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Andy Wojtowski

PODCAST: Patrick Huelman, Tessa’s professor

The gang is super-excited to finally get Patrick Heulman, a leading building science expert, on the show! We’ve talked about having him as a guest for a long time and now that we’re temporarily recording our podcasts from our homes, we were able to get Pat on the show. He’s an Associate Extension Professor with the University of Minnesota and works on several other projects as well.

The show starts out digging into Pat’s background and then moves onto the importance of considering a house as a system. Pat talks about how air exchangers first began making their appearance in Minnesota in the early 90s, and Pat also talks about “The Cliff”, the benefits of insulation at the exterior of homes, and perfect wall systems for homes.

The show ends with Tessa sneaking in a question about one-and-one-half-story homes.


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.

Pat Huelman: So the way I describe building science is it lands kind of a nice little niche in between architecture, engineering, and that could be mechanical engineering and somewhat structural engineering, material science, and construction management.

Bill Oelrich: Welcome, everybody. You are listening to Structure Talk, a Structure Tech presentation. My name is Bill Oelrich, alongside Tessa Murry and Reuben Saltzman, the wonderful cast at Structure Tech Home Inspections. And we’re here to talk today… I’m very excited about this. Our special guest is Pat Huelman from the University of Minnesota. And we’re gonna be talking about building science and cold weather building and all kinds of different stuff. But let me take a second here and introduce Pat officially. Pat, can you tell us all about yourself, please.

PH: Yeah. I work at the University of Minnesota. I essentially wear three hats. So land grant institutions are known for research, teaching, and outreach. So one hat is I’m associate professor in bioproducts and biosystems engineering where I teach building science. We have a building science program… Curriculum there. I do research. My primary research for the last few years has been with the Department of Energy’s Building America program. But my primary hat, if you will, primary function at the university is I work with the University of Minnesota Extension. And what that really is all about is pay most of my salary. And for that, I do applied research and education to the masses, taking what information we know about buildings and building performance, building science and getting it out to people that can use that knowledge generally focused on the building profession. Too many consumers out there to do that one at a time. So we’ve chosen to work with builders and subcontractors, suppliers, to get that information out.

BO: Outstanding.

Reuben Saltzman: And you do get that out to people. Pat, I met you… I don’t remember when, but the first time I really got to sit through your teaching was when you taught an all-day seminar for us, home inspectors, several years ago. And we all just went, “Wow, we need more Pat. This guy is awesome.” It was such good information. And your name has come up on our podcast, what do you guys think, maybe about 73 times [02:25] ____ getting you on this podcast.

Tessa Murry: Yes.

RS: We talked about you… Well, Tessa especially talks about you a lot…

TM: All the time.

RS: So we’re glad to have you on the show.

TM: Yeah.

PH: Well, I’m glad to be here. This is fun.

BO: Good. Tessa, why don’t you go ahead and do full disclosure here and give the background of how you know Pat?

TM: Well, I know Pat… Everything I know about building science came from the University of Minnesota and the building science program that’s led by Pat. And so I went to the University of Minnesota and graduated with the degree in residential building science and technology which… It was in the Bioproducts, Biosystems Engineering Department. I don’t know what it… What is it called now, Pat?

PH: Just building science and technology. We dropped the residential.

TM: Okay, building science and technology. And it’s a pretty small program at the University of Minnesota, but took some amazing classes taught by Pat which led me down this road of home performance, energy efficiency and doing home inspections today and doing a lot of teaching and training for other inspectors and real estate agents and all of that.

BO: Awesome.

TM: I owe it to Pat to where I am today. So thank you, Pat.

PH: You’re more than welcome. You’re an extension of my extension.

TM: There we go. [laughter] Yes.

BO: It’s fair to say then this is the mentor and the mentee. It’s like Luke Skywalker and is it Obi-Wan Kenobi, is that the relationship that we’re working with here?

PH: Oh, boy.

BO: So Pat, tell me, you’ve been doing this a long time. How did you happen into building science? What was your background before? And I know there’s some real pioneers in this and I consider you to be one of the pioneers in building science. So tell me how you got into this business.

PH: Somewhat accidental. There certainly wasn’t a discipline or a field of study called building science when I was in college. So I took things like environmental design, environmental studies. I focused a lot of my undergraduate and graduate work in energy and energy efficiency, how buildings interact with their environment. And I took architecture and some engineering, some landscape architecture. So it was always around how buildings work and in essence that’s what building science is. So I would say what you find is while there are lots of building scientists, few were trained in that way. They just became building scientists due to their interests and their background in things like thermodynamics and moisture control and buildings, materials, whether it’s wood or other materials. So the way I describe building science is it lands a nice little niche in between architecture, engineering, and that could be mechanical engineering and somewhat structural engineering, material science, and construction management. And so that’s really where it’s housed and it’s all about how buildings perform.

