Below is the text version of the Building America webinar, "Stump the Building Science Chump — Joe Lstiburek." Watch the webinar.
Linh Truong:
... with the National Renewable Energy Laboratory and I'd like to welcome you to today's webinar hosted by the Building America program. We are excited to have Lena Burkett and Joe Lstiburek with us today.
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Before our speakers begin I'll provide a short overview of the Building America program. For more than 20 years the U.S. Department of Energy Building America program has been partnering with industry to bring cutting-edge innovations and resources to market. Our moderator today is Lena Burkett, a fellow with the U.S. Department of Energy Building Technologies Office. I'd like to welcome Lena to start today's presentation and introduce our very first building science chump.
Lena Burkett:
Hi and welcome to the first ever Stump the Building Science Chump. I'm Lena Burkett with the Department of Energy and we are delighted to have Joe Lstiburek with us today. I think just about everyone in the field of building science knows about Joe but for those who don't Dr. Joseph Lstiburek is the founding principal of Building Science Corporation. He holds a bachelor's of applied science in mechanical engineering, a master's in engineering and civil engineering and a doctor of philosophy in building science.
During his master's degree he developed the air drywall approach to air barriers. Joe is also an acclaimed educator who has taught thousands of professionals over the past three decades and has written countless papers as well as the bestselling builder guide. Joe founded BSC in 1990. Anything else you would like to add, Joe?
Joe Lstiburek:
I'm not a Broncos fan.
Lena Burkett:
All right. So we have asked folks to send in their best building science questions for Joe and we've received some great ones. If you have any questions that come up through this session you're welcome to type them into your questions pane and we will try to answer them right here today if we can work them in timewise.
So before we get onto some of the more technical questions I want to ask a bit about your career. Was there a defining moment when you realized that building science would be the focus of your career?
Joe Lstiburek:
When I couldn't get a job in my chosen profession, which was aerospace engineering, being out of work and construction were the only people hiring I fell in love with construction. So the best thing that ever happened to my career was not being able to get a job.
Lena Burkett:
Well, what did you initially want to do in aerospace engineering?
Joe Lstiburek:
Well, my father was an aeronautical engineer. I was trained as a classic rocket scientist. When people say, "It's not rocket science," I can actually argue the point.
Lena Burkett:
Well, that's great. Well, I've got a related question for those kind of just starting out in this field can you share like one of the most valuable experiences early on in your career was and how it shaped your work?
Joe Lstiburek:
Well, I was adopted by a bunch of old guys who mentored me. I was one of those lucky people that found people who were much smarter than me and I listened to them. I was mentored by two and three of the giants in the profession. And at the time I was young and stupid, didn't realize how lucky that outcome was. And so the most important thing I could advise people starting out is find people that are smarter than you and listen to them.
Lena Burkett:
Great. That's good advice for anybody. OK, we'll get into one of the more technical questions. One of the emailers wrote: "BSC has great articles about insulating old masonry buildings in cold climates, mostly addressing the freeze and thaw cycle. The question is what are good practices to insulate historic masonry buildings in hot, humid, and very rainy climates like New Orleans?" The emailer has two issues on her mind to tackle the: the historic preservationists' ruling out of spray foam directly on the masonry, and masonry staying wet almost all year round from frequent rain where it can't dry to the inside, growing unsightly algae and owner complaints.
Joe Lstiburek:
This is a controversial subject. I actually wrote about it a couple of weeks ago in Building Science Insight 95, which is titled, "How Buildings Age." There are a whole series of details at the very end of that Building Science Insight that graphically show how to insulate on the inside of masonry buildings without necessarily using spray foam.
If you're building in climate zones 1, 2 and 3 exterior drive from the inside to the outside is really not an issue. So requiring a high degree of air-tightness of your interior lining, or vapor control on the interior lining is unnecessary. What you want to do is allow the assembly to be able to dry to the interior as well as to the exterior.
So let's assume that rain wetting of the building façade has been tackled — and I'm going to address that in a second. What we want to do is increase the air-tightness of the wall, and one of the easiest ways to do that is to paint the interior of the wall with a fluid-applied, vapor-permeable water and air control layer, typically the stuff that we do on the outside of commercial buildings for air barrier systems that are vapor permeable, can be applied to the inside of that masonry wall. And then if you don't like spray foam, which apparently some people don't, then it's one of the systems we like to use would be rigid mineral wool. Rockwool works really, really well, held in place with furring strips or a hat channel and anchors.
