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Blower-door-directed air sealing


Although many homeowners assume that the most significant air leaks in their home are around windows and doors, hidden leaks in a basement or top-floor ceiling are usually more significant. To find these hidden leaks, air-sealing contractors use a blower door. To find out whether his own house was leaky, GBA managing editor Dan Morrison invited John Jennings, an energy consultant from Steven Winter Associates, to bring a blower door to Dan’s Cape Cod house. Once the blower door was installed and operating, technicians checked for air leaks in every room of the house.

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The leaks that matter are up high and down low

Air sealing work usually begins in the attic. (During the winter, the stack effect pushes indoor air into the attic through unsealed cracks, while pulling outdoor air into the basement or crawl space.) The existing attic insulation is temporarily peeled away, exposing the partition top plates. Sealing the gaps between the partition top plates and the drywall cuts down on air leaking into the attic. These gaps are sealed with spray foam. While the insulation is pulled back, workers also seal around plumbing vents and electrical cable. Down in the basement, it’s important to seal air leaking through cracks around the mudsill and rim joist. After obvious cracks have been sealed, a second blower-door test is performed, to measure the leakiness of Dan’s newly tightened house. For more information on blower-door testing, see “Blower Door Basics.”


Daniel Morrison, Thanks for coming over today, John. We’re going to do an energy audit, and I was just curious how I can make this house more efficient. It’s a Cape, and I plan to do a lot of remodeling. Right now, I’ve got some concerns about air sealing.

John Jennings, Steven Winter Associates: Well, if nothing else, we’ll be able to evaluate how the house is performing right now. Under the program that we’re here for, which is the Home Energy Solutions Program—it’s sponsored by United Illuminating and Connecticut Light & Power. And I believe Connecticut Light and Power is your utility?

D: That’s my utility.

J: So, we’re coming out here to first evaluate the house for a number of things. The first thing we’re going to be doing is—you see it here—a blower door. It’s a large fan that can either pressurize the building, as if you’re blowing up a large balloon, or depressurize it so that it’s pulling air from the outside cracks, and it goes through the fan. The gauge here measures how much air is going through, so we can find out how tight or how leaky the house is. If the house is tight enough, we’ll let you know and we won’t go any further. But if we find the house needs to be tightened up and made more energy efficient, the fan doesn’t just measure the leakage in the house; it gives us the ability to go around and find where those leaks are. When we first go up into an attic—and that’s the first place we want to hit—the areas we seal are the top plates, both interior walls and outside walls. Where the actual plates in the attic can be exposed and where the Sheetrock meets on both sides, there’s usually a gap that we can foam—and any electrical wiring, we can foam.

D: So, we can find where the big cracks are.

J: Exactly. And even some of the little ones. We’re able to test the entire shell of the house. Once we find the leaks, our crew will actually go through with different types of caulks and different types of foams to seal those leaks. Once we’re finished, we do the test again. We always test our way in and test our way out to know how the house is performing before we do anything, and then to see how successful we were afterwards and to make sure we didn’t do anything wrong or harm the house. We try to stop the stack effect, which is cold air coming in from the bottom of the house—through the foundation, usually—and then pushing up just like a chimney and trying to get out.

D: OK.

J: Once we’ve done all the work we feel we can get, we’ll do a final test to see exactly what we did, and we’ll make sure that we leave you the results. And also, we like to encourage the homeowner to go around with us as we’re looking for leaks, just so they can see what we’re doing. It’s pretty straightforward, but since we’re in their home, we want them to understand it better.

D: Great.

Insulation Options for a New Dormer

Daniel Morrison, And so, John, what I want to do is make a shed dormer all the way across the whole back of this house, probably starting in a foot and a half or so, clear back. We’ll move this kneewall out 2 or 3 feet.

John Jennings, Steven Winter Associates: So the whole back of this house will seem like a two-story colonial.

D: Basically.

J: Other than like a foot or two in on each side.

D: Well, it’ll step in from the back—but we’re in 4 feet, so we’ll move this wall out and we’ll move this up to be sloped. And we’ll probably do the same on that other end. Where should my thermal envelope be?

J: Well, it depends on…let’s start with the roof first. You have a couple of options. One is to have a flat with a roof above it. So, the plaster would be here, and a few inches up, or a foot or so up, we would have the roofline. So, you want it where you want the heat to stop. It would be the Sheetrock in that situation. The other thing to consider is maybe making the shed follow the roof, so it’s somewhat cathedral. That way you can have a variety of different types of insulation. One is just standard insulation; it can be blown, it can be wet spray cellulose, it can be fiberglass batting—making sure it’s installed properly, making sure there’s a good air barrier and/or vapor barrier. And just follow the roof, what they call a hot roof. So, basically you have your Sheetrock, then your insulation 6 to 8 inches thick or more, and then you have your roof; there’s no air space. In those situations, as long as you follow code, there’s no need for typical attic ventilation like soffit vents and a ridge vent, because there’s no cavity to ventilate. It’s full insulation.

