Insulation Retrofits on Old Masonry Buildings - Building Science Podcast
This week, Dr. Joe Lstiburek talks about retrofitting old masonry buildings with insulation and the water problems that it can cause.
This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube, of Building Science Corporation.
For information on attending a live class, go to BuildingScienceSeminars.com
Last week Dr. Joe talked about brick walls and water problems. This week, Dr. Joe talks about retrofitting old masonry buildings with insulation and the water problems that it can cause.
How Do You Retrofit an Old Building to be Energy Efficient And Durable?
The context here is very important. You don’t insulate the wall of a mass assembly until you’ve taken all of the other low-hanging fruit into account, right?
What’s the biggest penalty in a big stone house? Well, the glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. system — followed by what? The roof, followed by… Air tightness, right? Then the efficiency of all of the other stuff.
This stone wall is already an R-10 wall. The low-hanging fruit is not the wall; I already have an R-10 wall with an R-1 window. So I’m not going to deal with the wall until I’ve done the other things.
Historic restrictions may get in the way
Now sometimes I might not be allowed to do some of the other things. You know it’s very difficult sometimes to redo these windows because of the historic restrictions. There are ridiculous rules and these agencies are going to end up having to start recognizing that, look, we've got a planet to save and a republic to protect. Now there are all kinds of folks that have different views. There’s a pretty famous architect in town, who interprets the historic tax credit stuff differently than other people, and we should be able to rehabilitate and do something with these windows. But many times you’re going to be told that you can’t touch the windows, and if you can’t touch the windows, you’re going to run out of things to do pretty quickly, and so the walls are going to become a candidate.
Some masonry walls can hold more water than they get hit with
Well, where’s the drainage planePath that water would take over the building envelope. Concealed drainage-plane materials, such as building paper or housewrap, are designed to shed water that penetrates the building’s cladding. Drainage planes are installed to overlap in shingle fashion (weatherlap) so that water flows downward and away from the building envelope. in a masonry wall like this? You know, this is four layers of stone. Well, one percent of the water passes through the first layer, and then one percent of the one percent passes through the second layer, and then one percent of the one percent of the one percent passes through the third layer, and by the time we get to the fourth layer there isn’t any stuff passing through. So the water is leaking in, but it’s stored and dissipated. We have what we call a very large hygric buffer. Water enters, but it’s stored in the mass of the assembly. And the assembly is moisture-tolerant enough to deal with it, as long as we don’t put what on the inside? VinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). wallpaper.
And it would be really stupid in that wall to put steel studs on the inside, insulate the steel studs with fiberglass, and cover it with what? A plastic vapor barrier. That would be a stupid thing. Could you insulate it on the inside? Well, it would be real nice to insulate it with a couple of inches of foam. The high-density foam probably wouldn’t want to go more than three inches, because it’s three perms per inch and so it’s a vapor retarder rather than a vapor barrier. With the low-density foam you could go to ten or twenty inches. If that doesn’t make sense, you could go as much as you possibly wanted as long as you had the space. But you probably don’t want to put something on the inside that doesn’t breathe at all.
Ugliness is not sustainable
So what’s the likelihood of wrapping the outside of this beautiful stone building with a membrane, putting insulation on the outside, and adding vinyl siding? This is why we don’t do things just for energy conservation reasons, because that would make the building what? Really ugly! And ugly is bad. Beautiful is good.
In fact, I wouldn’t let them touch the walls at all —until after they did the roof, until after they did the foundation, until after they did the windows, until after they did lighting, and the heating, and mechanical systems. And over my dead body, then, maybe then, would I let them do something with the walls. In fact the only thing that I would like them to do is maybe re-point the mortar and the joints. I know I’m not going to completely stop water, but I’m going to maybe reduce it. And later on, when we talk about retrofits and foundations, John will talk about how important it is to get the chemistry of the mortar that you’re going to use for re-pointing just right.
Insulation can cause water problems
Are there negative consequences that are associated with adding thermal resistance to the interior? Is that going to change other factors? (Remember we talked about drying potential.) Can I add too much insulation, or sufficient insulation that the water content in the masonry stays high enough, long enough, to hurt the masonry? And the answer is Yes. I can cause problems with freeze/thaw. I can also enhance problems with osmosis and efflorescence and other issues.
So the question is, “Well, how much insulation can I add before I get into trouble?” And you’re going to hate this answer, or love this answer depending on whether you’re a client or a consultant. The consultant's answer is, “It depends." And you should pay me to tell you what it depends on because it depends a great deal on where you are, and what’s going on. The client hates that, because the client would like to know, well, what?! All right, well, what does is depend on?
