2927 -- Effect of an Exterior Air-Infiltration Barrier on Moisture Condensation and Accumulation within Insulated Frame Wall Cavities PDF

Increased airtightness of buildings has been promoted for energy savings. One method for achieving greater airtightness is the installation of an air-infiltration barrier on the exterior of building sheathing. Although most barrier materials promoted for this application have a high water vapor permeance, it has been a concern that such installations could lead to moisture problems.

To evaluate the potential for such problems, a series of laboratory tests were conducted. One such series involved the condition where warm and moist indoor air circulates through wall cavities. To simulate this condition, three wall segments were installed in an environmental chamber, warm moist air was circulated by fan through three stud spaces, the wall segments were subjected to temperature differentials, and the moisture content of the sheathing and insulation was measured before and after each test. The tests were conducted first on the wall segments without the air-infiltration barrier and were then repeated with a barrier installed.

The results indicate that the air-infiltration barrier installed between the sheathing and the siding causes a more even moisture distribution by decreasing the accumulation of condensation in building materials in areas of high moisture content and by increasing it in areas of low moisture content. It was also observed that the hightest moisture content in the sheathing occurred under moderately cold conditions, while the highest moisture accumulation in the fiberglass occurred under more severely cold conditions.

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