D: That ought to make my job easier.

J: One concern I have about what you said is the dormer is going to go out, the full shed dormer, but it’s not going to meet up with the exterior wall on the outside; it’s going to be recessed a little bit. Do I understand that right?

D: It’s going to be a step back, yeah.

J: That’s attractive; I think that’s a nice way to go. But the concern about that on an existing home is you have some insulation out in your current kneewall floor. If that end piece isn’t addressed to be fully insulated and have a proper air barrier in each bay, you may have air moving in between floors still, like you have now. So, make sure whoever does it pays attention to fully insulating that, and since insulation is not an air barrier unless it’s rigid foam, you want to have an air barrier. You can have rigid blockers in each bay, making sure that kneewall is insulated all the way out to the exterior wall, cause down below is your kitchen. So, if you don’t insulate it properly and you just have an air barrier where your dormer is, that insulation will still allow warm, moist air to get up on the underside of that roof.

D: And so it’s not just keeping the cold out, it’s keeping the warm, moist air from getting inside my cavity… [unintelligible].

J: That’s exactly right, because that’s exactly what will happen. It will get into the cold cavity, and it will hit the plywood or the roof deck or the exterior wall, and it will turn right back into water. Now, you may not see it happen for a while because it depends on how cold it is, it depends on how much moisture you have in the house, and how much is trying to drive out there. But it’s a real easy fix, and you can put a plywood blocker—anything solid that will stop air—plywood, rigid foam insulation, which does both: insulates and acts as an air barrier. There are special cardboard baffles that you can get from the building supply industry; you just staple in place and seal around them with caulk or foam, anything like that. Some people want to use plastic, and that’s not a good idea because it’s hard to put in, it’s real flexible, you can’t seal it well, and it has no insulating value. So, anything rigid that you cut to fit, you seal around it…

D: Put foam around it…

J: Exactly.

Identifying Existing Insulation

OK, what we’re doing now is checking for wall insulation. We just drill a small hole in an outside wall, and then we use nothing more basic than a wire coat hanger; it’s got a hook on the other side. We’ll put the coat hanger in, and we twist to find insulation. So, it’s as we suspected. And the reason we know that it’s batted is because as we go through with the probe, we can feel the kraft paper that’s on the inside closest to the Sheetrock. We go all the way out so we can bring it back, and then we just measure this: It’s a 4-inch cavity. Now we know how deep the cavity is, and then—just make this a little bit bigger—we get our hook in here. That gives us the ability to pull the insulation out so we can show it to the homeowner. So now we know it’s not full because as we twisted the coat hanger, we could feel where it had no resistance to where it finally found resistance, which means it found the fiberglass. Then the hook will actually pull the insulation out so we can see if it’s fiberglass, rock wool, mineral wool. It’s not a fiberglass, although it’s a spun wool; it’s either a rock wool or a mineral wool batt. So, nothing more than a wire probe and a drill bit will get you a lot of information.

Insulation Choices for a Garage Workshop

John Jennings, Steven Winter Associates: OK, so how are you going to be using this space?

Daniel Morrison, I’ve got some power tools set up. I’m probably going to have it be a workshop whenever I get it cleaned out.

J: So, it’s not going to be used as a garage ever—it’s not going to be part garage, part workshop.

D: No, it’s mostly going to be conditioned space.

J: That’s good to know.

D: So, where’s my thermal boundary here? Right now, it’s supposedly here, but I’m thinking I want it on the walls and around the perimeter.

J: Well, that’s actually a good point, and it’s not a black-and-white answer because sometimes people have workshops that have absolutely no heat, so that would still mean that if it’s not warm down here, your thermal boundary would still be what is currently the garage ceiling. This is unconditioned space; it might be used, but it’s still unconditioned. Now, in your boiler room, the boiler’s giving off heat, so there’s no reason to separate that area because the standby loss is heating that basement or keeping it mild in temperature. So, the thermal boundary in your basement is really the perimeter and the walls. Since the walls are primarily below grade, I would be concerned about the rim joist or the band joist, making sure it’s both tight and well insulated. Fiberglass is an easy way to do it, and the two-part foam is a very good way of sealing that band joist because it’s kind of in a tight area. Regular foam may not get in there. Now, for out here, if this were mild in temperature in the winter—and by that I mean 60 degrees or warmer—I would not worry about this being the thermal boundary. Again, just like the basement, I would treat the band. And you could insulate the walls, but any of the walls that are below grade aren’t going to have much air infiltration getting through them. Insulating above—these walls are so thick—may not be that cost effective. And if you’re only keeping it 60, it’s good, because the floors aren’t too warm. But really, the difference between a 60-degree room and a 40-degree outside temperature—there’s not a lot of savings there; you’re not losing a lot. The other thing is, with this stone wall, if you use regular insulation, meaning fiberglass, and it touches it, you can draw moisture out of it, and it can get wet. Now, the fiberglass won’t get destroyed, but it will get soggy and lose its R-value. And then it can transfer the moisture to whatever your wall surface is. You could end up with some mold, so treating these walls is something that’s a little different. I don’t think it would be very cost-effective, but whatever you do, I’d make sure that if there were any insulation that touched it, it’s the type that wouldn’t be hurt by any moisture migration.