Believe it or not, also studding out the wall to the inside with a wood frame and insulating it with damp spray cellulose or netted cellulose also works. And the key is to not have an interior vapor barrier to the interior of that assembly.
Now all of this is predicated that the exterior façade is not being wetted in a concentrated manner from a rainfall perspective. And that means providing drips and flashings and protection against that saturation.
In terms of the algae growth on the exterior one of the historically successful methods in dealing with that after interceding with respect to rain wetting and saturation with flashings and drips is lime-based coatings. Lime is a fabulous inhibitor for algae and lime washes have been used for hundreds of years to control algae growth. And so bottom line, fluid-applied air control layer on the inside; any insulation system you pretty much want to the interior of that, drips and drip edges on the exterior coupled with a lime wash and you're good to go.
Now in terms of the historic preservation it's really not spray foam; they haven't ruled out spray foam, they've ruled out techniques that cannot be reversible. If you were to apply on the masonry a coating that allows you to provide a bond break between the spray foam and the interior lining or the masonry you could use spray foam if you wanted to do that.
Lena Burkett:
And what kind of coating would you suggest for that?
Joe Lstiburek:
Well, to me I would have used — I would use one of those fluid-applied exterior vapor barrier coatings. So you could spray the foam directly on it. I mean I think it's a good idea in general is before you apply any of the insulation systems you apply that layer to control water seepage, air leakage, provides a bit of a vapor throttle to the interior, and also provides a bond break if you actually wanted to use high density or low density spray foam.
Having said that there's nothing wrong with using cellulose or fiberglass or mineral wool, and again, those details can be found at the end of Building Science Insight 95.
Lena Burkett:
Great. Lots of good options there.
We've got another one from the same emailer who asks: "What's the research basis for 5 ACH50 as the threshold of mechanical ventilation requirement? Florida and Louisiana amended their statewide codes to 3 ACH50, partially based on great fear of causing mold in the HVAC system and high relative humidity and anecdotal claims that houses in hot, humid climates with ACH between 3 and 5 have no apparent IAQ problems, plus ventilation systems tend to get turned off, cause discomfort, or fail. Of course there's no — there's also resistance to cost of adding equipment not needed before. So, what is out there to disprove and overcome those assertions and objections in the hot, humid climate?"
Joe Lstiburek:
Sure, another easy question. This one is based on some history, politics, almost no health science but a lot of passion. And so bear with me with the history. The 5 ACH and the 3 ACH50 are practical air-tightness levels that wood frame builders were able to achieve in the late 1980s and early 1990s in terms of energy conservation features. The trend was towards "build tight, ventilate right," and these were targets for tightness in terms of what would provide for a good energy efficient building in a cold climate.
In 1982 Canada had something called the R2000 program and the air-tightness number was 1.5 air changes at 50 pascals, and that was a guess. I picked that number as a number halfway between 1 and 2, as one bunch of activists was pushing for one; the other bunch of activists were pushing for two. I split the difference at 1.5, and also felt that it was half of the Swedish practice which was three air changes per hour. And I figured Canadians were better hockey players than Swedes, so 1.5, twice as good as the Swedish 3, and that's where we went.
Lena Burkett:
Yeah, that's good logic based on the hockey.
Joe Lstiburek:
Well, actually it turned out to be actually incorrect. When we ended up building those houses it became a boutique program and it was not really achievable. And so when I started working in the United States we built about 1,000 houses with several builders in Chicago, and they were dealing with freezing pipes and comfort complaints in the early 1990s. By getting rid of the big holes it was easy for us to get below three air changes per hour at 50 pascals.
And so with three air changes per hour 50 pascals was based on over 1,000 houses built over a two-year period in 1994-1995, by getting rid of the big holes at bathtubs, stairwells and whatever. And at that point we were getting higher levels of moisture; we were getting basically condensation on double-glazed window systems. And we knew from our experience in Canada with the R2000 program that we needed some ventilation. And so we picked 10 CFM per person.
So in the mid-1990s 3 ACH50 was based on cold climate houses with basements, getting rid of the big holes, and we control the moisture condensation on the windows for 10 CFM per person because that was sort of the experience coming out of the early 1980s out of Canada's R2000 program.
Well, the reason that basements were invented was we were able to put our mechanical systems in them. There was no way that a slab on grade house, single-storied, with a vented attic with ductwork in the attic could get to three air changes per hour at 50 pascals using standard production building techniques. And we found that five was a reasonable number to pick.
