What a blower door test measures in a hot-humid climate

What the number is

The test depressurises (or pressurises) the house with a calibrated fan mounted in an exterior door and records the airflow required to hold a set pressure difference across the enclosure. The result is normally reported as CFM50 — cubic feet per minute at 50 pascals — and converted to ACH50 using the conditioned volume.

It is a whole-house aggregate. It tells you how much leaks, not where. Finding where requires the test to be running while someone walks the building with a smoke pencil, an infrared camera, or a hand.

Why it reads differently in climate zone 2A

Most published guidance on air sealing was written from a heating-climate perspective, where the leakage penalty is heat loss and the moisture drive runs outward. The corridor from Austin to San Antonio is hot-humid climate zone 2A, where the dominant drive for most of the year is inward, and the air being pulled through the enclosure carries latent load with it.

That changes what a bad leakage number costs you. In a cold climate a leaky house is expensive. In a hot-humid climate a leaky house is expensive and it is continually importing moisture into wall cavities and interior spaces, where it has to be removed by something.

What a tight house then requires

Tightening the enclosure removes an uncontrolled path for outdoor air. It does not remove the need for outdoor air. Once the leakage rate drops, ventilation has to be designed, sized, and commissioned deliberately, and in this climate that ventilation air usually needs its moisture managed before it reaches the occupied space.

This is the point where the blower door result stops being a score and becomes an input to the mechanical design. A tight house with an undersized or uncommissioned ventilation strategy is a worse outcome than a leaky one, and we treat the two as a single scope rather than two line items.

How Sage Co. uses the result

We test at least twice: once at the pre-cover stage, while the air barrier is still reachable and a defect can be fixed for the cost of an afternoon, and once at completion as a record. The pre-cover test is the one that changes the house; the final test is the one that goes into The Sage Co. Record.

The final test is performed by an independent third party. Sage Co. does not grade its own homework — an internal role can record that a test happened and what it showed, but only the independent verifier can mark the result independently verified.

A failed test is not deleted or replaced. It stays in the record alongside the remediation and the retest, so the house's history is legible to whoever owns it next.