Florida’s threshold is 7 air changes per hour at 50 pascals. That is a more forgiving number than the 3 ACH50 used in colder climate zones, and most competently built Florida houses clear it without heroics. The houses that fail almost never fail because of the wall assembly or the windows. They fail because the air barrier was nobody’s specific job, and a dozen small holes added up while everyone assumed someone else had handled it.
What follows is what we actually see on site, in the order it costs you money.
1. Decide who owns the air barrier
This is the whole thing, and everything below is a consequence of it.
On a house that passes easily, one person can point at a drawing and trace the air barrier around the building without lifting their finger. On a house that fails, the framer assumed the insulator would seal the top plates, the insulator assumed the drywall contractor would, the drywall contractor assumed it was already done, and the HVAC installer cut a hole through all of it on Tuesday.
Name the trade responsible for sealing each plane, put it in the scope, and the rest of this article mostly takes care of itself.
2. Seal the ceiling plane, because that is where your air is going
In a Florida house with a vented attic, the ceiling is the air barrier, and it is the leakiest surface in the building by a wide margin. Hot air rises into a 130-degree attic and pulls replacement air in through everything below.
The specific offenders, in the order we find them:
- Top plates. The gap between the top plate and the drywall, running the entire perimeter of every interior and exterior wall. It is a small gap multiplied by hundreds of linear feet.
- Recessed can lights. Even airtight-rated housings leak at the trim if the trim is not seated. Non-rated housings in a vented attic are open holes.
- Bath and kitchen exhaust penetrations. The duct gets sealed to the fan housing and the housing never gets sealed to the drywall.
- Plumbing and electrical penetrations. Vent stacks, wire bundles, anything passing from a wall cavity into the attic.
- The attic access hatch. A weatherstripped, latched, insulated hatch versus a sheet of plywood resting in a frame is a measurable difference on the test.
- Dropped soffits and chases. A soffit above the cabinets that is open to the attic at the top is a chimney with a decorative face on it.
3. Treat the garage wall as an exterior wall
The garage is outside the thermal envelope. The wall between it and the house is an exterior wall that happens to be indoors, and it gets treated like an interior partition more often than not.
Seal the top plate above that wall, seal every penetration through it, and weatherstrip the door. It matters beyond the test number, too. That wall is also what keeps car exhaust and stored chemicals out of the house.
4. Do not let the HVAC installer undo the envelope
Every register boot, refrigerant line set, condensate line and thermostat wire is a hole through the air barrier. Each one is small. There are thirty of them.
Boot-to-drywall joints in particular are worth specific attention, because they leak into the test twice: once as envelope leakage, and once on the duct leakage test. Sealing them properly improves both numbers with the same tube of mastic.
5. Get the details right before drywall, not after
Almost everything above is a twenty-minute job with the framing exposed and a genuinely expensive one after the ceiling is closed, painted and trimmed. This is the argument for a pre-drywall air sealing walk on any plan you have not built before: one hour, before the drywall truck arrives, catching the things that would otherwise be found at final.
On a production plan you have built twenty times, you already know where it leaks. On a custom house or a first build, you do not, and the test is an expensive place to find out.
6. Have the house genuinely ready on test day
A house that is not ready does not produce a bad number. It produces a wasted trip, or worse, a bad number that sends everyone chasing a problem that does not exist.
- Windows and exterior doors installed, operable and closed.
- Drywall complete, with penetrations sealed.
- Insulation installed.
- HVAC installed, with registers and grilles on.
- Plumbing traps filled or capped. An open drain line is a direct path to outside, and this is the single most common cause of a surprise failure.
- Attic access in place.
- Power available for the fan.
- Exterior doors staying shut for the few minutes the fan runs.
7. Schedule it with room to fix something
Booking the test for the same morning as your final inspection is how a two-hour air sealing job turns into a week of delay. Leave a few days. If the house passes, and it usually does, you have lost nothing. If it does not, you have a problem instead of a crisis.
8. Know your target before you test
7 ACH50 is the prescriptive code threshold. But if the house is going through the R405 performance path, the energy calculation may have committed you to something tighter, and that number is the one that counts. Read the Form R405 before test day rather than after, and send it over with the booking so we test against the right target.
If it does fail
It is not a violation. It is a measurement that has to improve before the report can be submitted. What decides how expensive it gets is how fast you find the leaks, which is why a test that tells you where the air is going is worth more than one that just hands you a number and leaves.
Most failures we see are fixed the same day with a few tubes of sealant, a weatherstripped attic hatch and someone paying attention to the top plates. Then we run it again.
Related
For the mechanics of the test itself, see the blower door testing pages or the complete FAQ. For what changes when the 9th Edition takes effect, see 2026 Florida Building Code Energy Conservation: What Builders Need to Know.
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