So the three came out of basement houses with no ductwork-embedded attics; the five came out of slab on grade houses with ductwork in vented attics. And there was no requirement for controlling condensation issues in hot, humid climates. And so the question was are we worried about any other contaminants and we simply added the 10 CFM per person number as a general guideline for the country.
So the three came out of how tight could you get without doing craziness with basement houses; the five came out of how tight can you get without doing crazy stuff with ductwork in vented attics. They were basically practically based numbers.
In terms of the 10 CFM per person that came out of controlling condensation on double-glazed windows in cold climates. There is no health basis for any ventilation rate at this point. It's been a giant, political guess. The current building code calls for 0.01 CFM per square foot plus 7.5 CFM per person as a ventilation number, and what that number — and it makes no distinction between cold climates and hot climates. Applying that number to a house built to the 2015 IECC will lead to a part-load humidity problem if you are less than I guess I would say 2,000 square feet. So that's going to require supplemental dehumidification. And certainly that's the case if you're dealing with townhouses and row houses.
So let me sort of summarize: the three came out of how tight could you get reasonably without doing craziness with a basement house with a mechanical system in it. The five was how tight could you get reasonable with slab on grade house with the ductwork-embedded attic. The ventilation rate was based on controlling condensation in cold climates. There is no basis at this point from a health perspective for any of the numbers in ASHRAE standard 62.2, and there's a big argument about what that number ought to be.
I won't get into that argument except to say that I am right and they are wrong but that's — what else would you expect me to say?
Bottom line: Any number between 10 and 20 CFM is going to require some type of part-load humidity control in climate zones 1, 2 and 3 east of the Interstate 35 in Texas and south of the Mason-Dixon line.
Lena Burkett:
OK. Great. So I'm going to take one of the questions that's coming in from the audience, which I anticipate your answer will be, "It depends," but I will let you elaborate.
The question is: "Are heat pump water heaters a good choice in cold climates?"
Joe Lstiburek:
Yes, it depends. It depends on what fuel choice you have available. If you have natural gas I prefer natural gas sealed combustion water heaters. If gas isn't available a heat pump water heater is an excellent choice.
Lena Burkett:
OK, great. So stepping away from the more technical questions, more about being an expert in the field: if you could magically instill one piece of knowledge in to the heads of all building _____ professionals what would it be?
Joe Lstiburek:
Turn off the computer. Don't —
Lena Burkett:
OK, you're referring to modeling?
Joe Lstiburek:
Oh, yeah. That's insane. I mean hydrothermal analysis is out of control. My favorite scene in "Star Wars" was, "Luke, turn off the guidance system. Go with the force." People are believing in the simulation world as opposed to the real-world experience. And if you need to run a hydrothermal model to determine whether or not your wall or roof assembly works you've got the wrong design in the first place.
And so, you know, this modeling craze is leading to bad engineers, bad architects, bad policy. So — anyway, enough said.
Lena Burkett:
Right. And another maybe a little bit more personal question: what is the next high-performance improvement you plan to make on your own house?
Joe Lstiburek:
[Laughs] Well, I need to repair the bad judgment I made in the past. When Betsy and I — Betsy's my long-suffering wife and partner. When we renovated our 1850 farmhouse and insulated it from the exterior I only used two inches of continuous insulation and have been embarrassed ever since. I should have added six instead of the two.
And so 20 years ago that led to a super-insulated wall and today it's, "Really? R20? Joe, come on. You should have done better." And so I'd love to be able to redo the cladding and insulation system and upgrade the windows from basically double-glassed gas-filled to a triple-glazed, krypton-filled, a nice R5 or R6 window. So those are the glazing and the walls, we've already done the roof and the foundation systems twice.
It's the classic researcher-engineer-builder married to an architect: we never stop renovating our house.
Lena Burkett:
Right. OK, we've got a pretty complex one here from one of the emailers. She writes: "Regarding excessive humidity buildup in an attic and/or living space of homes with walls and attics encapsulated with open-cell, low-density spray foam in climate zone 3 —" I'll let you read some of the details about that, but she starts out her four-part question with: "If supply air is added to an unvented attic encapsulated with open-cell low-density spray foam to try to reduce excessive humidity buildup in the attic is this a primary solution and does an extra return pathway to the living space need to be added?"
Joe Lstiburek:
Let me sort of step back and say here's the politics of all of this, and the physics. We need to remove moisture from that attic, and that moisture is typically removed in a house by the air conditioning system. So in essence going to be dehumidifying the attic the same way we dehumidify rooms in the house: we supply air-conditioned air to a bedroom; we supply air-conditioned air to the attic. That air-conditioned air that is supplied to the bedroom in the attic has to find its way back to the return side of the system. So we need some kind of return pathway.
