Your test is done, the report is in your inbox, and it’s full of numbers that all look important. Many teams skim straight to “pass” or “fail” and miss what the data says about the envelope. Others compare ACH75 commercial air leakage results to residential ACH50 targets and draw the wrong conclusion. Those mix-ups can slow closeout.
We wrote this blog so owners and GCs can read their results with confidence. You’ll learn what each metric measures and why the spec usually cares about one of them. You’ll also learn how to read a pass or fail and what a result means for remediation. Keep reading to get more from every report you receive.
A commercial air leakage report summarizes a whole-building fan pressurization test, usually run under ASTM E779 or ASTM E3158. We push the building to a range of pressures and record airflow at each point. Then we calculate the flow at 75 pascals. Residential tests use 50 pascals and a volume-based target, so those numbers don’t transfer. Commercial specs measure a larger, more complex shell. They need a metric that stays fair from a two-story clinic to a mid-rise office.
CFM75 air leakage is the raw airflow, in cubic feet per minute, needed to hold the building at 75 Pa. It shows total leakage, but a bigger building will always post a bigger number.
ACH75 divides that flow by building volume and converts it to air changes per hour. It’s useful for comparison, but it can mislead large buildings. Volume grows faster than surface area, so big buildings tend to look tighter than they really are.
That’s why most commercial specs use the normalized leakage rate. This divides CFM75 by the full envelope area, including walls, roof, and the lowest floor. The result is air leakage per envelope area, stated in cfm/ft² at 75 Pa. It ties leakage to the surface that actually separates inside from outside.
Your spec sets the threshold. Common targets fall between 0.25 and 0.40 cfm/ft² at 75 Pa, depending on the code or owner standard. A result below that line passes.
When interpreting blower door results, commercial teams should also check the test’s uncertainty. A result sitting right at the limit may call for a closer look before anyone signs off.
A narrow fail usually points to targeted fixes. Crews often find the leaks at roof-to-wall joints, penetrations, or door frames. Smoke tracing or infrared scans under pressure help them find those spots fast. A large miss often signals a wider air-barrier problem, such as missing transitions between systems. That calls for a broader review before retesting.
Before you focus on the final number, confirm these three items:
Check which surfaces went into the area total. Leaving out the slab or roof raises the normalized rate. Counting interior walls lowers it. The area should match the method your spec defines, so the comparison stays fair and defensible.
Look at wind, temperature, and baseline pressure readings. Also review how well the data points fit the curve. A strong fit and stable conditions mean you can trust the result. Poor conditions may explain an odd number and justify a retest.
Many specs average both directions. A big gap between them can reveal flaps, dampers, or loose membranes that move under pressure. That pattern helps crews target repairs, and it can explain why the averaged result lands where it does.
Air Tight Solutions is a leading provider of energy efficiency testing and compliance services for new construction. Our BPI-certified team uses calibrated multi-fan equipment and knows IECC requirements across many code editions. Every report we deliver explains ACH75 commercial air leakage, CFM75, and normalized results in plain language, so your team knows exactly where the building stands.
We don’t hand off a report and walk away. We review the results with you, point out likely leak sources, and help you plan a fast path to a passing retest. Learn how we support projects through our commercial air leakage testing, then let’s talk about your next building.
We don’t offer warranties. We measure and document your building’s air leakage accurately, so your team has reliable data for decisions and final sign-off.
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