Well, freeze/thaw damage isn’t a problem if water doesn’t saturate, or wet your claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. system or your wall system. And so the best, most effective way of dealing with freeze/thaw is all of these wonderful water-shedding elements. You can insulate walls to a great extent if water isn’t concentrated on the surfaces. And so there’s a big difference between something with wonderful drainage mechanisms all over the façade, versus a very smooth, brick veneer, for example. And it’s one of those judgment things that I can look at a building and say, Wow, this is really well drained. I’m not going to have water concentrated, or running down one aspect of the façade.
Now, usually an old building will tell you if it has those problems, because you walk around the building and you look at the stain marks. Right? So the first thing that you do before you do any insulation, is you install your drip edges, you deal with your flashings, you deal with the rain shedding things that will basically kick the water off of the surface. So if the water isn’t concentrated, you’re never going to have a freeze/ thaw problem.
Location matters too
What’s the next issue? Well, you don’t even have to do that if you’re in that part of the country where it doesn’t rain. There’s much less of a problem with freeze/ thaw in Edmonton than in Montreal. Both are cold, miserable, disgusting places, but one has more rain than the other, one has more likelihood of surfaces getting wet.
So what’s the other factor? Well, we have rain, concentration of water on surfaces — you also need cold temperatures. It’s rare that we have to worry about freeze/thaw problems in places like New Jersey and New York City. I don’t think we have much to worry about in Boston. But I’d be real nervous in Burlington, Vermont, and I’m real nervous in Ottawa, and I’m kind of semi-nervous in Toronto. And so, in most of the United States there isn’t an issue with respect to insulating these mass assemblies on the interior.
So this is more of a Canadian issue, and a Northern New England issue, and a Minnesota issue than it is a Chicago issue, a Boston issue, a New York City issue, a Philadelphia issue. OK, can I insulate a wall on the inside in Boston that’s a mass assembly? I’m going to say, pretty much yes, with a restriction in terms of R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. . Should I have a vapor barrier on the inside? No, you shouldn’t. And it would be nice to keep water from being concentrated on the surface of the building. When we start getting into, say, Portland, Maine, I’m going to say you probably shouldn’t insulate more than R-10. What’s that based on? A gut feeling. I have a really big gut, I’ve been around a long time, and it’s an intuitive, experience-based thing. I’ve looked a buildings a long time, I know what works and what doesn’t based on what I’ve seen out there.
The secret lives of consulting engineers
Now people always ask us to do a calculation, and I’m sort of saying, why? Why don’t you trust my judgment and intuition? Well, the sophisticated client will — because they know that if we generate a calculation, it’s going to be based on what? Intuition, judgment, and experience, right? You know, the unsophisticated client, we love them — especially if they have money — because we get to do what? Take it.
And you know, basically we write up a report. We do a wonderful simulation, and it looks really slick. There’ s all kinds of numbers and equations in there, and at the end of the day we know it has the right answer — because we knew the right answer before we started. And the right answer came to us from what? Our observation and experience. We worry a lot about this stuff in Montreal and Ottawa, we’re nervous about it in Toronto, we’re not nervous about it in Boston at all, cause we know exactly what we have to do in Boston to never get in trouble: Control the flashings and the rain water, don’t put a vapor barrier on the inside. Knock yourself out, re-point your joints — you’re done.
It’s so difficult in Ottawa and Montreal, and we generally don’t comment on it, because we don’t know what the answer is. We let other people take the risk and we watch them, right? Because how many times is a client going to hire you when they ask you a question, and you say, “Shoot, I don’t know. Let’s try this and see what happens.” That would be the honest thing to do, and when have you ever had a consultant tell you that? The honest thing?
We did a retrofit of a bakery that in Newark, New Jersey, with two inches of high-density spray foam, and then an inch and a half metal stud with gypsum board. What a slick way of doing stuff. Now, are we doing that kind of stuff in Burlington, Vermont? The answer is, Well, yeah. But how come I’m not worried about it? Well, two or three buildings I’ve been involved with, the folks really went to a lot of effort to ensure that the parapets were properly flashed, that the windows were properly flashed, that we had drip edges, and so that we weren’t concentrating the water on the surface. When we did that, we unhesitatingly said, “OK, now you can insulate with the closed-cell high-density foam, because we don’t have the risk of water leading to this damage.”
At the end of the day: no water, no problem.
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