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Blower Door

Today, many builders are routinely building houses that are very airtight, often without realizing it. The common use of building wraps, moisture barriers, high efficiency windows and even simple plywood sheathing all have direct effects on reducing air leakage and infiltration. An airtight house has many fewer openings through which fresh air can enter. Without the addition of mechanical ventilation, a tight house can result in stagnant air, less natural ventilation and dissatisfied homeowners. On the other hand, houses with large amounts uncontrolled air leakage are equally troublesome with comfort complaints due to drafts, building failures and high energy bills.

Despite the growing importance of house airtightness, few builders, architects or homeowners know how tight their houses are. Until recently, the building community has tended to rely on subjective estimates of airtightness. Unfortunately, it is impossible to accurately estimate the tightness level of a building by visual inspection alone. And without knowing the airtightness level, it is difficult or impossible to design for effective approaches to ventilation and air quality, or to accurately diagnose performance problems.