PH: In the US, building science has become synonymous with heat, air and moisture flows in buildings. We call HAM. And that’s not necessarily true worldwide. In Europe, building science is called building physics, in fact, and has a much wider connotation including sound transmission and light and fire, other life safety issues. In Canada, it has a little combination or flair of that but it’s referred to building science. And quite frankly, that’s where the discipline or thoughts leading to where we are today in building science came is from early pioneers in Canada. And there were certainly pioneers here in the United States too in the ’40s and ’50s and ’60s that really launched the idea of building science, building performance.

PH: But I started out looking at energy primarily. And then I realized all the things that happen when you make buildings energy efficient, some of them good, some of them not so good, whether that’s moisture control or indoor air quality or other concerns. And so then we realized we had to take a holistic approach, systems approach. When I came up here in 1988, my interview presentation was the house as a system. And this was such a novel concept they actually gave me the job.

TM: Wow. That’s so cool.

PH: But anyway, we realized _____ something that was much more holistic in its approach, both from a physics perspective or a science perspective, as well as engineering and application. And that’s really what building science has become.

BO: Very good. So where were you before?

PH: So I was at Iowa State, and I worked for the energy extension program there. And I came out of school, my undergraduate degree, focused on energy. Then I went to work for the Energy Extension Service at Iowa State, and that started to broaden out into a couple other areas. I led the indoor radon project with a colleague there, looking at radon issues in Iowa at that time. I then started the Iowa Quality Housing Council, and I was really trying to work with builders to build towards high-performance homes. This was in the ’80s. Ventilation started becoming a very popular topic, rainscreens, things like that, which we still talk about and struggle to get into the market today. [chuckle] But anyway, that’s where I spent the time. And then I came to University of Minnesota in 1998 to join the Cold Climate Housing Center at that time. It’s now where we just call it the Cold Climate Housing Program.

BO: So at some point, people in your industry realized, “We had to connect this idea of HAM with the actual boots on the ground constructing these houses.” Was there an aha moment where we have to somehow get in the room and have a conversation with everybody, this holistic approach that you’re talking about? Or how did that fall into place?

PH: Well, I think there probably were little light bulbs along the way. I can’t think of the big aha moment, but I was, like I said, I was trained, if you will, and thought in energy. I thought in BTUs and kilowatt hours. And as I designed a number of houses in the late ’70s and early ’80s, and you start to get patterns. I was starting to think about, “Well, ventilation has to be an important aspect of building houses that are much tighter, right?” And then you would see it, whether it’s window condensation or other issues, mold growth on top plates. So then, when I came to University of Minnesota, I came 1998 into the Department of Forest Products. Why there? Well, most of our houses were built out of wood, and lo and behold, wood has certain moisture issues associated with it. And houses that we were building were having more and more moisture problems.

PH: So my head spun right around from energy focus to, “Well, let’s think about how we manage moisture in these buildings, whether it’s inside the structure or in the wall cavity or up in the attic.” And then very naturally, out of that became a concern for indoor air quality like, “Okay, now, we got the shell thing figured out or the enclosure, the envelope. We’ve got some of the other efficiency things sorted out. We’ve got ventilation now or moisture control in place.” But we still didn’t have the indoor air quality picture totally solved, if you will. And so, that really drove in a whole another round of, “Well, how do we build these high-performance homes that provide high-quality comfortable space, but also healthy space or healthy indoor air?”

BO: Sure, what year would you assign to that transition?

PH: The early ’90s. I think what had happened was the ’80s… Well, the energy crisis got me involved in this in the first place in the ’70s. In the ’80s, we started exercising our control, if you will, on the energy through better insulation, air sealing and some of that. Again, then the ventilation came right in behind there. But by the early ’90s, we realized we were building from pretty decent structures in terms of insulation and air tightness, but they were inadequately ventilated. And so by 1991, I had started a group called the Residential Ventilation Task Force here in Minnesota to look at how we are going to bring ventilation into a new construction in Minnesota. And that’s why, I think, started to come into the code, and then we developed what’s called the Residential Ventilation Standards Group. And by 1994, we had in place, basically, a pretty solid approach on how we’re going to mechanically ventilate our houses in Minnesota. And then by 2000, that became a code minimum, if you will. Not saying it’s perfectly done today, by the way, but the foundation is there and the fundamentals are in place. And certainly, our houses do have some type of ventilation. It’s just maybe not the best or the most sophisticated approach.

BO: Does perfection in houses, can we use that in the same sentence? So there’s a degree there is you always have some variability that it’s imperfect in some way or another, right?