Now the amount of air that we need to supply to air condition the attic is so small, around 50 CFM for every 1,000 square feet of ceiling area, the normal leakage of the ceiling is able to provide that return path. But what's also nice about this is that to me as an engineer the logical way to do this was to have a supply and a return. But the building code, the fire folks would have a meltdown because the spray foam needs to be covered with a thermal barrier. And even with the thermal barrier people are not happy about having a return path.
And the hypocrisy and the irony is quite stunning. When we had leaky ductwork that were leaking 150 and 200 CFM into these attics that were constructed with open-cell spray foam there wasn't a problem. So when we built tight ductwork and got rid of the 150 to 200 CFM of leaky ductwork and reduced it to almost nothing, and then add a 50 CFM supply in a controlled manner that violates their fire code. And so crappy workmanship was acceptable, but a design flow at a significantly lower rate was unacceptable. It boggles the mind.
And so if you didn't have to have a code official involved I'd put a return duct in with a supply. So that's my preference, a supply and a return, balanced. If the code people are involved then you put in a supply duct with no active return and rely on the leakage or poor workmanship at the ceiling to attic interface.
Can you avoid all of this with the dehumidifier? The answer is yes, of course, but it's a rather expensive way to deal with a very small amount of moisture. Could you deal with it by putting in an exhaust fan that simply pulls air out of the attic and dumps it to the outside and basically pull air from the house, ventilate the house, in essence, through the attic? The answer is yes, of course you can do that. We do that the same way with crawl spaces; it's not unusual to condition crawl spaces to put an exhaust fan in the crawl space and pull air out of the crawl space, have the air — intake air taken from the house and so you're providing exhaust ventilation of the house through the crawl space. So all of those are possible.
Now if you have high density foam this is not necessary because the moisture issue that's happening is the storage of moisture in the plywood or OSB roof sheeting. The closed-cell foam, basically the moisture storage of the wood framing from the air; the open-cell foam doesn't. You could also coat the open-cell foam with a vapor retarder coating and avoid the issue as well.
Lena Burkett:
Great. OK. She also asks, because she's concerned about the relative humidity in the living space itself, are these techniques just to address the excessive humidity in the attic itself or does that humidity ultimately move into the living space and cause problems there?
Joe Lstiburek:
Well, I understand that the humidity in the attic came from the living space. So in other words the attic isn't creating the moisture problem in the house, the house is creating the moisture problem in the attic. And so the air conditioning system in the house is more than adequate to dehumidify that part of the house, the house itself. What we're doing is simply coupling the attic to the air conditioning system of the house. So it's already doing its job in the living space; what we want the air conditioning system to do is to also help the small amount of moisture in the attic.
Lena Burkett:
Great. And I think that you've pretty well answered the remaining two questions as well, so I'm going to move on.
This one, we'll see if it might stump you. It says, "Energy improvements in dozens of homes with potential asbestos-containing material such as vermiculite get deferred due to cost of mitigation when only two percent actually have asbestos. Vermont is experimenting with a process to air seal while leaving the vermiculite in the attic, but still no blower door can be used to determine air sealing was sufficient.
Is there an affordable strategy to address the problems with asbestos, vermiculite and no insulation?
Joe Lstiburek:
I think managing the vermiculite in place is absolutely the correct strategy and I think the Vermont approach is correct. And I don't believe a blower door test is necessary to achieve, to verify air-tightness. I think that is pretty simple to, with an infrared camera and visual inspection to figure out where the sealing needs to be done. And instead of pressurizing to 50 pascals just measuring a small pressure differential between the house and the attic is good enough to be able to tell how effective you are. So you could do it with a manometer and a very small fan and visual inspection and you're good to go.
Lena Burkett:
Great. Yeah, that makes a lot of sense to keep it undisturbed and that there actually are some tests that can be performed without the disruption of a full blower door test.
OK, this one I'm not sure is one that all of the builders and building scientists out there will relate to it, but we'll give it a go. This emailer asks: "Dear Dr. Chump, in climate zone 5 on clear sky evenings in shoulder seasons (i.e. spring and fall when it's nice and sunny and pleasant during the day but frosty at night) is there any aesthetically pleasing way to prevent condensation on the interior of flat walk-on skylights located in the roof of a natatorium where the dew point temp is maintained (on paper) at 65° F?
