Can a Home Be Too Tight?

Sometime during your crusade to seal those energy robbing cracks and holes in your home, you're bound to start asking yourself, "Isn't air flow important for a healthy home?  Can I take this whole thing to the extreme?"  The answer - it depends.

While it's true that air flow from clean locations prevents pollutants like dust and mold from reaching unhealthy levels, a leaky home provides no assurance that indoor air pollutants are properly eradicated: during periods of calm weather with no wind, for example, air can sit stagnant in a leaky home for days.  On the other hand, during a windy day in the winter, a leaky home effectually needs to be re-heated from scratch every few hours, which is a waste of both energy and money.   So the best way to ensure that a home is both healthy, safe, and energy efficient is to air seal the home as well as possible, and to pair air sealing efforts with increased mechanical ventilation to make sure that air cycles in and out of the house at a healthy and consistent rate.  When sealing a home the last leaks you want to seal are those directly from the outdoors, the first leaks to be sealed are those from the attic and crawlspace (air most of us would prefer not to breath).

                                      This Chart shows leakage paths in a sample of New California Homes.air leakage paths california new homes

Ventilation standards like ASHRAE 62.2 (adopted into California Code) are largely designed for newer buildings that have average air leakage.  California homes have a repuation for being tighter than most homes.  Recents studies have shown a 1600% variance between the tightest and leakiest new homes built in California.  This indicates that there is little testing and a whole lot of guessing when it comes to how leaky or tight we build houses.  If we are guessing at that, we are also problably guessing at whether or not we need mechanical ventialtion and if so how much.  As the chart above indicates our guesswork often leads us to take our "fresh make up air" from the worst possible locations like attics and crawl spaces.  That's true for old homes and new homes alike. 

The best thing you can do as a homeowner to ensure that your home is as energy efficient and as healthy as possible is to talk to your home energy auditor about where you should focus your home improvement efforts.  But as a basic premise, as the mantra goes, "seal tight and ventilate right."

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