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Must Houses Breathe?

Paul Kando

Yes, insists the old saw. Indeed, leaky houses have few common moisture problems. However, they also waste a lot of energy, requiring more fuel to make up for all the lost moist warm air. Builders of a century ago must be forgiven: They didn’t know any better, and heating fuel was plentiful and inexpensive. Not any more.

Way too much breathing
photo credit: Green Building Advisor

Our challenge with old houses is to make up for their built-in defects,. without demolishing what’s there and starting from scratch, especially since old houses vary widely. The average Maine house loses over 1/3 of its heating energy through air leaks, but, house to house, the range is 2% to 68%. So each house requires a somewhat different approach, built around the idea of comfort.

Comfortable houses do not leak, they are energy efficient. Our physical comfort depends on (1) whether we are absorbing or losing heat, (2) whether moving air blows on or away from us, (3) whether we are absorbing or losing moisture, and (4) whether our surroundings are healthy and safe, beginning with an ample fresh air supply. Common sense suggests that to make our house comfortable we must, first, control the flow of heat, air and moisture and, second, provide external energy as needed for heating, hot water, lights, cooking and other necessities.

Unfortunately the typical American house has these priorities backwards: it relies on once-inexpensive heating fuels to make up for its failure to control heat, air and moisture flow. Most of our houses are under-insulated and leak air like a sieve. Moisture freely moves around the house in the form of vapor until the heated air that absorbed it cools. Then the vapor condenses, usually where we do not want iy, like inside walls, on the underside of the roof, on windows, doors, walls and ceilings. Liquid, moisture can cause mold and rotting of the structure – damage often unnoticed until it requires major repair.

What to do? Smart folks who build new, only build the most efficient: super-insulated, air-tight, without thermal bridges through the framing, with heat recovery ventilation and good windows. In existing buildings the principles are the same, but specific details must be tailored to the individual situation. For this reason, reducing heating costs begins with assessing the energy performance of the home. Only an energy audit can reliably provide this information, including an estimate of how the cost of every step taken will be paid back from energy cost savings within a reasonable time.

Common sense suggests that we treat our current energy bills as our energy budget – the $2,000 to $3,000 spent on fuel last winter. We can keep spending this budget on fuel, year after year, or spend some part of it on measures that permanently reduce our fuel consumption. One thing is certain, the longer we delay to “reprogramming” our energy budget in favor of permanent improvements, the more money we waste. The good news is that even the least of us can prevail, even if we must start small. Only the procrastinators can’t help losing.