Joe Lstiburek:
This is an easy answer: you add an extra layer of glass or extra layer of plastic, a thin polyethylene sheet basically to create a triple-glazed layer. Think of it as an interior air-tight storm. We do this all the time.
Lena Burkett:
OK. Great. I'm going to ask some of the questions that have come in during the webinar. Let's see, OK, one of them is what is the best ventilation strategy to use in a cold climate, Connecticut or Massachusetts, to use in a home with 3 ACH50, an HRV or an ERV? And how do you convince builders to use this more expensive option, HRV or ERV, rather than a Bass fan on a timer?
Joe Lstiburek:
Exhaust-only ventilation is ineffective. The best approach is balanced ventilation. And balanced ventilation at a lower air change rate is recommended — balanced ventilation at a lower air change rate than is recommended by ASHRAE standards [audio static] is my preferred option. So you size the system according to 62.2 but ventilate at half that rate. If you do that then HRV is the recommended approach.
An ERV is necessary only in a cold climate when the ventilation rate is too high and you end up with excessive dryness. You end up with overventilation to such an extent that the house becomes uncomfortably dry and you have to add a humidifier. Well, that's insane. And so if you want to ventilate at a high rate without having excessive dryness then an ERV is recommended.
So if you ventilate at a reasonable rate, which would be half of the 62.2 number with balanced ventilation an HRV is recommended. If you're going to ventilate at a high rate in order to avoid wanting to put in a humidifier, which is a really bad indoor air quality idea, you would go with an ERV.
Lena Burkett:
OK. Great. We've got one question that came in during the webinar that's actually in relation to the first question that you answered about masonry buildings. It says, on the very first question Joe mentioned that wet historic masonry buildings need to breathe both to the interior and the exterior. But then he said about adding a vapor barrier as a bond break between brick and sprayed insulation. Wouldn't a vapor barrier contradict what he said earlier about the two-way breathability with the exterior masonry wall or is that a matter of degree of the vapor permeability?
Joe Lstiburek:
I never used the word vapor barrier; I used a fluid-applied air control layer, and that could have some throttling effect on the inward drive. So it's not unusual to have these systems that between 10 and 20 perms. I'd pick something around 10 perms and you're good to go. So you want to slow down the drying of the wall to the interior so that as it passes through this layer and it gets into the insulation lining, the inner lining, that it's at a slow enough rate that it can get out of that to the interior more rapidly than it can get in. So we want a small throttling effect.
We also don't want a vapor barrier on the exterior, and the reason for that is is that when it gets hot and the sun beats down on the masonry the temperature of the masonry is higher than the outside air and you actually get drying to the exterior as well. So if you were to pain the outside with a low permeance paint with bubble and blister — it was basically the paint telling you that you did something dumb: you put a vapor barrier on the outside.
So what we want, something that breathes on the outside but reduces water absorption, something that breathes to the inside but not too much. So maybe Goldilocks: Not too hot, not too cold, just right. Not to vapor open, not to vapor closed — just right. Ten perms has been what seems to be working historically in the projects we've been dealing with over the last 20 years.
Lena Burkett:
Thanks for that clarification.
OK, speaking of vapor retarders and the like, another question from our emailers is: "The never-ending debate between climate zones — to add a class I or II vapor retarder to the interior of the wall or not to? It's my understanding that in colder climates when a wall simply has greater than R7.5 continuous rigid insulation on the exterior a class III vapor retarder can be used on the interior of the assembly. Other envelope critics claim that a class I or II vapor retarder such as polyethylene plastic should still be installed on the interior prior to drywall. For cold climates this would mean that the wall simply is sandwiched between non-permeable layers which don't allow the wall to dry. Since the dew point changes depending on the season what is the best vapor retarder approach for cold climate wall assembles?
Joe Lstiburek:
Well, this argument has been happening since I got my first engineering degree. The short answer is that if you put enough continuous insulation on the outside of your assembly to elevate the temperature of what we would call the condensing surface, which was really the backside of the sheeting an interior vapor retarder is not required. So if you have enough insulation on the outside of keep the wall cavity warm enough an interior vapor throttle is unnecessary. If you don't put enough insulation on the outside an interior vapor throttle is necessary.
Now the problem with an interior vapor throttle only occurs when we have high levels of air conditioning. So let's say that we're in Montreal. There are only two seasons in Montreal: this winter and last winter. They don't air condition there. They play hockey — in July. It's horrible. It's cold. A plastic vapor barrier on the inside of a building in Montreal is perfectly acceptable.
