Failed Your Blower Door Test? Here’s What to Do

Drywall is up, paint is on, the inspector is coming, and the blower door test came in over your target. You are not the first builder to be in this position, and the 2021 WSEC-R has paths to keep your project moving without tearing anything out. This page walks through what your numbers actually mean, what credits you can still claim, and where to make the trade-off if you have to.

What is the maximum ACH50 allowed in Washington?

Per WSEC-R Section R402.4.1.3.1, the maximum air leakage rate for any dwelling unit under any compliance path is 4.0 air changes per hour at 50 Pascals (ACH50). This is a hard ceiling. If your test result is above 4.0 ACH50, you cannot pass under any path until you find and seal more leaks.

If your test result is 4.0 ACH50 or below but higher than the number you committed to on your permit drawings to claim an R406 credit, you have options.

How do R406.3 Category 2 air leakage credits work?

R406.3 Category 2 is where tighter-than-code air leakage earns energy credits. The 2021 WSEC-R Table R406.3 lists three options. You may pick only one.

A few important notes:

• The credit values in this table are for "All Other"occupancies — single-family detached, duplexes, townhouses, and R-3. Group R-2 multifamily buildings have their own column with the same option structure but different credit point values.
• All three options also require an HRV at the listed minimum sensible heat recovery efficiency. If your project does not have an HRV, you cannot claim any credit in this category.
• The permit drawings must explicitly call out the option being claimed, the maximum tested air leakage, and show the qualifying HRV system. Plan reviewers check this.

What can I do if my blower door test missed the credit target?

Say your permit drawings claimed Option 2.2 (1.5 ACH50, 75% HRV, 1.5 credits) and your final test came in at 1.8 ACH50. You have three reasonable paths.

Option A — Find more leaks

The cheapest fix if your number is close. Common late-stage leakage sources:

• Attic hatches and pull-down stairs without proper gaskets
• Recessed light fixtures that are not IC-AT rated
• Electrical panel penetrations on exterior walls
• Plumbing chases between floors
• Dryer vent and bath fan housings

A smoke pencil or theatrical fog source plus the blower door running in depressurization mode will show you where the air is actually coming in. Most failures of less than 0.5 ACH50 over target can be closed in a half-day with caulk, foam, and gasket.

Option B — Step down to a lower-credit option and make up the difference elsewhere

If you cannot close the gap, drop to the option you actually achieved. In our example, 1.8 ACH50 with a 75% HRV qualifies for Option 2.1 (1.0 credit) instead of 2.2 (1.5 credits). That leaves you 0.5 credits short of your permit commitment.

Make up the 0.5 credits in another category. Common options that are still possible after rough construction is complete:

• R406.5 Efficient Water Heating — upgrading from a standard electric tank to a heat pump water heater is often a same-day swap and earns 1.5 credits.
• R406.8 Energy Star Appliance Package — installing the Energy Star-listed package can earn 0.5 credits if you have not yet selected the appliances.
• R406.6 Renewable Electric — a small solar PV array (usually only worth it if you were already considering solar).

Talk to your AHJ before changing your R406 selections — most are cooperative if the math works.

Option C — Apply AeroBarrier

AeroBarrier is a sprayed aerosol air sealant that drops ACH50 dramatically in a single application. WA installers exist (Western AeroBarrier, Smart PNW, United Seattle Aeroseal). Typical cost in Washington for a new-construction application is $1.00–$1.50 per square foot of conditioned floor area. It works on completed houses but adds prep cost; it is most cost-effective applied at dry-in before insulation.

If your test is significantly over target — say 2.5 ACH50 when you committed to 1.5 — AeroBarrier is often cheaper than tearing out drywall to access framing.

How can I prevent a blower door failure on the next project?

The cheapest blower door fix is the one you do not need. Plan the air barrier as a continuous detail from the foundation up: sealed sill plate, sealed rim joists, gasketed top plates, taped sheathing seams, sealed penetrations. The crew that air-seals as they go almost always passes on the first test.

If you are at the start of a project and want help planning the credit selections so your blower door commitment matches what your crew can realistically deliver, run your project through the WSEC.ai wizard — we will show you the credit math on every option.