Air tightness: the cheapest energy measure there is
Up to 40 percent of a home's heat loss is air leakage, not conduction. Sealing the envelope usually costs less than adding insulation and saves more.
Where the heat actually goes
A building loses heat three ways: conduction through the assemblies, radiation through the glazing, and air simply moving through gaps. The third is the one most easily overlooked because it does not show up in an R-value calculation.
Air leakage also carries moisture. Warm indoor air moving into a cold cavity deposits that moisture where it condenses, which is how a leaky wall becomes a wet wall.
How it is measured
A blower door pressurises the building and measures the flow needed to hold a pressure difference, usually 50 or 75 pascals. The result is expressed as air changes per hour or as flow per square foot of envelope.
The US Army Corps protocol sets 0.25 cfm per square foot of envelope at 75 pascals, which is among the strictest widely applied requirements in US construction and the reason air barriers became a delivered result rather than an intention.
Airtight does not mean unventilated
A tight envelope needs designed ventilation, which is the fourth passive house principle: balanced heat- and moisture-recovery ventilation. Tight and ventilated gives better indoor air than leaky and unventilated, because the air comes in where you chose, filtered, and with its heat recovered.
What Guardian publishes
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Guardian states that up to 40 percent of a home's heat loss is due to air leakage, and that Shield™ buildings have a superior envelope with minimal air infiltration.
Source · Products page, lasting cost savings
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The Shield™ specification references the U.S. Army Corps Air Leakage Testing Protocol; Guardian's market material states an air-tightness test guaranteed pass.
Source · 3-Part Specification 1.3 H; Market page
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Written by Data Subsystems, for Guardian Structural Technologies. Last updated .
Drafted from Guardian Structural product literature and published building-science sources. Awaiting Guardian technical review. Confirm any figure against the current product documents or ask us before you rely on it in a design.