PH: Absolutely, yeah. And so I think the great chase of all of us and certainly, building scientists, everyone would think that we’re trying to chase the perfect house. And really, what we’re trying to chase is an understanding of how houses work so that we can build better houses, and we can build houses that have some forgiveness or tolerance. I use the term “robust” a lot. I like the idea of something that’s robust. And so, we’re not trying to hit perfect; we’re trying to hit something that’s robust enough that it will provide a high level of efficiency, a high level of moisture control and building durability, reduced maintenance, long life of our building materials, and provide healthy indoor environment for the occupants. So I think robust is a better strategy than perfection ’cause one, I don’t think it’s really possible. And two, in the end, it has to be implemented and executed by a whole lot of hands that aren’t going to understand how to achieve that perfection.


BO: Yeah, you can draw out the directions perfect, it’s just does somebody read them and actually do what you say? I could ask a gazillion questions Pat this would be, the next seven hours, I would not stop. I would just keep firing questions at you, but I don’t wanna monopolize this entire conversation. So Tessa. Reuben, feel free to jump in here at any time. [chuckle] I think I’m fascinated… And so Tessa, just raise your hand, tell me when to shut up, but I’m fascinated by the change in materials from old-growth to these engineered products. I sit next to a mill right now in International Falls that makes an engineered product that goes into a lot of houses built. Buffalo board, we’ve seen it all over the place. And you talk about engineered materials and durability, and then you throw in this cocktail of moisture and all of that other stuff. It just seems like this is a math equation that has so many variables. How do you begin to isolate them and solve to make sure that you’re not changing one thing to the detriment of the other?

PH: Well, that’s an excellent question. And clearly, our building materials have changed. Clearly, our wood building materials have changed, and they have moved a long ways from solids on old-growth lumber. And we don’t have that and can’t raise enough of that, so we aren’t going back there. We’re going to use wood in a more efficient manner, let’s say. In doing so, it has different properties. So it’s back to the material science, but then, how does it apply to buildings? And lo and behold, it just simply behaves different when it’s pushed a bit, if you will, or exposed to too much moisture. So it comes back to it’s not a material problem, it’s a moisture problem. So we have to manage moisture better. And so…

PH: Very interesting that this became so evident in a lot of things. I just spent a long time on the phone with someone that has a mold problem in their home, and I kept trying to express to them, it’s not a mold problem, it’s moisture problem. You’ve got to go after and find the moisture problem, then you can clean up the mold and it’s gone. So same thing would be true for the wood. We’ve just gotta simply treat it better. Understand its change, understand how that impacts its performance, and understand how we might have to treat it differently when we put it into the building. So I think, we’re going to see a lot more wood in buildings for a lot of really good reasons, but I also that the same fear, let’s say, CLT cross-laminated timber has become very popular and it’s using full solids on lumber, but put together in plates, if you will and it makes sense. It’s a renewable resource, it’s a low energy input, it can be durable if treated properly, and we can sequester a bunch of carbon into our building.

PH: So and it really come backs to me is just says, “Yeah, we just need better building science to use the materials properly and put them in the right place where they can do the job and train the trades to respect and treat the material and implement or execute it properly. So I think about building performance, it’s like you said, there’s design, how does it get designed and specified? We don’t do a good job of that. There’s a lot of unknowns when that piece of paper gets turned over to the trades to do their work. And the second part is the execution. How does it get executed? And some of that’s by training and old wisdoms or other things that come along, and that’s not necessarily adequate with some of the new technologies, or new materials, or the new designs are being used today. Sometimes we also forget is occupant interaction and the occupant role and how the building is operated and maintained. So all three of those have to have building science understanding and information and education built into them to end up with the high performance building that we want at the other end.

RS: Reuben here, I’m gonna jumped in for quick second and ask you ’cause you said we’re gonna be seeing a lot more wood in our buildings. And it’s something I joke with a lot when we’re teaching classes about how newer buildings have a lot less wood. Just because we’re not over-engineering these anymore. So when you say, we’re gonna be seeing more wood, I assume what you mean is that we’re not gonna be seeing more wood in the same building you’re saying, we’re gonna be seeing more building with wood in general, right?

PH: Right, yeah. We’re gonna see more wood-related products.

RS: Okay.

RS: People look at the energy intensity of some of the alternatives, whether it be concrete or steel or whatever. And while they look attractive and they don’t degrade the same way, they still have other issues and they’re expensive. The wood’s relatively inexpensive material. I’m just saying, we’re gonna see more wood or wood fiber into our buildings for a lot of other factors and forces in the both economic and environmentally.

TM: Just wanted to clarify, very good.

PH: Yeah.

