Q. Will My Home Be Too Tight? Doesn’t My House Need to Breathe?
A. Yes, a house requires a certain amount of ventilation to maintain good quality indoor air, to expel moisture, and for the health of the overall structure. However, you want controlled ventilation, not uncontrolled air infiltration. Modern building science has attributed a whole host of problems and failures to uncontrolled air infiltration. Often the underlying cause of these failures is due to a “leaky” building envelope that allows moisture-laden air to pass through the cavity and condense on cold surfaces.
A house insulated with fiberglass has anywhere from 0.5 to 0.6 natural air changes per hour (meaning 50-60% of all the air in the house is replaced every hour). A tight house using spray foam has approximately 0.1 to 0.15 air changes per hour. No matter how tight we make a house, doors and windows still leak air. Therefore, a house built with spray foam still breathes, just at a more controlled and practical rate. This is important because the Department of Energy estimates that air-leakage accounts for up to 40% of energy costs.
Building a tight house allows us to have better control over the artificial indoor environment that we create. We can control where, when, and the quantity of fresh air that is introduced into the home. This leads to greater control over the quality of the air and the moisture loads in the air. Furthermore, because of increased allergies, people are finding the need to separate themselves from the smog, pollen, mold, and spores prevalent in outdoor air. Spray foam, coupled with proper mechanicals and ventilation, creates an extremely sophisticated indoor environment with unparalleled levels of control. Mechanical ventilation should be introduced to help achieve an acceptable level of air quality.
“A home built to the American Lung Association® Health House® guidelines is constructed airtight to improve energy efficiency and prevent unplanned moisture movement. Although many stories in the media attribute indoor air quality problems to houses being built too tightly; the reality is that homes need to be as tight as practical… Moist air leaking out in cold weather can condense on wall and attic surfaces, creating mold growth and…structural decay. This is a direct result of the home not being tight enough. Moist air leaking into a home in hot humid weather can have the same effect… Air leaking into a home from an attached garage has been shown to be a significant source of Carbon Monoxide.”
American Lung Association