D: And they’re pretty thick.

J: They’re very thick. And it’s not like it’s a large room and you’re going to be heating it like a hothouse.

D: So, the band joist, the rim joist and maybe get a better garage door that’s…

J: Yeah, and the fact is you’ve got some good exposure here to the sun, so both daylight and possibly some passive solar gain, depending on what you put in there. Some people have, depending on how they use it, put in temporary rigid insulation panels where they can block it off just for the winter because they may want to open this up in the summer and get great ventilation. But you can also achieve that with patio doors.

D: French doors or sliders would be a good option?

J: I like French doors myself, not from an energy perspective, but they open up the whole opening, where sliders—you only have a half open at a time.

D: So, I can tell my wife that a professional said French doors or sliders would be a good option?

J: Well, I convinced my wife, so sure…

D: Thank you.

J: Just don’t give her my name.

Should You Upgrade Your Old Boiler?

Daniel Morrison, So, I called you here because I wanted advice about making my house super energy-efficient, and I expected you to tell me that this is the first place to start: the boiler that was put in when the house was built in the mid-1950s. But you don’t think this is really the place where I’ll get the most bang for my buck?

John Jennings, Steven Winter Associates: Well, this is a well-made boiler. Some boilers will only last you 20 years; it depends on the warranty. I’ve seen boilers that are converted from coal—that are 80 years old—and they’re still working properly. Not efficiently, but they’re working properly. And a lot of that is due to a combination of the boiler and the burner. While the boiler is original, your burner is a high-speed flame retention head burner, and those are much more efficient than the original shell heads, because basically what it does is break the oil into a spray faster. The oil actually breaks up and atomizes, so you can get more efficient use out of the fuel. And they also keep from sooting as much as the old burners did. The fact that you’ve got this equipment—even though this is older and there are newer systems out there—if you stay with oil, you’re probably going to have an efficiency somewhere in the low- to mid-80s. The brand-new ones are still working between 82% and 85%, which is good. The newer gas systems or some of the other efficient systems may actually be in the 90s, so they’re a little bit more efficient; but as long as you’re in the mid-80s, you’re doing pretty good. The thing is that this boiler is not one of the larger antiquated boilers, so it doesn’t have a lot of mass. Just replacing it may cost you a few thousand dollars, number one, and how much it saves is probably not going to be as much as you’d expect. It could be somewhere around 10% to 15 %; without someone evaluating that and testing a little more closely, you’re not sure. Other folks want to replace them simply because they’re old and they don’t know when they’re going to break. That happens with any old system, whether you say 15 or 20 years old—once it reaches that stage, it’s hard to say when it might fail, and that you have to replace it. It’s not something you’d like to do, but it’s a necessity because it’s leaking. As long as you have this cleaned on a regular basis, at least once a year, and let your technician take a look at it, you should be in good shape for a while. But, if you called me in 10 years and told me it was still working at the same efficiency, it wouldn’t shock me. And if you called me in 10 days and told me it developed a leak or it died, that wouldn’t surprise me either. So, it’s hard for me to say how much longer it will last. The interesting thing is your domestic hot water also comes from the boiler; it’s called a tankless system, and it’s not the most efficient way to get hot water. Some people will put in a separate water tank, either for storage or just a separate system that works on its own, simply because they don’t get enough hot water. But, in our conversations earlier, you mentioned how you’re getting enough hot water.

D: We’re getting plenty of hot water.

J: So, comfort’s not an issue, and replacing it could cost you—if you had a regular standard gas tank—anywhere from $500, to a special foam-insulated tank that’s called a storage tank or an indirect-fired water heater—those cost anywhere from a thousand to $1200 or $1500, depending on the plumbing; I can’t say exactly. The tank is pretty much like a Thermos bottle. The boiler still heats the water, but it dumps it into this superinsulated tank, and it only loses about a degree or two degrees for every hour that it’s holding the water. So, if you leave and you didn’t use hot water, the boiler’s not going to come on to replenish that water, because it stays hot for eight to 10 hours.


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