In the course of our home building and remodeling work we often hear folks state one version or another of the following building “truism”: “Walls gotta breathe.”
So old school! Okay, in one sense, they’re totally right. The traditional way of building does require leaky walls because those leaks accomplish two critical functions in traditional walls. The leaks:
- Maintain good indoor air quality by providing fresh air.
- Avoid moisture build-up by facilitating air flow into the wall cavity.
But from a green building perspective (or just a cost-savings one) the problem with the leaky-walls approach is obvious. Heated (or cooled) air that escapes through holes in the walls of a traditional home adds up to lots and lots of squandered energy. Hundreds of dollar bills are essentially being sucked out through those leaky walls.
Not good for the wallet or the planet.
Modern green building techniques make leaky walls oh-so-passe. Walls that incorporate vapor barriers and are designed to facilitate drying can readily address moisture concerns without depending on leaks in walls. So you can build or retrofit “tight” now without creating mold, mildew and rot problems. Home performance building science guides this approach.
But what about indoor air quality? How can we get the fresh air we need? Answer: move away from uncontrolled leaks and toward controllable and adjustable sources of fresh air:
- Install windows you can open.
- Use mechanical ventilation systems to deliver fresh air inside and exhaust stale air outside. Better yet, install a heat recovery ventilator (standard in Passive House projects) to minimize the loss of thermal energy that normally escapes with the exhausted air.
Simply put, walls don’t need to breath, but home dwellers do. The good news is that we don’t need leaky walls to get people the fresh air they require. Instead, we can create tight building envelopes with good windows and smart mechanical ventilation. That’s the green response to the “walls gotta breathe” myth.
-Zack
P.S. Thanks to Martin Holladay’s blog post “Ten Green Building Myths” for his treatment of the “walls gotta breathe” myth, as well as nine others.
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