are a lot more durable. A lot of that has to do with building materials and the way that we build houses nowadays, but new houses are a lot more fragile than old houses.

RS: Yes. Yes.

TM: And all it takes sometimes is one little leak somewhere and it can just blow up the whole house.

RS: Yeah.

BO: Like an explosion blow up or?


TM: Like mold and deterioration and rot and all sorts of things.

BO: Okay, wow.

TM: Air quality.

BO: So fragile. I never thought that fragile would be a word used in…

TM: To describe a house, yeah. The more energy efficient we build houses and the more building materials change, it’s very important that the way houses are put together is done correctly, and the way that we maintain our houses has to be done properly, too. There’s a lot of different things with just occupant behavior that can destroy a house today.

BO: Do you have a set age where handymen are allowed to work on a house? And then when they get into a certain age category, they are no longer…

TM: It’s not even handymen. I’m just thinking just the occupants themselves. So one of the big differences between old houses and new houses; old houses, there wasn’t much insulation in the walls, if anything, and a lot of the wood that was used to construct these walls was actual wood, pieces of lumber, right?

RS: Yeah. A slice out of a tree.

TM: A slice out of a tree and a lot of those trees were old and so they were… The wood was more durable. Old-growth lumber. So when an old house if there was… Let’s say there was.

RS: Wait dig into that, Tessa. Old growth lumber.

TM: Old-growth lumber.

RS: How is that more durable than today’s lumber? Why is it different?

TM: There’s a lot more heartwood. Right, Reuben? So older trees have more heartwood in them and heartwood is more… It’s naturally decay-resistant, bug-resistant, pest-resistant, all these things. Whereas trees today, a lot of trees we use for construction products and other things, furniture, they’re grown on tree farms, and so they’re grown as quickly as possible and they don’t have as much heartwood. And so they rot and decay much faster.

BO: So let’s, you guys both had a twinkle in your eye when Tessa said heartwood. So where is that in the tree? I imagine it’s in the center, but tell me why it’s so much better?

RS: No, that’s exactly it. It’s in the center. It’s basically the cells of the tree. And I’m not a building science guru like Tessa but I’d say the cells of…

TM: I’m thinking of Bob Seidi, my old professor at the U of M who taught classes on wood. I had to take classes on different, on wood.

RS: Right, so correct me if I’m wrong, Tess, it’s like the cells…

TM: Don’t ask me to remember those things. [chuckle]

RS: Are basically filled? They don’t have openings, they’re not going to take on water which is what makes them decay resistant. They take all the nutrients for a tree up and down. They’re closed off. They can’t take anything else. Now, the stuff on the outside of a tree, the sapwood. That is much more open and that will accept a lot of water and that’s where it rots much more quickly. And if you’re gonna have that exposed to the elements, you have to have all that wood painted. It’s gotta be painted.

TM: Protected.

RS: If you got a board, you gotta paint all six sides of that board, top, bottom left, right and the ends. You gotta seal if off. And if you don’t, water is gonna find its way in there, and it’s gonna rot it out in fairly short order. And when I say short order, I’m talking like 10-20 years.

BO: Okay, so…

TM: Or even less. I got on a tangent, though, I’m sorry, Bill, go ahead.

BO: Well, is there capillary action occurring inside of heartwood? Like would occur… We always talked of capillary action it can be sucked up into any wood so is heartwood immune from capillary action?

TM: No.

BO: Okay.

TM: Water can still wick up.

RS: How far?

TM: All the way.

RS: Okay.

TM: Yeah ’cause water can wick up a tree from the roots to the top, right? But anyways, we got on a tangent, but the difference between old house and new house, so these old houses, the walls were a lot of times they were empty, very little insulation, if any, built with this old durable wood. So let’s say you had a small leak around a window, which Joe Esherick calls windows water injection.


TM: What’s it? Water injection systems, basically. So you put a hole in the wall, you put a window in. If there’s a small leak around that, well, you’ve got a lot of heat that can move through that wall system, because you’ve got air leakage and all these things happening where you’re gonna have airflow in these empty wall cavities that can dry out those wet areas. Whereas a new house today, you take the standard wall and it’s full of insulation, because we’re making our houses a lot more energy-efficient, more comfortable, you’re losing less heat. And houses today are a lot more airtight, too. They actually, they have to be a certain air tightness, at least in Minnesota, to meet the energy code. And so you have a house that has very little or no airflow through a wall cavity that’s filled with insulation. And on top of that, we use vapor barriers. In the Minnesota on cold climate, we’ve got vapor barriers on the warm side of the wall, just basically like plastic.

