We like to think of homes as impermeable. After all, that’s why we have them; to keep the rain, wind, and cold out. Not to mention insects, small animals, and pollen clouds.
But the truth is, your home’s shell is a membrane. It breathes, just like you do. (That’s a good thing!) Every home does it. The important question is not if your home leaks, but how much.
To figure out if our new house had an appropriate level of breathability, we contracted with our local energy company to get a complete home energy audit. Professional energy auditors have a bunch of tools that let them measure exactly how much air is leaking into (or out of) your home, and even pinpoint where the worst leaks are.
You don’t necessarily need to hire someone to do an energy audit. For the motivated home owner, a DIY home energy audit is quite feasible. HouseLogic has tips for doing it yourself: DIY Home Energy Audit: 6 Easy Steps.
We chose to go with a pro, in part because our energy company offers a discount. Your utility may offer free energy evaluations or give a rebate against the price of a pro audit, too
What the energy auditor did
Walk-through. Our auditor started by doing a walk-through of the house and looking for visual clues of air leakage. Anyone with one good eye could walk through our house and notice that mice/cats/babies have eaten away at a few of the window sashes. In the winter you could stand next to any closed window and feel a little like Marilyn Monroe.
But the inspector noted something I wouldn’t have: cobwebs. Walking past one of the basement windows, he pointed to a tangle of spider webs and said cobwebs are usually a good indicator of air leakage. Spiders build them where there’s plenty of insect movement, and that coincides with gaps in windows.
Blower-door test. It’s a way of measuring precisely how much air leakage a home allows. It’s done by first closing all the doors and windows in the house, then setting up a powerful fan at one of the first-floor openings (in our case, the front door).
Then, the inspector turns on the fan while at the same time measuring the change in air pressure within the house.
The idea is to measure how much air the fan needs to move to create a pressure differential between the interior and exterior of the house. In a very leaky house, the fan needs to work hard and move a lot of air before a pressure differential is achieved. In a tight house, it doesn’t take much to depressurize the interior.
A commonly used blower door metric is the airflow at a specified building pressure (normally 50 pascals). Our home measured at 4,600 cubic feet per minute at 50 pascals (meaning: to get the house pressure to 50 Pa, the fan had to move 4,600 cu. ft. per minute).
Just for reference, here’s the chart that came with our final report:
Note how the chart only goes up to 4,000. We were literally off the chart in terms of air leakiness. Not good.
Infrared camera. Next, the inspector left the blower door test running while we walked through the house with an infrared camera. That let us see all the places where cold air was running into the house.
The pictures taught me a surprising lesson: The bulk of a home’s air leakage isn’t through the windows, but through the walls. Like many people, I assumed the best thing we’d be able to do to seal up the house was to replace the windows. But on the infrared camera, you could easily see how much more leakage there was directly through the exterior walls. And since walls occupy a far greater surface area than windows, they have a greater impact on your energy efficiency.
Our energy fix-it list
Our energy audit report came with a great list of recommendations for things to fix. Even better, there was a handy list of home improvements that were eligible for rebates through our local energy provider.
Check to see if your state or city government, or your energy company, is offering rebates, tax credits, or low-interest financing for energy improvements; you’ll be surprised how much help you can get. A great source for rebate info is the Database of Incentives for Renewables and Efficiency.
For our home, the biggest offender was air leakage. So we plan on hiring a contractor to seal the attic bypasses, chimney cavity, and rim joist.
The next biggest win for us will be to add insulation to the walls (they currently have an R-value of 5; the inspector recommends getting to 14).
We’ll replace the 30-year-old, 60%-efficiency furnace with a brand new, high-efficiency model. Rebates are available for anything higher than 90% efficient, but we’ll probably go with a 96% efficient model (there seem to be diminishing returns once you get past that point).
Looking ahead, once we get the home all snug and warm, our only problem will be to make sure we leave enough ventilation to let sufficient fresh air into the house. And maybe we’ll leave a few gaps open for the spiders, too.
This is a post in the Curbly House series! Follow along as we document every step of our complete home makeover, from gutting the walls to putting up the finishing touches. And don't forget to let us know what you think in the comments!