The Science Behind Air Leakage Testing | Build Show Podcast Ep 214

The Energy Conservatory is the company behind the Minneapolis Blower Door; founder Gary Nelson didn't invent the blower door but was its "Henry Ford" — he made it cheap and practical enough for builders to use in the field, not just researchers.

Code, not builder enthusiasm, has driven airtightness improvements — Sweden required a blower door test and a 3 ACH50 limit on all homes back in 1976, decades ahead of the U.S. patchwork of state requirements.

Even where blower-door tests are in code, enforcement is spotty — the guests estimate only about half of U.S. homes built in 2025 were actually tested, because small-town inspectors often don't enforce it.

Airtightness is about far more than energy: it drives air quality (keeping out pollen, radon, and insects — "bug sealing"), comfort, quieter interiors, and durability by controlling moisture-laden air.

Air transport, not vapor diffusion, causes most durability failures — air carries roughly ten times more moisture through the envelope than vapor permeance does, so sealing air and water matters far more than obsessing over house-wrap perm ratings.

The biggest remaining new-construction problem is the envelope/HVAC interaction — ducts in a hot attic depressurize the house (about 3x more leakage with the system on, up to 9x with bedroom doors closed), undermining even a well-sealed envelope.

Sell better buildings the way Yeti and Tesla sell — on lifestyle, health, comfort, and safety, not on energy-savings ROI — because that's what homeowners actually care about.