Air / Moisture Infiltration & Water Absorption

May 5, 2011Leave a reply

Air infiltration can account for as much as 30 to 35% of heat loss / gain in a building envelope(1,2). Most conventional insulations offer very little resistance to air infiltration, relying on other building materials such as drywall, poly, and sheathing to combat air leakage. The integrity of these air barrier systems is often compromised over time through a combination of installation deficiencies, and normal household activities (e.g. screws, naills, etc.). As a result, air can be transferred through the building envelope, resulting in convective heat transfer.

Often times, this air contains moisture which can condense within the building cavity, deteriorating the building structure and leading to potential mold and mildew problems. In addition, the performance of most conventional insulations may be compromised if they become wet since water is a good thermal conductor.

Water Absorption: A process by which water permeates into a substance.

IMPACT: Water is not a very good insulator. As a result, water absorption accelerates the rate of heat transfer via conduction through an insulation material. In addition, water absorption may compromise the physical stability of the insulation, resulting in swelling or sagging.

Air Infiltration: The amount of air leaking into or out of a building mainly through cracks in walls, windows, and doors.

IMPACT: Insulations may perform at a fraction of their nominal thermal resistance if air infiltration occurs. Air infiltration can account for 30 – 35% or more of a buiding envelope’s cooling and heating costs and can contribute to problems with moisture, noise, dust, pollutants, rodents and insects(2)

(1) NAIMA Pub. No. BI 480 6/99 “The Facts About Insulation and Air Infiltration”

(2) Technology Fact Sheet “Air Sealing – Seal Air Leaks and Save Energy”, USDOE

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