Sealing Out the Drafts

Winter has arrived yet again, and our struggles to maintain an efficient - and more importantly, comfortable - 100-year old home continue. This is a battle I wage with elements every year as things turn cold.

This year, I've become increasingly knowledgeable about a little thing that is hard to see and really adds up - air. Or more specifically, air leakage, an important aspect of green building. Although we performed a blower door test over a year ago, there continue to be opportunities to improve the air leakage in our home.

So after learning some building science, its useful to know that in addition to heat rising, the upper levels of a home are constantly under more pressure. Heat and air both rise, creating a chimney effect in a mult-level home. This static pressure causes air to want to find its way out of the house, particularly in second floor converted attic like we have.

With this in mind, I recently went around our second floor to address these air leakage issues. The largest losses on the second floor are in all the ceiling penetrations. The recessed lighting cans and built-in speakers have been great and provided clear headroom, but when installing them we could have been a bit more careful. The biggest regret I have is buying the big-box special recessed lighting housings. We purchased the insulation contact (IC) rated housings, which were important so insulation could come right up alongside the lights. However, had I spent a dollar or so more on each light housing, we could have had air-tight insulation contact (ICAT) housings. As this article explains, regular recessed lights allow for a ton of air leakage. Note to self: when buying these in the future, hold up to the light in the store. If light comes through, so will air!

Oh well, fortunately, many of our recessed lights in the attic have an air-tight shower trim kit. We liked them because they have a flat, not-quite-interrupted surface. Now, I'm glad they help fend off air leakage too. Additionally, I recently took to time to caulk between the drywall and the metal can to eliminate further leakage around the cans.

While I was messing with the ceiling, I also took down the smoke detectors (we have 3 upstairs). Underneath one of the smoke detectors, there was a significant amont of dust - enough to form a ring around the collar! I knew it would take more than Wisk to make this ring go away. Dusty signs like this - after just two years since installation - is a tell-tale sign that there is some major air leakage and heat loss ocurring here.

After removing the smoke detector mounting bracket, I pulled out one of my new favorite stocking stuffers, Dap Latex Foam Sealant, a great easy-cleanup spray foam that is water-based instead of oil-based (like Great Stuff).

I also used the spray foam around some of the air return ducts that weren't sealed to the drywall, and plugged a few other holes with what remained in the can.

After all of this, I think our second floor bedrooms in the converted attic space will be more comfortable this year. And, this may be a surprise, but this will likely make the basement more comfortable as well. Why? Well what happens in the basement has everything to do with what happens in the attic.


It goes back to that static pressure concept - when air is lost through the attic,
it comes in at a lower level such as a basement or, even worse, an attached garage (think of all the chemicals and fumes stored in a garage, and how that air might come in if the attached garage is the weakest link in the air barrier). We are fortunate to have a detached garage, so we don't worry about this. However, if we make it harder for that static pressure to force air up through the attic, it means less air will be pulled in from the basement, keeping that a bit cozier and healthier too.


All in all, it took more time to write about this than it did to actually seal up some of these holes, so I'm hopeful we'll get a more comfortable home with this small investment. With the Chicago winter underway, every little bit of comfort and energy savings helps Humphrey House be a happier and greener home!

Discovering Where our Energy Dollars Go

We've taken the summer off of blogging, but things are starting to pick up again here at Humphrey House. Sorry for the delay, but life happens sometimes. Anyway, I recently borrowed my friend Jim's blower door as a sort of DIY energy audit, looking at the overall "tightness" of our home.

For those unfamiliar, a blower door is basically a high-powered fan that sits in a tarped-ff doorway. You close all the windows in the building and turn this sucker on High. This will suck the air out of the house, and then start pulling air in from outside the home through any cracks and crevices. The fan is attached to an air pressure gauge monitoring both indoor and outdoor pressure, to ensure the home is depressurized to around 50 Pascals (Pa). At this level, noticeable drafts occur. [More info]

Once I had this setup and running in our kitchen doorway, I went around the home looking for obvious air drafts. Our house is now littered with pieces of blue masking tap indicating all the leaks and drafty spots in the house that should be sealed up before winter comes along. Most interesting finding: the older windows did not leak around the window sashes so much as they leaked around the frame. For example, more air moved from a gap underneath the window stool (interior window sill) between that and the piece of trim below the window (the window apron).

The really cool techie thing about the blower door test is the fact that with the gauge, you can tell just how leaky a building is. Despite consciously remodeling with energy efficiency in mind, I knew that I'd be in for some surprises. After all, we're living in a home built 100-years ago, when there was likely no insulation, and air barriers were really more like "hair barriers".

So, the air pressure gauge measures the volume of air moved out of the home. As you may recall from high school, volume is usually measured in cubic terms. In this case, we're looking at cubic feet of air, but we want to know that over time. So the gauge tells at a certain air pressure (50 pascals) how much air is moved in a minute (CFM)? Well, in our 1.5-story home, it's around 4400 CFM.

What does this number mean in real terms of how leaky the house is? Well there's a rough back-of-the-envelope calculation that can make this more meaningful. (Math Warning!)

We need the volume of air in the house. Given the average 8-foot ceiling height and 3500 sq ft of living area (2135 above ground + 1365 finished basement), we have about 28,000 cubic feet of air in the home. (Humphrey House air volume = 3500sf x 8ft = 28,000 cubic feet).

We can find out how many times the air in the house turns over per hour by taking the air pressure gauge measurement, 4400 CFM, multiply by 60 minutes to convert to hours, and then divide by the air volume in the home: (4400 CFM x 60 M) / 28,000 cubic feet = 9.4 air changes each hour (ACH).

You might be tempted to say, "That's one leaky house!" but remember, this is at a high pressure of 50 pascals. We can "normalize" that number by using a factor for a well-shielded home in an urban area to find the natural air changes (ACHn). For simplification purposes, we'll use a factor of 16.7 (this is derived from LBL empirical data). So we divide our 9.4 ACH by 16.7 to arrive at a normalized air exchange of 0.56 ACHn.

This means roughly 1/2 of the air in the house is changed over every hour. For comparison, the 1989 standard for air exchanges recommends 0.35 ACHn. So, in other words, despite soy foam in part of the house and other energy efficiency efforts, we're still pretty leaky.

We have a lot to do to air seal the home, but thankfully the blower door helped us find all the little holes where our energy dollars were flying out the house. Next step is to work on fixing them. If you're interested in getting a detailed analysis like this of your home, follow the directions on EnergySavers.gov, or find a professional energy auditor at natresnet.org or www.bpi.org. If you're in Chicago, look at any of these.