TM: While I got the mic just for a quick good second. One other thing I gotta ask you about 10 minutes ago, you had mentioned changes in buildings right around like ’91 there’s some changes or there was basically a standard that came out for ventilation. And I seemed to see that’s about when we started seeing air exchangers in homes was right around that time. Can you just tell me what did it require right then?

PH: I wanna back up and introduce a little concept or idea. I like to use the metaphor of the cliff. And what has happened over time is we’ve taken our houses and we’ve taken some of the robustness out. We haven’t paid attention to certain things that are important and we’ve moved these houses closer to the cliff. Now the cliff is a metaphor for a failure. It could be a structural failure. Those aren’t all that common, they happen, where something literally falls over the cliff, if you will, or falls down. But this is more other performance metaphors, whether it’s combustion, safety and indoor air quality problem, a mold problem. The building enclosure is deteriorating. The attic is full of frost and mold, or we have ice dams that just simply overflowth. So the cliff is a metaphor for this performance failure. And we’ve moving houses towards a cliff for quite a while. We started in the ’60s and ’70s and ’80s. By the ’90s, we were awfully close.

PH: The other thing that happened in the ’90s, of course, was a massive boom. You could build anything, you could sell anything for top dollar. And so, we had a massive influx of houses and buildings in that era, that maybe somethings were missed in the design and/or the execution. I’ve always referred to as the x-factor, the execution factor, but it was becoming apparent the ventilation was critical. So in 1991, the code started to make a nod to ventilation. And by ’94, it basically said in the code, if you build a tighter house, thou shalt have ventilation, mechanical ventilation. And it kind of implied, if you build a leaky enough house, you don’t need one. Well, that’s flawed building science, but that’s what it said. Some of those houses that I call kinda tight, is not alright, ended up being at the edge of the cliff. So by 2000, that was clearly recognized that we needed mechanical ventilation. But meanwhile, the market itself had gotten pretty good foothold on air to air heat exchangers at that time the term was used. Now, we call them heat recovery ventilators, energy recovery ventilators.

PH: We had a strong market in place in Minnesota by 2000. In 2000, the code came in and said, “You will all have mechanical ventilation, but we’re going to allow exhaust only ventilation to continue.” I even was supportive that idea at that time, just so that we could get it instituted and accepted and codified, if you will. Well, unbeknownst to me all heck broke loose. So I always say, good intentions, sometimes, don’t go the way you think they might. And the market went to a lot of exhaust only ventilation and the market for air to air exchangers and heat recovery ventilators, etcetera, fell way off.

RS: Pat, if I can just jump in for a quick second, I’m gonna do what Bill always does and explain these terms that our listenership might not know. ‘Cause just so people understand when we talk about exhaust only ventilation, we’re talking about a bath fan that runs 24/7, and it’s usually gonna be… For a long time, Panasonic had the market cornered, they were all Panasonics ’cause they’d make these fans that would run 24/7 they’d be silent, you wouldn’t even know it was going and it’d be like what? Like 40 CFM or something like that, it’d be a little over.

PH: Higher in some cases to…

RS: Yeah, and sometimes you’d even see it in a hallway upstairs, it’d just be in a second floor hallway and it would run non-stop. That’s what Pat’s talking about for exhaust only ventilation.

PH: So you’re exhausting the air out of the building and you’re relying on leakage somewhere for the fresh air to come in and replace it. And it does put the house under a slight negative pressure. That’s how it sucks the air in then it needs to replace that air with the “fresh outside air.” It’s not the grandest system, but we had made sure that the houses had sealed combustion for the most part, we weren’t going to… The negative pressure wasn’t gonna cause a combustion problem. The code did start to adopt some radon resistant strategies or techniques in the appendix, so we felt like radon might… If it was a problem, could be mitigated easily. So there was some thought that this is gonna be an okay interim strategy. But I think everybody knew, sooner or later, we had to move… In a cold climate, quite frankly, that has a very hot humid summer climate, that sometimes we fail to address, we were gonna have to move to more of a balanced heat recovery ventilation system. And then, in 2015, the code said you will have balanced ventilation. So now, we got away from the exhaust only side, and it was gonna be balanced, but heat recovery was not required. Well, the reality is, a balanced system with no heat recovery is an oddity. It’s a… You’d have to make it up as you go. And so, clearly, in 2015, the market for the energy recovery ventilators, heat recovery ventilators, came back strong. And again, the market now is predominantly that type of balanced ventilation.

TM: Okay. Pat, I have so many questions that I wanna ask you. But one of them would be, what has been your favorite research subject over the years? What topic, or what thing have you learned a lot from, or has surprised you, or that you just think is fascinating?

