Envelope Leakage Testing in Florida: A Complete Guide for Homeowners and Builders

If you’re building a new home in Florida — or even renovating one substantially — you’re going to run into envelope leakage testing. It’s required by the Florida Building Code, your inspector won’t sign off without it, and a failure can stall your certificate of occupancy.

This is the most common service I run for builders in Marion County. Here’s exactly what the test is, what it measures, what the code requires, and how to make sure you pass on the first visit.

What is envelope leakage testing?

Envelope leakage testing is actually two separate tests bundled together: a blower door test that measures how much air is leaking through the building envelope (walls, ceilings, floors, windows, doors), and a duct leakage test that measures how much conditioned air is escaping through your HVAC duct system.

Both tests use precision fan equipment and pressure gauges to put the house or the ductwork under a known pressure, then measure how much air the fan has to move to maintain that pressure. The more leakage, the more air the fan has to push.

These tests aren’t about comfort. They’re about code. Florida adopted them because uncontrolled air movement is the single biggest driver of energy loss in residential construction — bigger than insulation, bigger than windows. A house can have R-30 ceiling insulation and a fancy heat pump and still bleed conditioned air through a dozen unsealed penetrations in the attic.

What the Florida Building Code requires

The Florida Building Code, Energy Conservation section, sets specific limits on both whole-house infiltration and duct leakage for new residential construction. Builders need to hit both numbers before the certificate of occupancy can be issued.

For the blower door test, the limit for the building envelope is measured in ACH50 — air changes per hour at 50 Pascals of pressure. Florida currently caps this at 5.0 ACH50 for new construction. That means at a 50-Pascal pressure differential, the house can lose at most 5 times its interior volume of air per hour.

For the duct leakage test, the measurement is CFM25 — cubic feet per minute of leakage at 25 Pascals. Florida limits total duct leakage to 4% of conditioned floor area for ducts inside the conditioned space, or stricter limits depending on configuration. A 2,000 square foot home, for example, can have at most 80 CFM25 of total duct leakage.

These numbers aren’t suggestions. If the home exceeds them, the test fails and the issue has to be corrected before retesting.

How the blower door test works

The technician mounts a calibrated fan inside an exterior door, sealed into the doorway with a fabric shroud. All exterior windows and doors stay closed. All interior doors stay open. HVAC supply and return registers stay open. Any combustion appliances (water heaters, gas fireplaces) get checked and isolated.

The fan then depressurizes the house to 50 Pascals — about the same as a 20 mph wind blowing against every exterior surface simultaneously. As air gets sucked out of the house, replacement air pushes in through every crack, gap, hole, and unsealed penetration in the envelope. The fan measures exactly how much air it has to move to maintain that 50 Pa pressure.

The result is converted into ACH50 using the house’s interior volume. That number gets written on the report along with pass/fail against the code limit.

A typical test from setup to result takes about 45 minutes for a single-story home, longer for two-story or complex layouts.

How the duct leakage test works

The duct leakage test uses a different piece of equipment called a duct blaster — a smaller calibrated fan that connects directly to your duct system, usually at the air handler or a central return. The supply and return registers throughout the house get temporarily sealed with tape so that the only path for air is through the ductwork itself.

The duct blaster pressurizes the duct system to 25 Pascals, and the gauge measures how much air the fan has to push to maintain that pressure. Any air leaving the system before reaching a sealed register is leakage. The result reports in CFM25.

We run this test in addition to the blower door because ducts and the envelope leak differently and at different points in construction. A house can pass the envelope test and fail the duct test, or vice versa.

Common causes of envelope test failures

In my experience testing homes in Marion County, the failures cluster around the same handful of problems:

Attic hatches and pull-down stairs. These are almost always under-sealed. Builders install them, the drywaller cuts in around them, and nobody comes back to weatherstrip the perimeter. A 22”x54” attic stair with bad seals can be 50-80 square inches of open hole into the attic.

Recessed light fixtures. Standard recessed cans (non-IC-rated, non-airtight) leak directly into the insulation and from there into the attic. Each can might leak 10-30 CFM at test pressure. A house with twenty recessed lights in the ceiling can lose hundreds of CFM through them alone.

Top plates. The wood top plate where exterior walls meet the ceiling needs to be sealed to the drywall. Often it isn’t. Air follows the wall cavity up and exits at the unsealed top plate joint.