You go to Chicago — I lived in Chicago. Chicago has summer. Chicago has humid summers. Chicago has humid summers and they condition their buildings. Putting a plastic vapor barrier on the inside of a wall in Chicago is a really dumb idea for the air conditioning period. But Chicago also has a winter. So if I'm going to have plywood or OSB on the outside of a 2x6 wall in Chicago I would probably want some kind of a throttle on the inside, and so that's where we would use historically craft-based insulation or a vapor retarder coating of around — that would give us about one perm as opposed to 6 mil poly.
I wouldn't need to do any of that if I put enough continuous insulation on the outside to warm up that plywood or OSB, and in Chicago that would be R7.5. The amount of insulation I put on the outside as compared to the inside depends on how cold it is outside and what I have happening on the inside of my building.
If I was going to build a humidified pressurized hospital or museum or art gallery in Minnesota I would have all of my insulation on the outside of my cavity and have no cavity insulation at all. Now I'm in Minnesota; they don't have the same air conditioning load demand in Chicago. It's perfectly acceptable to have 6 mil poly on the inside of a wall in Minneapolis, 2x6 wall, OSD on the outside, building paper, a cladding system. That wall is able to dry to the outside, and in the summertime the poly doesn't get wet enough from the inward drive to cause a problem.
Now what if I'm not happy with just R20 insulation in Minnesota and I want to add continuous insulation on the outside and I add another R5 or R 10? Most of the continuous insulation is the vapor barrier. And so yes, we end up with a double vapor barrier.
If your windows don't leak and you've done good rainwater management a double vapor barrier will work. It has worked historically. Now it's not my best solution. What I would do in Minnesota if I had a plastic vapor barrier on the inside I'd go to mineral wool. I'd go to Rockwool or I'd go to rigid fiberglass on the outside and thereby I would not have an exterior vapor barrier with my continuous insulation. So bottom line: you want to avoid plastic vapor barriers which are class one in anyplace that has a lot of air conditioning.
You can get away with it in cold climates if you allow the wall to dry to the outside. It's riskier with a continuous insulation on the outside but we've gotten away with it because we've done excellent detailing at the punched opening such as windows and doors and the like.
Let's not ask that question again, shall we? Let's just avoid it.
Lena Burkett:
OK. All right, one more that came in as we were speaking. It asks: "When you insulate a wall with fiberglass insulation you need to caulk all the stud bays. Does it help to do the same when you insulate the attic floor?" And I have a secondary question to that, which is that: "Typical building science practices tell us that this is necessary to have an air barrier on all six sides of an insulated wall cavity but some building scientists no longer consider that necessary." So what are your thoughts on both of those issues?
Joe Lstiburek:
Well, I don't think you need to caulk all of the studs. And I think one really good air barrier on the outside of your framing is sufficient with most cavity insulation. So this idea of having to have a double air barrier on both the inside and the outside I think is unnecessary. I think historically we've gone from taking the air barrier from the inside and to take it to the outside. Back in the old days we would wrap it with a plastic film on the inside. That was insanely difficult to do. Then we started using interior gypsum board with draft stopping as the air barrier, which is pretty reasonable to do but doesn't give you as high performance as putting it on the outside and having the sheathing become the air barrier.
So I like it on the outside. That's where it's easiest to make continuous. Commercial construction, that's the place where we've decided it goes. I think residentially that's the evolution is going to go from the interior side of the framing to the exterior. And we don't get very much convection and movement in the cavity insulations, especially since we're now adding continuous insulation to the exterior.
So a longwinded way of saying if you have it on the outside at your sheathing, and you have a layer of continuous insulation over that to reduce the temperature difference across the framing on the inside, an additional air barrier on the interior is unnecessary with fiberglass or cellulose insulation.
Lena Burkett:
All right. Great. So you mentioned some of the kind of evolution of residential building practices and some of them maybe tending towards practices that we see in the commercial area. So kind of along those lines, or other types of evolution in the industry during your career what do you think has been the greatest change to the building industry?
Joe Lstiburek:
Water management. What's ended up happening is that when we built out of thousand-year-old trees and rocks without insulation we didn't have to be very good at keeping rainwater out of a building. Rain would wet the building and so what if a rock got wet? So what if the thousand-year-old part of a tree got wet? It's a lot of energy flow; the walls were able to try in both directions.