PH: Well, I’ll answer that in two parts, and I’ll keep them separate. The first one is just recognizing that the order matters. And so this idea of the cliff is an important backdrop here. But then we realized, well, what order we do things matters. And so, the order that the market chose was, well, let’s chase energy first and then that caused moisture problems. Well then, let’s chase water control and water management. And in doing both of those, we ended up with an air tightness problem, if you will. And then the air tightness, and I’m gonna put quotes on “air tightness problem”, that caused us to need to start thinking about ventilation. And at one point, that wasn’t methodical and thought out in that way. That’s just how the market did it.

PH: But all of a sudden, that’s an aha moment like, “We’re doing this backwards folks.” And people would ask questions about, “Well, I have an existing home. And should I put ventilation in?” I said, “Of course. That’s where you start, always.” So then when you realize if you ventilate first, and sealed combustion, of course, is in there, I should say, combustion safety was the last thing we went after. But if you do combustion safety, then you do ventilation, and then you do air tightness, and then you provide water control, then you can insulate all you want, make your heart happy. It’ll all work. You’ve made no big steps towards the cliff and probably have made several steps away from the cliff. And so that order was, and that sequence, was an aha moment that was really big for me.

TM: Pat, it’s so fascinating to hear you say that because a big aha moment for you, but we are still trying to teach that to not only homeowners, but contractors and people that work in the energy world too.

PH: Oh, totally. So where did I learn it? I learned it in new construction. Bear in mind, I gotta be delicate about how I say this, but there are a lot of things we did that we knew we shouldn’t be doing, or we knew what the outcome would be, and were trying to caution folks, “Be careful.” But Joe Lstiburek said it once, and he said, “The building industry is a discovery industry. They find problems through discovery, or discovery is how they see problems.” And so they aren’t going to fix a problem they don’t see or haven’t discovered yet. And so it was just… That’s just how the world worked. So we had to go through each of those five levels, combustion safety, ventilation, air tightness, moisture control, and insulation, in unfortunately, a series of events that we discovered didn’t work well. And then we turned it around went the other direction.

PH: And I said right away, “Well, we’re gonna do this again with our existing buildings.” People are gonna go out there and they’re gonna save energy, they’re gonna put insulation in, and they’re gonna want to air seal their building ’cause it’ll save energy, and then they’ve got a moisture problem. Then they fix the moisture problem, and all of a sudden, they’ve got a ventilation problem, and then they see they have a combustion safety problem. And so why would we do that? And weatherization learned that lesson the hard way. And they realized they had to turn things around. I don’t know they do exactly the sequences as I had mentioned. And then, all of a sudden, that became a guide for, “Okay, before we take this step, where does it fit in the order of things, and will it move us towards the cliff?” And again, I agree with you, it sounds so simple. It’s not as simple as it sounds, and it certainly isn’t universally understood or accepted.

TM: That reminds me when I worked for the insulation company, a home performance company for five years, one of the hardest things to explain to a homeowner was, “Okay. Well, yes, we’re gonna improve the energy efficiency of your house, we’re gonna air seal the attic, blow in insulation. But first we need to replace your water heater, that’s atmospherically vented, with the power vent water heater, and we’re gonna have to add some more ventilation in your bathrooms.”

PH: Yeah.

TM: And people are like, “What? I just hired you to blow in insulation. What are you… “

BO: That’s not at all what I hired you for.

PH: Yeah, exactly. Yeah. You just told me seal it up. And then you’re gonna tell me to turn on a fan. Come on.

TM: Exactly, yeah. So it really is looking at the house holistically and how all these pieces fit together. There’s lack of understanding of that.

PH: Yeah. The second answer to that question was really as I developed my understanding of moisture, moisture management, and building enclosure systems, the energy part was simple. Just insulation and air sealing. That was an easy part. Managing moisture across the building thermal envelope, whether it be liquid water or vapor, that was much trickier. And the next aha was this idea of the perfect wall. Again, this is a term that was popularized by Joe Lstiburek from Building Science Corporation, but he is really quick to give credit to the early Canadian work, where they had developed this concept very early on in the ’60s. And it was written about in their, what’s called the Canadian Building Digest, CBDs. But it came around again and we saw lots of different iterations to this. I mean, you see…

PH: We had a term called ____ and there was outsulation. And there was PERSIST, and PERFORM, and you name it, all kinds of acronyms around this single concept. And the concept is this simple, you have to put the structure of the building inside where it will always be warm and dry conditioned. So what’s the most important thing in your house, your structure. That determines ultimately, it’s life expectancy or life span. So you put that inside. And then we wanna control four things. We wanna control water, heat, air, vapor. And we call those the four control layers. And so we put the four control layers to control water, heat, air, and moisture on the outside of the structure. And then a really important piece here is we put on a cladding system, a roofing system, could be a foundation system that provides drainage and drying. And even under our slabs. We put a large layer of aggregate that provides drainage and drying. So if we wrap our structure with those four control layers and the ability to drain and dry, it’s gonna work every time, everywhere, every place, every climate zone. It is simply so simple.