Plumbing and electrical penetrations. Every wire, pipe, and vent that passes through the top plates, exterior walls, or floor system is a potential leak. Foam sealant is cheap. Unsealed penetrations are expensive in test failures.

Garage-to-house wall. The wall between an attached garage and conditioned space gets cut up with framing, wiring, water heater installs, and dryer vents. Each penetration leaks if not sealed.

For more on the patterns we find across Marion County builds, see our common energy problems article.

Common causes of duct test failures

Duct test failures usually come from one of a few places:

Unsealed connections at the air handler. The plenum-to-air-handler joint and the boot connections to the trunk are high-leakage spots if not properly sealed with mastic.

Loose or disconnected duct sections. Especially in attics, ducts can shift during construction and develop separations at joints. Flex duct in particular is prone to losing connection at the inner liner while the outer wrap appears intact.

Damaged ductwork. Anything that crushed, punctured, or stepped on a duct during construction will leak. We see this most often near attic walkways and HVAC platform edges.

Panned floor joist returns. A practice still common in older homes — using the open cavity between floor joists as a return duct — is essentially impossible to seal completely. New construction avoids this, but renovations sometimes inherit it.

How to prepare for the test

The biggest preparation step is timing. The envelope test should happen after the house is dried in and all major air sealing is complete — typically after insulation but before final paint and trim. The duct test should happen after ducts are fully installed and sealed but ideally before drywall closes up chases.

Other prep:

• All HVAC registers and grilles open
• Attic hatch fully closed and weatherstripped if applicable
• Combustion appliances accessible for safety isolation
• Exterior doors and windows fully installed and closeable
• Anyone working in the house knows the test is happening so they don’t open exterior doors mid-test

We arrive with all the equipment. The builder or homeowner doesn’t need to provide anything except access.

What happens if a test fails?

Most failed tests can be fixed without major rework. We identify likely sources during the test using smoke tracing — a non-toxic smoke that visually shows where air is moving — and we report exactly where the leakage is concentrated.

Common fixes:

• Sealing the attic hatch with foam tape and weatherstripping
• Air-sealing recessed cans with caulk and gaskets (or replacing with airtight IC-rated fixtures)
• Foam-sealing top plates and penetrations
• Mastic-sealing duct connections that failed

After repairs, we retest the same day or the next day depending on schedule. Most failures can be turned into passes in a single retest.

What you get from us

For every test, we provide a signed compliance report that includes:

• Measured ACH50 and CFM25 values
• Pass/fail against current code thresholds
• Reference to the specific Florida Building Code section
• Notes on test conditions (temperature, wind, equipment used)
• Tester certification number

That report goes directly to your inspector. Marion County inspectors are familiar with the format and the testers in the area.

Frequently Asked Questions

How long does an envelope leakage test take?

Plan on 1.5 to 2 hours on site for both the blower door and duct leakage tests combined, including setup and breakdown. Single-story 2,000 square foot homes are on the faster end. Two-story or 3,000+ square foot homes take longer.

When during construction should the test happen?

After the house is dried in, insulation is installed, and major air-sealing work is complete — but before final trim, paint, and flooring. For the duct test, ideally after duct installation and sealing but before drywall closes off chases. In practice, both tests often happen together near the end of construction.

What does the test cost?

Pricing depends on the size and complexity of the home. For typical single-family new construction in Marion County, the combined envelope leakage test (blower door plus duct leakage) is a flat-rate service. Contact us for a specific quote.

What if my house fails the test?

A failed test isn’t a project killer. We identify the leakage sources during the test using smoke tracing, you address the worst offenders, and we retest. Most failures pass on the first retest after typical attic-hatch and top-plate sealing fixes.

Do I need to be on site during the test?

Someone with site access needs to be there — typically a superintendent, builder, or homeowner. You don’t have to watch the test, but we’ll walk you through the result before we leave and email the signed report the same day or next business day.

Does Florida actually enforce these limits?

Yes. The Florida Building Code Energy Conservation section requires both tests for new residential construction, and the certificate of occupancy is tied to passing them. Marion County inspectors do verify the signed test report before issuing the CO.

What’s the difference between this and a home energy audit?

Envelope leakage testing for new construction is a code-compliance test with a specific pass/fail threshold. A Home Performance and Comfort Assessment for an existing home uses the same blower door and duct equipment but is a diagnostic service — it tells you what’s wrong and what to fix, with no pass/fail threshold.