Keep Breathing: The Evolution of How Homes Breathe
If you’re considering a major remodel or new home project, be prepared for your architect to talk “Building Science.” You will learn about mechanical systems and materials that you have never heard of and may seem more like a luxury than a necessity. I hope to convince you that they’re actually both.
The 80’s were a really strange time — in a lot of different ways. In the home building industry, new materials emerged and gained widespread use very quickly. Pneumatic nailers took the place of the good ole hammer and nails, and building schedules became turbo charged while budgets got slimmer. With the energy crisis of the late 70s in the review mirror, the word “efficiency” usually referred to time and money while the idea of energy consciousness felt like a bummer for most people.
Before this time, most of the raw materials that went into a home’s skin and bones were un-engineered wood. There was some insulation, but it was rudimentary and installed without much precision. Water and vapor made it into the wall and roof cavities all the time, but the materials were so porous that smaller moisture problems had a way of naturally fixing themselves without much notice.
During the 80’s, new materials and methods drastically changed the way homes adjusted to moisture and temperature variations. When water and vapor found its way into the walls, it became trapped. Increased resin levels in plywood kept moisture inside the walls, and new types of membranes and siding often did the same thing. Homes could no longer breathe and dry out on their own. As a result, black mold and sick building syndrome raised their ugly heads in the residential construction world.
To many, this was (and still is to a few holdouts) a very loud “I told you so” to the new building science camp. There’s a major catch to that argument, though: All of that air that was passing through our walls to dry them out was also stealing energy. 30-40% of the energy loss from a 1980’s era home is from air leakage. That number, while acceptable in 1985, demands our attention today.
This may seem strange to you, but consider this: Washington State Energy Code’s minimum air leakage number is five air changes per hour in a simulated average wind. Even when your home meets code, the air in your house is replaced five times per hour with outside, unconditioned air. And your system has to heat or cool that air to make it comfortable.
The solution has emerged in the residential industry all over the world: Build air-tight, super insulated homes and outfit them with efficient forms of mechanical ventilation. This might not jive well with your initial intuition. Clients ask us all the time: What’s energy efficient about a ventilation fan that runs all the time? Why do I build an airtight home then poke a bunch of holes in it? The guys in the white coats have considered all of these things, but the real proof is in the energy bills and mold-free homes
Building high performance homes is only partly about adding insulation. The primary issue on your builder’s mind should be moisture management. Thankfully, today’s building wrap systems allow vapor to pass through while blocking air and liquid water (think Gore-Tex in hiking boots). A Heat Recovery Ventilator, or HRV, is an efficient fan that brings in outside air that is filtered and pre-conditioned, while exhausting the moist air from your bathrooms and kitchen. These things are usually low-tech but cost more than a code-minimum setup. In the long run, your home, wallet, and health will thank you.