But when we started going to frame systems, engineered wood — I view engineered wood is an insult to wood engineers, by the way. We went to OSB, which is the spam of wood. It's insane. These products can't get wet, and we insulate the walls heavily; there's very little energy available to evaporate. So we ended up having to change the way we installed every window and door. We went to pan flashings. We ended up discovering that we had to do exceptional water management of balconies and decks, or rooves and walls. So we went from not really having to care much about rainwater management to having to be fastidiously anal about it. That's been the biggest change.
Lena Burkett:
OK. Got some more coming in through the question pane. One of the audience members writes: "What about the newly-available sheathings that have an integral attached half-inch rigid insulation which is nailed up with the insulation between the studs —" stud faces, I think he means — oh, "between the stud space and the inside face of a sheathing the sheathing that it's a part of." Is this type of rigid wrap in zone 4 OK or is this new product type a problem waiting to be discovered at the sheathing product and condensation??
Joe Lstiburek:
Well, if the amount of insulation on the inside of the structural sheathing is enough condensation will be controlled. And if I've got one inch of rigid insulation adhered to the back side of some OSB in climate zone 4 that's really not going to be an issue. But I'm going to need much more than that in climate zone 6, for example.
The code has a very nice table that tells you what amount of thermal resistance you need in that insulation to control condensation. And so the colder the climate the greater the amount of thermal resistance you need on that insulation layer that's bonded to the inside of the OSB.
Lena Burkett:
All right. I'm going to step away from condensation for just a bit; see if this one might stump you. An email wrote: "I installed cedar shingles on my addition to my earth-bermed passive solar house. The red squirrels are eating the shingles. Do you know what I can do to stop them from eating these shingles?"
Joe Lstiburek:
Get a squirrel gun.
Lena Burkett:
OK. Anything else a little less violent?
Joe Lstiburek:
Well, now, let's be serious about this. I mean the squirrels want the shingles for a reason. It's some kind of a food source to them. And so why not coat the shingles with something that repels them? You can use a highly-alkaline coating system to basically protect the wood and basically chase the squirrels away. They're not going to want to eat it because it's no longer tasty for them. So change the food source without changing the color too much by coating it with basically a squirrel repellant that also provides UV protection.
Lena Burkett:
That's great advice.
OK, one more has come in through the question pane. "What is your favorite way to air seal and insulate a floor above an unconditioned area such as a garage or a porch?"
Joe Lstiburek:
My favorite approach is to put a continuous layer of rigid insulation under the framing and seal the joints. So if we're talking residential construction I would love to take an inch and a half of foil-faced isocyanurate and tape the joints. And that would be my air-sealing approach as well as my continuous insulation. And then I would cover that with 5/8-inch Type X gypsum board for the fire protection because I'm assuming this is — you've got a garage under there or an exposed balcony or something else. That's my preferred approach.
I think I wrote about it in one of the Building Science Insights where I think I called, you know, Bobby Darin does floor systems. He had this wonderful song: "Splish, splash, taking a bath." It'll make sense if you find it on the website. Bobby Darin was a — never mind — before Elvis, yeah. I know.
Lena Burkett:
All right, great. So speaking of sinking back into the depths of history with Bobby Darin, looking back on your career you have given a lot of great advice and written a lot of really important guides. What do you think was the worst advice you're given or the biggest building science mistake made?
Joe Lstiburek:
Wow.
Lena Burkett:
No pressure.
Joe Lstiburek:
No, no, no. We did a lot of dumb things with plastic in the wrong places back in the early days. My mistake was thinking that the prevention of wetting was more important than the encouragement of drying. And so a lot of this stuff in the early days of my career was on preventing things from getting wet, and those techniques basically allowed things to stay wetter longer after they inevitably got wet.
So I got the focus wrong: you should always encourage drying over and instead of the prevention of wetting. Because many of the techniques for the prevention of wetting also inhibit drying. And I didn't get that figured out early enough in my early days. So it's OK for something to get wet as long as it can dry. And drying is more important than wetting. Fundamental, obvious now, but it would have been nice to have known it 30 years ago.
Lena Burkett:
OK, one more coming from the audience: "When performing a blower door test and finding air leakage at exterior wall electrical outlets what part of the wall assembly is the air coming from?
Joe Lstiburek:
It can come from all kinds of places. It can be coming from the top, it can be coming from the bottom, coming from the sides, it can be coming from the outside or the inside. Most of the time it's coming from the top of the wall at the top plate. But that's not always the case.
Lena Burkett:
OK. Yeah, it can be coming from a lot of different areas.
Joe Lstiburek:
There are actually 12 flow paths that are possible, as bizarre as that seems. But more than half of the time, based on the gray hair that I have, it comes down from the top.
