ShareThisBuild It Tight, Ventilate It Right: Part 1
What is the difference between air tightness, air infiltration, & air leakage? People often make the mistake of thinking that an airtight building is a ‘stuffy’ building. This is not necessarily the case nor is it the intent of creating air tight structures. Airtightness is NOT the measurement of the amount of fresh air available to the occupants, but rather is the measurement of how much air will leak into and out of the home through undesirable locations, such as small cracks and holes in the building shell.
All buildings have to be ventilated for health and comfort and airtight buildings are no different. Airtightness is achieved through careful implementation of strategy throughout the design and construction phases.
Air leakage is the undesired and uncontrolled movement of air in to and out of a building which is not for the specific and planned purpose of exhausting stale air or bringing in fresh air. Air leakage is called “infiltration” (air moving into a building) or “exfiltration” (air moving out of a building).
Why is air tightness important?
Air leakage is a major cause of energy loss. Typically between 30% - 50% of heat loss can be attributed to air leakage. Air leakage has also been shown to reduce the effectiveness of thermal insulation by up to 70% and so it is clear that energy efficiency is greatly affected and influenced by airtightness.
Air leakage can also lead to other building and comfort problems such as drafts, frozen pipes, ice damming, moisture movement (creating mold and compromised air quality), and ultimately building failure due to rot and decay.
Different weather conditions affect air leakage as well, with heat, cold, or windy conditions leading to more infiltration. Air infiltration also can contribute to problems with moisture control. Warm moist air leaking out of a home may meet with cold surfaces causing condensation, which could then lead to moisture in walls and other undesired places. Moldy and dusty air can enter into a leaky home as well.
How is air tightness accomplished?
Prevention is cheaper and easier than cure. The recommended strategy in both new and old homes is to reduce air leakage as much as possible and to provide controlled ventilation as needed. Properly air sealing cracks and openings in your home can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment. Many holes connect the various components of a building; i.e. plumbing, electrical and HVAC holes through walls floors and ceilings, connecting crawlspaces to main living areas, garages to main living areas, and main living areas to un-conditioned attic spaces. All of these connections contribute to compromised air tightness. Properly addressing these areas and air sealing where appropriate could save hundreds of dollars in heating and cooling down the road as well as create a more durable home.
About the Author
“The recommended strategy to reduce air leakage in both new and old homes is to provide controlled ventilation.” Controlled ventilation can reduce pollution in the house, but it does not reduce leakage. The only way to reduce leakage in the house is to make all holes in the house air tight. The easiest way to make a house air tight is to put it in a large poly bag and tie the top with a twist tie. The bag must be kept warm so that condensation does not occur on the cold plastic, this requires at least twice (three times in extreme climates) as much insulation on the cold side of the poly as is on the warm side of it. I have found that the most effective way to get this amount of insulation is to strap the walls and roof with dimensional material supported away from the poly a distance that will allow glass or mineral fiber insulation of sufficient thickness to achieve the two or three times R value. This povides support for siding and roofing to be applied.
Doing this will result in a reduction of heat loss from the house by about 85%