TM: So the other thing too is we use like OSB and other wood composite products to build our houses today. So you take building material that is much less durable, basically, it just turns to mush when it gets wet. It gets really moldy easy. You take a wall where there’s no airflow and no heat getting to it, and you put a Ziplock bag over it, what’s gonna happen when water leaks in around the window? It’s gonna destroy it.

BO: So, then preventing the leaks is probably a pretty important thing.

TM: Yeah, exactly. That’s why we say new houses are a lot more fragile. They’re a lot more energy efficient. You’re not losing all this heat through the walls and through the building envelope and everything, but you’re also not able to dry things out when they get wet. So a lot less durable.

RS: Yeah. Yeah, old houses were way more forgiving. It’s not like we have more leaks in today’s houses, it’s just that those leaks matter a heck of a lot more.

TM: Yeah.

BO: Yeah, that’s interesting. Okay, so tell me about insulation, and tell me about leaks, and all of that. So is this just a flashing detail problem or is this because there’s insulation, the leak becomes more like a sponge? Or why are these leaks such a big deal?

TM: Well, that’s a good question. And it’s not just flashing that has to be done, right? There are so many potential places for moisture to get in and to cause problems, but moisture really is a home’s worst enemy. It can come from the inside or it can come from the outside. And so, making sure that you’ve got all the flashing details done right, all the siding details done right, on the interior, you’re managing your humidity and your moisture properly. All those things are really important. But even if you do things right, there are some situations that are just a recipe for disaster anyways. So let’s say you have a house that you could have like a brick or stone veneer type siding, which is like a reservoir cladding. It basically, it’s like a giant sponge on the side of your house. That type of siding material will just hold moisture. So let’s say it rains, that siding is saturated holding onto all that moisture. Then the sun comes out, beats down on that wall, heats up that wall. And let’s say it’s summer time, we get hot temperatures here in Minnesota, so people have their air conditioning running.

TM: So, physics, so basic physics, moisture moves from areas that have more moisture to areas of less moisture, and also heat moves from warm to cold. So, what happens when you have sun…

BO: Wait, wait, wait, wait, wait, wait, wait, wait, wait, wait. It rises, Tessa, it rises.


RS: And it falls and it goes sideways. It goes in every direction.

BO: I’m sorry, I shouldn’t have done that.

TM: Heat moves from areas that are warmer to areas that are colder. And warm air is less dense than colder air. So cold air sinks and when that sinks, the warm air moves up. So you’re thinking about stack effect where in houses in the winter time in Minnesota, it’s gonna be warmer upstairs and colder in the basement, ’cause that warm air is rising. But think about a wall system, if you’ve got the sun shining on a brick wall that’s wet and that sun comes out, heats up that wall, and it’s, let’s say it’s cold inside, ’cause they’re running their air conditioning. Which way is the vapor drive now? Heat moves to cold, more to less. That moisture is going to want to dry inward from that wall cavity. Now what happens if you don’t have a proper weather-resistive barrier on the wall system or you don’t have a proper air gap for that moisture to dry behind that wall system, and let’s say you’ve got some sort of wood composite product like Buffalo board or Particle board, or OSB, behind there, that stuff is really absorbent. And that moisture can go right through that wall assembly. And then what do we put on the inside of our walls?

RS: We put a vapor barrier.

TM: We put a vapor barrier.

RS: It’s not gonna let it go through.

TM: We put plastic.

BO: So it stops right there.

TM: So have you ever seen mold on the back side of a poly-vapor barrier installation, like in a basement?

BO: Sure.

TM: Like in a walkout basement?

RS: Oh heck, yeah.

TM: Oh yeah. Almost, I swear, almost every basement that is unfinished that has the fiber glass bats with the poly plastic over it, I will be able to find mold somewhere behind that plastic.

RS: And, Tessa, I just wrote about that in my blog post…

TM: I saw that.

RS: The top five places to find mold. And I asked Vickie about it when we had her on the podcast, but I already had my list created.


RS: I was kind of asking Vickie to see how much overlapped with my list, and that was definitely one of them was basement… Walkout basements with the unfinished wall and the poly vapor barrier, and I just came right out and said, “This is just plain stupid.”


RS: The way we build houses, prove me wrong.

TM: Yeah I saw that. And you know what, it’s not even just walkouts too, Reuben. You can have that vapor drive inward on a full basement, like a foundation, too. When you’ve got a concrete block wall that’s in contact with wet soil.

