Why Ocala New Construction Fails Blower Door Tests (And How to Fix It Before Final Inspection)
When a Marion County new construction home fails its blower door test, the cause is almost always one of seven specific air leakage patterns. Here's exactly where to look, how to fix each one, and what to expect on a re-test.
When a Marion County new construction blower door test comes back over the 5.0 ACH50 Florida code limit, the cause is almost never one big leak. It’s usually four or five medium-sized leaks adding up. The good news: the leak locations are predictable. After performing hundreds of tests on Ocala new construction, the same seven failure patterns show up repeatedly.
This article walks through each one — what it looks like, why it happens, and how to fix it — so builders can catch and seal these areas before the test is even performed. These are the same patterns that drive most of the common energy problems we find in existing Florida homes, just caught earlier when they’re cheap to fix.
How “Failing” Works in Practice
The Florida code ceiling is 5.0 ACH50 under any compliance path. In practice, most well-built Ocala homes test between 3.0 and 4.5 ACH50 on the first try. The marginal failures (5.1–6.0 ACH50) are usually fixed by sealing two or three specific leak points. The bigger failures (7.0+ ACH50) typically have multiple major issues — often missed during framing because the air barrier wasn’t planned as a continuous layer.
A leak-finding pass during the test identifies the major contributors. After sealing, a re-test confirms the fix. Most homes pass on the second attempt.
Failure Pattern 1: Plumbing Stack Penetrations Not Sealed
What it looks like: PVC vent stacks rise through the attic. Where they pass through the ceiling drywall, there’s typically a gap of 1/4 to 1/2 inch around the stack. Some homes have collar fittings; many don’t.
Why it happens: Plumbers cut a slightly oversized hole for the stack so it can be plumbed straight. The hole rarely gets sealed unless someone specifically addresses it as part of the air barrier strategy.
How much it leaks: A single un-sealed 4-inch plumbing stack can leak 15–25 CFM50.
How to fix: Spray foam in a can (low-expansion) around each stack at the ceiling. Takes 30 seconds per stack. Best done during rough-in by whoever’s responsible for air sealing.
Failure Pattern 2: Bath Fan Ducts Terminating in the Attic
What it looks like: The bath fan duct goes up into the attic, runs 6 feet sideways, and terminates with a damper at the soffit — or worse, just terminates open in the attic.
Why it happens: Code-required termination is at the exterior. Some installations terminate in the soffit (which is connected to the attic) or just stop short. The damper, even when closed, leaks.
How much it leaks: Each bath fan terminating in attic space can leak 30–50 CFM50. A 3-bath home with all three terminating in the attic can add 100+ CFM50 of unnecessary leakage.
How to fix: Run rigid duct through to a wall cap or roof cap that terminates outside. Use a damper rated for the application. Verify the connection at the exterior is properly sealed.
Failure Pattern 3: Top Plate Gap on Vented-Attic Builds
What it looks like: Where the interior wall meets the ceiling drywall, there’s a gap of 1/8 to 1/4 inch between the drywall and the top plate of the wall framing. In vented-attic builds, that gap leaks directly to the attic.
Why it happens: Drywall installers cut slightly small for tolerance. Mudded joints cover the visual gap but don’t seal the air leak.
How much it leaks: Each linear foot of un-sealed top plate gap can leak 0.5–1 CFM50. A 2,000 sq ft home with 200 linear feet of interior wall-to-ceiling joint has 100–200 CFM50 of cumulative leakage potential.
How to fix: Best handled during framing by gasketing the top plate before drywall, or by applying a continuous bead of acoustical sealant on the top plate before drywall is hung. After-the-fact fixes are difficult — usually requires lifting drywall edges and applying sealant.
Failure Pattern 4: Attic Access Hatches
What it looks like: A pull-down stair or a square panel hatch in a closet ceiling. The hatch sits on a wood frame; weatherstripping is either thin or missing.
Why it happens: Stock attic stairs and stock access panels don’t come with proper air sealing. The contractor installs what’s available and moves on.
How much it leaks: A standard pull-down attic stair leaks 20–40 CFM50 without weatherstripping. A square hatch leaks 10–20 CFM50.
How to fix: Replace with an insulated, gasketed attic stair (R-10+ insulated cover). For square hatches, add closed-cell foam weatherstripping around the perimeter and a positive latch to compress the seal.
