Once upon a time, house insulation meant an extra sweater — and stop your damn complaining. Men were men, women were women, and cats and dogs were cats and dogs, I assume. Houses included features to produce and retain heat, of course — things like double back-plaster walls and central chimneys. But until the 20th century, insulation barely existed in any formal sense.
One thing that invariably surprises people when I walk them through a house during their first blower-door test is how much air leaks in through the electrical switches and receptacles. On a recent Friday, we went out to do the last home energy rating in our latest HERS rater class, and we got to see something even better. But first, let's talk about that air leakage. We have a number of surprises waiting.
Blower doors are spoken of in reverential tones in energy circles. Or at least they were a few years back. Now you can’t throw a manometer without hitting a contractor setting up a blower door. Which is a very, very good thing.
With the incorporation of air leakage standards into various housing codes, blower doors are becoming essential. In fact, I tell customers that a simple shorthand for whether your insulation contractors grok building science is whether they own/use/understand blower doors.
No, it’s a huge deal. The photo (right) is of air streaming through recessed lights in a cathedral ceiling.
I often and exhaustively speak about air sealing as if it were a universal good. And it is, right up there with brown ale and Avengers movies. My audit customers often look confused when I address their insulation questions by bringing up air barriers and air leakage. I mean, “Why are you talking about air leaks when I asked about the insulation?”
In last week's blog, I suggested that talking about infiltration rates in terms of air changes per hour isn’t an accurate way to portray air leakage. The problem is that you’re dividing by volume but the leaks happen at the surface. I don’t think ACH50 is going away anytime soon, and I use it myself because everyone else does, even though it’s biased toward larger houses.
During the Westford Symposium on Building Science in 2010,* I was watching the tweets from the people who were there. At one point, I saw this one: “@EFL_Guy: ‘Air leaks through surfaces, not volume’ Joe Lstiburek.” I'd been meaning to blog about this issue for a while, so I wrote an article about it. Now, a couple of years later, it's time for a little update.
At the 2012 Passive House Conference in Denver, Dr. Joseph Lstiburek gave the keynote address for the opening plenary (or plenum, as Henry Gifford would say) session. His words, clever as always, added some nice historical perspective to what the Passive House folks are doing but also caught some people off guard.
Read on, and I'll tell you more about that.
The new Brattleboro Food Co-op building with affordable housing on the top two floors is nearly completed, and we’ll be shopping there in just a week or two. So, how did the building turn out? Were the goals achieved? Are the mechanical systems going to work as intended? How effectively was the building envelope constructed?
Whether you want to build a new home or fix an old one, the way to ensure that you get the best performance is to do the building envelope right. That means installing the right amount of insulation and installing it well, and it means having an air barrier with minimal leakage. But how do you know when you've done enough air sealing? How tight is tight enough?
Recently, I wrote a little article about the stack effect to explain that the flow of air and heat is upward in winter but downward in summer. Turns out, the stack effect is a hot topic. That article has gotten 25 comments so far. When I posted it to the RESNET BPI group on LinkedIn, it got another 22 comments.
Posted on April 26,2015 by Tristan Roberts in air barrier
From an energy-efficiency standpoint, the trouble with owning an old home is that you’re stuck with whatever bad decisions the previous owners made, and historical trends also tend to work against you. The trouble with building a new home is that you are the one that is going to make the bad decisions.
The best opportunity to make important decisions that will deliver energy efficiency for the life of the home is during design. There is rapid diminution of these opportunities during construction and then during use of the home.
Posted on April 26,2015 by Tristan Roberts in air leak
Whenever we’re working on the outside of a home—the roofing, siding, or site—my uncle Chris will remind me to think like a drop of water. Mentally tracing how a raindrop is likely to travel down a building, and including details to move it off and away, is a simple exercise that is too often ignored.
Today, though, we’re going to talk not about water but about air. I have a new exercise to propose to Chris: think like a wisp of air.
Our development company has been working with several builders, including our own parent company, to determine the factors that affect our blower-door test results.
The following list includes things we have learned to do, and things we have learned not to do, to achieve an optimal blower door test result. (We aim to achieve the Passivhaus standard of 0.6 ach50.)
Homes insulated with fiberglass batts are leakier than homes insulated with cellulose or spray polyurethane foam. Until recently, fiberglass batt manufacturers shrugged off the damning air-leakage data, insisting that their batts could deliver the R-value promised on the packaging — and then changed the subject.
One of the most cost-effective ways of lowering residential energy costs is to reduce a home’s air leakage rate, so it makes sense for energy codes to ratchet up air-sealing requirements. The latest (2009) version of the International Residential Code does exactly that.
UPDATED on December 12, 2014
Builders of a certain age — say, those older than about 55 or 60 — started their careers at a time when no one talked about air leakage or air barriers. Back in the early 1970s, even engineers were ignorant about air leakage in buildings, because the basic research hadn’t been done yet.
Times have changed, and most residential building codes now require builders to include details designed to reduce air leakage. Today’s young carpenters are working on job sites where air barriers matter.
Beefing up R-values and reducing air leaks are the twin rallying cries of builders focusing on energy efficiency. Regardless of the particulars of the house design, more insulation and fewer air leaks make houses more comfortable, more durable, and less expensive to heat and cool.
No one seems to argue that point. But Al Cobb wonders which is more significant.
The oil price shock of 1973 sparked a burst of interest in “solar houses.” During the 1970s, owner-builders all over the U.S. erected homes with extensive south-facing glazing — sometimes sloped, sometimes vertical. Many of these houses included added thermal mass — concrete floors, concrete-block walls, or 55-gallon drums filled with water.