RS: Yeah you’re right.

TM: And you, let’s say someone tries to finish off their basement and they do the fiberglass baths, and the poly over that there’s a good portion of the year where that vapor drive is also moving inward, and you can get moisture trapped behind that plastic too.

BO: Please correct me if I’m wrong but I always thought that subterranean vapor drive was always inward.

TM: You know, that’s a great question. It’s not. It’s variable. It can go both ways below grade. That’s why it’s so challenging to insulate properly foundations without having moisture problems.

BO: But I imagine for most subterranean and most below-grade applications, there’s a higher level of moisture content in that soil than actually in the house itself.

TM: Usually. I’m not an expert on that type of thing, actually. So Pat Hellman at the University of Minnesota, he does a lot of research on foundations and moisture movement. We should have him on this podcast, but he works with another scientist, Louise Goldberg, and they’ve been doing years and years worth of research on hydrothermal, how moisture moves through foundations basically.

BO: He has a great YouTube video.

TM: Yes.

BO: I believe it’s through NDSU, North Dakota State University or up north there.

TM: Cloquet is where their research facility is. I wonder if it’s…

BO: We can look it up.

TM: Yeah.

BO: And connect it over to this podcast, but it’s a fast thing, it’s 30 minutes of time and you’ll never see your basement the same way.


BO: So with that…

TM: If you wanna have nightmares about your finished basement having potential moisture problems, watch that video.

BO: No, no, no, no, nightmares. And one of the things I think most of us know the difference between old and new is there’s just a lack of insulation, which means a wall cavity has less of an ability to dry out if it were ever to get wet, bulk water or otherwise. But so, my old house from the 1940s has basically got no insulation, and it’s got a little bit, so it’s pretty forgiving. Tessa, in 2020, if you had to tell me what the ideal design of an exterior wall in our climate in Minnesota, whatever zone we’re in up here, what does it look like?

TM: So a perfect wall would have the insulation, and would have the water-resistive barrier on the exterior, and the structure would be inside the thermal boundary in a conditioned space. So it looks a little bit different, but you’d have your cladding, you’d have an air space, you’d have your insulation and then you’d also have your water-resistive barrier, vapor barrier, right touching that insulation on the back side of it. Then you’d have your structure behind that.

RS: So I know all these terms but I’m still having a hard time following. Just to kinda sum it up, the short version of what you’re saying is put the insulation on the outside, right?

TM: Yes. Yup. Protect your structure on the inside, keep it in… Right now, walls are susceptible to the temperature changes and humidity changes, but if you move that air barrier, vapor barrier insulation to the exterior, now your structure is going to be 70 degrees and 40% relative humidity year-round, all the time.

RS: Yeah, when you say your structure is gonna be 70 degrees you’re talking about not just the inside of your home but the entire wall assembly.

TM: Exactly.

RS: The drywall. The studs.

TM: Yeah.

RS: Everything is gonna be nice and warm.

TM: Yeah.

RS: And you move that thermal boundary right before your siding.

TM: Yeah.

BO: So I’ve heard this in the past and I can’t attribute it to anybody because I can’t remember who actually said it, but I heard warm wood is happy wood.

TM: Yeah.

BO: Is that true?

TM: Well, yeah, I think it’s a much more durable system to have that. And actually, some of the research for Building America, it’s a program funded through the Department of Energy. It’s a national program that basically is researching how to make houses more energy efficient and there’s a bunch of different scientists around the US that are doing all this research on homes on how to make them more energy efficient, but also, more durable and more healthy. And Pat Hellman is on one of these teams and they did research, and they basically designed a house that was built this way, with this type of wall system, where they used these giant OSB panels, these structural OSB panels, and they built the frame of this house by sticking all these panels together, and then they wrapped that in a weather-resistive barrier like grace perm-a-barrier, it’s a waterproof membrane, self-healing membrane, and that makes the house really air tight but also protects the wood from any sort of exterior water intrusion. Then they attach the rigid foam insulation to that, and then they attach the cladding to that.

BO: Okay, so I’m trying to visualize this, just what you said. We have studs, we have sheathing…

TM: No studs.

BO: No studs.

TM: This house didn’t use any studs.

BO: Okay. So that’s where the structural panels came in.

TM: Yeah.


BO: No, we do not wanna confuse SIPs with what…

TM: It wasn’t a SIP. Yeah, it was something…

RS: It sounds like you’re describing a sip. I don’t understand the difference.