Failure Pattern 5: Recessed Lighting (Non-IC-AT Cans)
What it looks like: Recessed can lights in the ceiling. Older or budget fixtures have holes for ventilation in the housing.
Why it happens: Non-IC-AT (insulation contact, air tight) recessed cans have intentional ventilation holes to prevent overheating. Those holes leak air directly to the attic.
How much it leaks: Each non-IC-AT can leaks 10–20 CFM50. A home with 20 recessed cans can have 200+ CFM50 of unnecessary leakage. This is easy to verify with infrared thermal imaging — the can lights light up as cold spots during testing.
How to fix: Specify IC-AT rated fixtures from the start. If they’re already installed, retrofit airtight LED conversion kits (sealed cans that fit into the existing housing). For specialty fixtures that can’t be retrofitted, build a sealed drywall box above each can.
Failure Pattern 6: Sliding Glass Door Frames
What it looks like: A standard sliding glass door at the back of the house. The track has weep holes that drain to the exterior. The track-to-frame connection often has small gaps.
Why it happens: Sliding doors are designed for drainage, not airtightness. The weep holes are necessary for the door to function (rainwater needs to drain out), but they’re an intentional opening between inside and outside.
How much it leaks: A standard sliding glass door can leak 30–60 CFM50, especially as the weatherstripping ages.
How to fix: This is one of the harder ones because the weep holes can’t be permanently sealed. Higher-quality doors (Andersen, Pella, custom impact-rated) leak less than builder-grade alternatives. Some builders specify French doors with multipoint locks for back-of-house openings to reduce this leakage.
Failure Pattern 7: HVAC Line Set Penetrations
What it looks like: The refrigerant lines (line set) from the outdoor condenser run through the wall into the air handler closet or attic. The wall penetration is typically a 2-3 inch hole with the line set running through it.
Why it happens: HVAC contractors cut a hole, run the lines, and move on. Sealing the penetration isn’t part of their scope unless specifically called out.
How much it leaks: Each un-sealed line set penetration leaks 10–25 CFM50.
How to fix: Spray foam in a can around the line set at the penetration. If insulation is needed, slip a foam sleeve over the lines first, then foam around the sleeve.
What to Do Before the Test Is Performed
If you want to maximize the chance of passing on the first attempt:
- Walk the attic with a checklist. Plumbing stacks sealed? Bath fan ducts terminating outside? Top plate gaps sealed at all interior walls?
- Inspect every penetration through the envelope. Plumbing, electrical, HVAC, exhaust. Each one needs to be sealed.
- Check the attic access. Insulated, gasketed, latched.
- Verify recessed cans are IC-AT rated. If not, plan for the additional leakage in your air sealing budget.
- Test pre-drywall if possible. Some Florida builders do a pre-drywall blower door to catch the framing-level leaks before they’re hidden behind walls. This is the cheapest fix.
For the broader picture of what testing looks like in Marion County, see our test day walkthrough article.
What Happens on a Failed Test
When B&I Testing performs an Ocala blower door test that fails, we identify the major leak locations on the same visit using smoke pencils and pressure differential probing. The builder’s team then has a target list to address. After repairs, we re-test (usually scheduled within 24-48 hours).
The re-test fee is typically lower than the initial test because the house is already set up. Most homes pass on the second test.
If you need a blower door test for an Ocala project, or you want a pre-drywall test to catch issues early, call (352) 756-2986, email brandon@banditesting.com, or reach us through the contact form.
Frequently Asked Questions
My home tested at 5.5 ACH50. How hard is it to get to 5.0? Usually 30–60 minutes of sealing. The leaks adding up to that 0.5 ACH50 over limit are typically 2-3 missed penetrations.
What’s the biggest single source of leakage in Florida new construction? It varies. Most commonly: bath fan ducts terminating in the attic, followed by recessed can lights, followed by attic access hatches.
Can I seal everything from the attic side after drywall is installed? Some leaks, yes. Plumbing stacks, line set penetrations, and bath fan duct connections can all be sealed from the attic. Top plate gaps and electrical penetrations are harder once the wall is closed.
Does spray foam insulation guarantee a passing test? Closed-cell spray foam in the attic creates a much better air barrier than fiberglass batts, but it doesn’t automatically guarantee passing. Penetrations still need to be sealed, top plates still need to be gasketed, and access hatches still need weatherstripping.
Talk to Brandon directly.
Residential energy testing in Marion County, FL.