TM: It’s the perfect house, the perfect wall.

PH: Yeah, the perfect wall.

TM: Yeah.

PH: Now, we can mess it up in design by specifying perhaps the wrong material in the wrong place, or have a sequence issue. Or we could have trade issues that don’t install things proper, but on paper this works so well. And so that was a big professional aha for me, and that really started to drive my looking for how do we put together buildings differently. ‘Cause all of our buildings have integrated the structure into the insulation. And then we put an air barrier on the inside or outside or both. And then we control vapor on the inside of course, in the winter but it has to be controlled in the summer. And then we end up with a window leak, where the water is in the middle, and has no opportunity to dry whatsoever. And we just messed up the whole thing. So that’s why a lot of the work has really been driven by trying to find a building system that’s relatively quick, easy, relatively inexpensive to do, that will provide a structure for the house. It’ll hold up the roof, and keep the snow up, and resist wind loads.

PH: And if you’re some place where you have seismic or whatever that structure is intact, and then peel on the layers of the onion, the control layers on the outside, and then make sure you drain and dry. And it’s just so elegant. The control layers, and the change in the cladding approach, or drainage for the foundation, or venting systems for the attic or roof are more expensive. And so again, it drives it back to, can we come up with a better structural approach to our buildings that gives us the flexibility and the finances to put the right coat on the outside, the right set of control layers on the outside?

TM: So Pat have you built houses this way?

PH: Yeah, absolutely. We have looked at a number of things. A big project that we’ve been working on now is… Basically, 2000 was the idea of plate construction. So could we replace the stud framing with a panel or a plate, a diaphragm if you will? So a lot people are familiar with diaphragms that move load, like a floor diaphragm or a roof diaphragm that moves loads around, and are structurally integral and supportive. And could the wall be done in a similar way? And obviously in the past, the walls were mostly to hold the roof up, and then we stiffened them for shear and wind. But could we use plates or a diaphragm to do that same work? And sure enough, yeah you can. And you can build relatively thin walls, a couple inches thick in this plate fashion that provide structure for gravity loads, and wind loads, etcetera. So that was gonna be then our entree point to build the structure different.

PH: And there’s no other way to insulate that of course ’cause there isn’t a cavity. You’d insulate on the outside. So we did several iterations of that, starting in the… Around the 2000s. And then by 2014 a company here, a developer, a builder, and another company teamed up to build the… Seven of these houses. And that was then the impetus for us to get a DOE grant to basically study this system and validate it for the market. Which we have done, we’ve just completed that report. And one of the critical elements as you might suspect is the structural behavior of this panel or plate design. And now we are just starting a second DOE project to basically get the structural engineering that we need to support the building system that we need to support the exterior control layers or the perfect wall.

TM: It sounds like a pretty cool system.

PH: Yeah, it’s fun. And there are hybrid versions of this. There’s other ways to implement what I’ve kinda just suggested in terms of the perfect wall. There are ways we can use other building systems, we could even use stud framing, say like two by four stud framing. You also need to go more than that. And again, provide our structure in a maybe more typical or an old-fashioned approach, and then put the control layers on the outside. The only part of that is, it does get thicker. But we can execute the idea of the perfect wall in just about any structural system that you can come up with.

TM: Pat, I know you built your own house back in the ’90s, right?


PH: Yeah.

TM: If you were to build your own house now, would you use this panelized system?

PH: I would either use the panelized system or a hybrid version of it that we’ve been working on. Yes, absolutely. I have the classic two by six wall that has in fact built right on the outside, International Falls, I’m sure. With several layers of house wrap for water management, as well as some vapor control, that was necessary because I have polyethylene on the inside which I haven’t recommended since 1999. And yet it works beautifully in the winter, it struggles just a tad in the summer. It’s not a failure, I’m not close to the edge of the cliff, but there are some issues that… In terms of summer moisture, it just aren’t managed the way I’d like. And more so if I were to have a window leak or some kind of penetration, the wall simply wouldn’t recover very quickly. So I’d absolutely move back to either a hybrid or a panelized approach with the exterior control layers.

BO: So Pat on a follow-up to the perfect wall system. Is it necessary to have the engineered products to create that type of structure? And do those engineered products… They obviously give you the flexibility to make these large panels, correct? And then…

PH: So right now we’re using OSB as our panel. That’s not because it’s the only approach, you could use plywood. It’s just that the OSB is being made… In this case, it’s a very highly engineered, industrial, high-strength, high-test OSB that’s an inch-and-an-eighth thick and comes in panels that are 8-foot-wide and 24-foot-long so it’s really being done because of the availability of that at a very affordable price. But there could be other things that certainly could be used here. People worry about the OSB, they go, “Oh, moisture. Moisture, moisture.” “Danger, danger, danger.” Well, it’s on the inside of your house in no worse shape than your floor or your coffee table or your walls and so it is, in that sense. And it’s protected by a very intense, intentional air-water vapor barrier, fully-adhered membrane to the outdoors. Now, there are issues about off-gassing and some other things that come along with adhesives and, of course, we’ve paid attention to that and you wanna use a product that is very stable, in that regard.