Lena Burkett:
OK, great. So another one, thinking about your career and your experiences, who would you say, besides yourself or anyone else who works at Building Science Corp. who is your favorite building scientist?
Joe Lstiburek:
I love listening to John Straub, Professor Straub, "Strauby." He's got an insanely wicked sense of humor. He's the best punster in the world. I don't get to see him as much as I'd like to because usually we're at the same conference at the same time. And that's very irritating because I can't get to see him because I'm speaking.
Lena Burkett:
All right. I think we've got time for one more. This one just came in from the audience and it says: "In general what's your opinion on the zip sheathing system with and without internal insulation?"
Joe Lstiburek:
I like zip sheathing. The trend towards combining the water and air control layer in a sheathing is what we've been seeing commercially. So we went from interior air control layers to exterior control layers; the exterior control layers were basically some kind of a membrane or a film or a building paper on the sheathing. On the commercial side we went to fluid applieds, and then it took time to get the materials spray-applied and the fluid applied on the sheathing. So then commercial folks figured out well let's have the sheathing come with the coating already attached and deal with the joints. And one of the manifestations of that is the zip sheathing. So I think that's the winning technology trend that we see commercially and I think that's what we're going to see residentially as well.
Lena Burkett:
All right. OK, I think we probably have time for one or two more then. That was a quick one. So one question that just came in is is there any reason to go to the trouble to try to cover the underside of floor insulation to stop air washing in a crawl space?"
Joe Lstiburek:
Yes. And more importantly it's more important to prevent moisture from — ventilation from getting into that space. So what we need is some kind of a sheathing on the underside of the floor framing that provides air-tightness and vapor tightness. And so absolutely.
Lena Burkett:
And how would that compare to just converting that crawlspace to a unvented crawlspace?
Joe Lstiburek:
Well, I hate the term "unvented" — I prefer the word "conditioned." But a conditioned crawlspace will significantly outperform a vented crawlspace. But it's more difficult to do. And there are site limitations: conditioned crawlspaces probably are a bad idea if you're in the middle of a sandbar in the Gulf of Mexico. That would be the entire State of Florida. So where you have flooding you probably don't want conditioned crawlspaces. So conditioned crawlspaces in the Carolinas would be a great idea; conditioned crawlspaces in Washington State would be a great idea. Vented crawlspaces in areas where we have lots of water are preferred.
Lena Burkett:
All right. And I see that someone is following up on my favorite building scientist question and I'm going to throw this out there just as a fun last one: who is your favorite hockey great?
Joe Lstiburek:
Oh, it's not even close: Bobby Orr. Bobby Orr had his career cut short because of a knee injury.
Now in terms of the greatest nice guy hockey player of all time: Bobby Hull. Bobby Hull had a son who was also a great hockey player, Dennis Hull. And I was introducing my son and my daughter, who were seven and eight years old, I met him at an airport and that was — I walked up to him and I said, "Mr. Hull, can I introduce my son and my daughter to you?" He laughed and he said, "Yes, bring one over." So I brought my son Andrew, who's eight years old, up to him and he leaned over and he said, "I'm Dennis Hull's father." I just started crying. What a good guy.
Lena Burkett:
That's a great father. So both in the story, great fathers.
All right, well we're just about out of time. Thank you, Joe. This has been a lot of fun, and I think that we have all learned a lot. So today Joe covered a lot of topics. If you'd like to find out additional resources related to these topics or other building science topics you can visit the Building Science Solution Center. The Solution Center provides expert building science information for building professionals looking to gain a competitive advantage by delivering high performance homes.
You can also register for free to customize the content and create field kits, create point-of-sale fact sheets and training materials and access your saved and created content from your mobile device. Linh, back to you.
Linh Truong:
All right, thanks, Lena. And just as Lena said, thanks, Joe, for your time and expertise today. Aside from the Broncos comment we do appreciate all the advice that you've given out today.
We'd also like to remind the participants today that you can find additional resources on the Building America website at the URL that you see on that slide. And on the next slide you also will be able to see that we do have a monthly newsletter and so we encourage you to sign up for that so that you can learn about upcoming webinars by future Stump the Building Science Chump and other resources as they become available.
With that I just wanted to thank everyone today. You guys have been a wonderful audience. Thank you for all the questions that have come in. There's definitely no way that we could have answered all of them today. So you were a great audience and thanks for your time. Thanks, Joe. Thanks, Lena. And with that I just want to remind you that we will be posting the webinar today on the Building America website.
With that have a great holiday everyone and thanks for your time.
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