BO: It was a built-on site panel.

TM: It’s a structural panel that they… I can’t remember the name of the company that manufactures them, but it doesn’t come with any insulation or anything attached to it, it’s just the OSB panel.

RS: Okay. All right, got it.

TM: So they built the house with those panels first, wrapped it in a self-healing waterproof rubber membrane, and then attach the installation to that. So different from a SIP but…

BO: So I imagine you just answered this question but I’m gonna ask it anyway in case other people have a tough time like I do visualizing. I imagine these houses that are built with sticks, they lose a bunch of the racking support or strength that would come with having that sheathing right there, right? So if the sheathing is on the studs and then the installations in the stud cavity, it feels like a more rigid construct than if you have rigid foam as the sheathing.

TM: Well, with the system I was describing, those OSB panels, they put two of them together, and I think the wall was at least an inch thick, maybe an inch and a half thick, of solid wood. And they’ve been doing testing on these houses, engineering. And it turns out these houses are even more strong than a standard stick frame house would be.

BO: Yeah. So that’s what I always feel about these new houses. I feel like there are a lot like airplanes. When a tornado comes through, you see the damage and there’s things all over, they’re missing and they’re gone and where… My neighbor tried to tear down their garage last summer and literally drove a Bobcat through the wall…


And the thing didn’t fall down.

RS: Oh, you know what, on that just personal story. I grew up doing construction with my dad. I remember in junior high my friend and I were tasked with tearing down a garage. My dad dropped us off, we got the whole day, we had to tear down this garage at this house that my dad owned, and we cut out all the studs. No more studs, garage was still standing. It was the stucco keeping everything up.

TM: Wow, yeah.

RS: Structural stucco.

TM: Structural stucco.

RS: Exactly.

TM: Yeah. Well, the other thing I didn’t mention, too, with this design of having your structure on the inside and moving that water barrier and insulation to the exterior, it also eliminates all of the heat loss you have through thermal bridging in a normal framed house where you’ve got a stud every 16 inches or 24 inches, where you don’t have any insulation in the wall at that point so you lose heat through that wood framing. Wood framing takes up like 25% of the wall. So if you think you have an R-20 wall, well reduce that by 20% because of all the wood framing that’s in there.

RS: Yeah, wood is a horrible insulator.

TM: Yeah.

BO: Well, and so now I’m thinking back to the limited amount of building construction experience that I have. And we would always put the headers in over these windows and it felt like that was just a poor insulation construct.

TM: Exactly, yeah.

BO: So what does a header look like in this panel house that you’re referring to?

TM: It doesn’t need a header because the panel itself is enough, it’s the structure.

RS: Oh, of course. Sure.

TM: So, they cut out holes in the panel, you don’t need to add anything else to it.

BO: So then are these… I imagine these panels are the full length of that wall and they’re kind of overlapping and…

TM: I think these panels are like 8 feet by 20 feet.

BO: Oh my goodness.

TM: You need a crane to lift them into place. They’re massive panels, really heavy.

BO: Okay. So maybe if you’re thinking of all these big warehouses that you see and the span creep that, it’s sort of along those lines.

TM: Yeah. Yeah.

BO: Okay. Interesting stuff.

TM: The hard thing is, though, these panels are so big it makes it difficult to have a house that has unique design to it. A lot of people these days, they wanna customize their house, they wanna have cool little architectural details, they wanna have bump-outs, cantilevers, bay windows, whatever.

RS: I call those magnets for water intrusion.

TM: Exactly, yeah. No, from a building science perspective, every time you bump out that building envelope or change a plane of a wall or whatever, it’s one more thing where water can get in or siding insulation could go wrong where it’s just a higher risk with that type of design. The more complicated, the higher the risk. But people don’t wanna buy just a plain, boring box, unless you’re building scientist like me and I’m okay with it. [laughter]

BO: Tessa smiles.

RS: I’ll take one too.

BO: A plain, boring box and she’s got a big grin.

RS: With big overhangs, right?

TM: Yes, big overhangs, yeah, great orientation. Energy-efficient? Yes.

BO: Awesome. Well, we’re out of time for this episode and we didn’t even get to air comfort or how do you say it, indoor…

TM: Indoor air quality?

BO: And comfort.

TM: Comfort, yeah.

BO: Yes. We’re gonna run right into Episode 2 on new versus old and we’re gonna talk a little bit about just the differences in these houses and how they feel. You’ve been listening to Structure Talk, a Structure Tech presentation. Thanks for listening.