PH: But, I talk about CLT. Well, what if somebody says, “I don’t want engineered lumber. I like real wood.” You could put up a CLT wall, it’d be a little thicker and it’d be all [32:56] ____ lumber with some glue, of course, between the pieces. It’d look gorgeous and it’d work fabulous; it would just be incredibly expensive.

BO: Sure, and these super structures, when you create a wall like this or a structure like this, are they… I’m imagining an airplane that’s incredibly strong in the first position that you build it. But if you go start cutting holes in it and try and expand or add on to this, are there issues with that later on if people wanna increase the size of the building?

PH: Sure, yeah. And the plane is really a good example, it’s… We’ve referred to it, I called it plate-like or diaphragm-like, but it’s really a monocoque construction. So if you think of a plane or you think of a race car that just went through the worse wreck in its life and the cage is totally intact with the driver inside, that’s essentially what this is all about. And yes, you do have to be careful where you put the penetration site with the penetrations, originally, and then certainly, if somebody wants to retrofit it, they don’t just go in and say, “Well, I wanna put on an edition here,” and cut out a 8-foot tall by 12 or 16-foot piece of the wall and put on their addition. So yeah, there are certainly limitations, engineering-wise, and that’s really what we’re trying to understand better with our current project is how many times can we perforate this plate and still maintain the structural integrity that we need?

TM: A funny story… Pat, I remember when I was doing some blower door testing on those panelized houses just to measure how airtight they were and they were the tightest houses I’ve ever tested. I remember turning on the kitchen hood vent and just having the front door just slam shut behind me ’cause they were just so airtight. You’d turn on that fan and it’s trying to pull in replacement air from somewhere.

PH: Yeah, there’s another “Ah ha!” moment, right?

TM: Yeah.

PH: So, to build houses of that tightness… These are tightest houses, as a pool of houses, the tightest houses probably in the country. And interestingly enough, nobody was running around on the job site with caulk guns, foam guns, cans of foam, trying to achieve that. We see builders out there today trying to hit three air changes per hour at 50, that’s a inside term for tightness, but… Or two air changes per hour. We believe the house probably should be closer to one air change per hour and they’re running around just going through all kinds of interesting exercises to try to achieve that. And then here’s a building that by the nature of how it got built, is that and it was half of that. It’s a half air change per hour.

TM: Yeah.

PH: And so that’s back to, “Can we be smarter about our design and our goals,” and the goal is to be airtight… Put these panels together with this full-adhered membrane and I’ll be darned, it’s tight, except for what little bit of leaks we get at windows and windows are in rooms where people are… Life is good, except there was an “Ah-ha!” Turn on the range, we had too much negative pressure. Turn on an exhaust-only ventilation system would be too much negative pressure, so it had to be balanced mechanical ventilation. We had to provide make-up air for the range hood. The clothes drier now is running for three or four or five, six hours constant on the weekend, causing extreme negative pressure.

PH: So that introduced for us now an unintended consequence. It was predictable and predicted, quite frankly, but now we have to put in an intentional make-up air system and so you talked about the homeowner that you were trying to sell insulation or air sealing to with a little ventilation fan. Now try explaining to somebody, “Well, we just built you a building and now you’re gonna buy this really expensive make-up air box because it’s so tight.” People have to be able to break apart the idea of the tightness of the structure and the air that’s needed inside, whether it be for make-up air or for healthy indoor air. They’re two separate things and once you have an airtight structure, it’s very easy to provide good, quality ventilation. And it’s very easy to provide make-up air because it’s predictable.

TM: As long as it’s maintained properly, right?

PH: Well, there you go… That’s the third leg. Design, execution, and operation. Yeah, and I think we are still failing to get our homeowners in a proper place for the operation side of this, unfortunately.

BO: What possibly could go wrong? Pat, we could spend 20 hours of constant questions; there’s so much to peel back here. But, thank you. We kinda have to put a wrap on this episode because there’s just… Where else do you break in and say, “Okay, time out”? But this has been fantastic, it’s just… I wish every homeowner would sit down and listen to this and just try to understand how a house performs and then the next time they have a friend or a dad or somebody who wants to help them fix their house, they say, “No, no, no, no, no, no. We need the contractor who understands what Pat just said and those are the only people who can work on my house.”

RS: A house is a system.

PH: A house is a system and here’s the tough part, quite frankly: It is a system and you touch something, it probably is going to affect something else. So your job isn’t just to go in and say, “Oh, you need a bath fan,” and say, “I’ll put that in for you for X-amount of money.” Your job is, “If I put this bath fan in, what else could happen?” And that’s easy conceptually. You’re gonna create some negative pressure, you’re gonna have some coming in, whatever, and it’s probably not the end of the world. It probably didn’t move you very close to the cliff. However, you do need to answer the question, “What else could happen if I do this?” And that’s the trickier problem, to be real honest. And especially in existing homes is, “Let’s move that up to a range hood.”

PH: They want a new kitchen, they’re gonna put in a range hood. You go, “I know how to do that.” And you go, “Well, are you gonna make sure it’s vented to the outside? ‘Cause that’s the whole point is to get rid of the gases and the particulates and orders and get them to the outdoors.” “Oh, of course. Yeah.” Okay, so now I have a vented range hood and it’s gonna backdraft the water heater or a furnace or mess with your wood stove or your fireplace, whatever. Oh, this is a bigger problem. This is something we should have anticipated and should have asked questions about. This one is gonna move the house way far towards the cliff. And to me, that’s the simple part is making sure you ask the question, where I feel bad is while building science can tell you what things might happen, they can’t tell you always to the degree of what will happen or how bad it will be or what that consequence might be. And to me, that’s the whole point of testing. So now you say, “Aha, I got an idea here, but I don’t know exactly how far towards a cliff it’s gonna move me. So what I need to do is test now and test later to see if there were any unintended consequences or reactions to my one thing I did to the system that might be problematic or need to be addressed.”

PH: And so I’ll kinda close with that but I think it’s really important. And you can’t just by a phone call or on a piece of paper, just guess what those reactions or consequences might be into what degree, they will occur.

BO: Thank you, Pat, so much, this is amazing information and I hope everybody who owns a house will sit down and commit an hour and hear the words that you’re saying. You are preserving their investment in their home by giving it more durability. Go ahead, Tess, sorry.

TM: I was gonna just end this with one question to Pat. Pat, would you buy a storey-and-a-half house to live in yourself?


PH: I thought you were gonna ask about that. That’s a long answer, but I’ll just say this. I love story-and-a-half houses. They were a built with a very intentional purpose. They’re incredibly material efficient. They had a lot of flexibility built into them, especially when we built them here with basements. Another whole question or serious things could come around that.

TM: We’ll talk about basements the next time.

PH: Yeah. But the point is, it was a marvelous design for the times. I think it even still has application today but we certainly wanna maintain the ones that we have. However, they were built in a time when energy was cheap, where people ran their indoor humidity, at 15-20% in the winter, and that was it, and the snow melted off the roof and ran down and was gone. We didn’t have the ice dams as much there and it worked actually from a lot of perspectives, but it wasn’t efficient. Maybe not durable either because there still were ice dam issues and condensation issues on occasion. But we came in and tried to bring them up to a new standard during energy crisis, and what we started to learn in the ’80s and ’90s. And that really is what pushed them over the edge, pushed them over the cliff.

PH: So it’s just a matter of coming back. And if you take the principles again, of sequence and I should mention that sequence again ’cause I think I misspoke one time. But take care of combustion safety then ventilation, then water control, then air tightness, and then insulation. If you follow the sequence, you can do this safely. Then the second piece is, think about the control layers and when you get done, that roof has to have the four control layers, water control which is the roof, primarily, and then it has to have thermal insulation and air barrier, vapor protection, and it has to have, remember, the cladding system that can drain and dry. So it has to be a ventilated roof system that will provide that relief or drainage and dryness should there ever be a moisture problem in the assembly. Can we do that on the story-and-a-half? Absolutely.

BO: I think you’ve got a paper that tells you exactly how to do it, right?

PH: We do. Yeah, we call it project overcoat. It is slick, really ends up being a hybrid, not a pure perfect roof, but it works. Yeah, it’s not for the faint of heart, it’s not for the person who looks for the cheapest bid, but it absolutely works. It brings that story-and-a-half house from the ’50s through all the oopses and misery and puts it in the next century.

BO: Awesome. See, my favorite house lives on forever. Thank you, Pat, thank you for saving story-and-a-half houses and urban centers all across this country. We really appreciate that stuff.

PH: I would buy one, but I’d picked the right one that hasn’t been messed up yet, and that I can actually implement the overcoat on.

BO: Alright, thank you, Pat. I’ve gotta put a wrap on this. You’ve been listening to Structure Talk, a Structure Tech presentation. We will catch you next time. Thanks for listening.