Attic Air Sealing, Air Sealing Contractor, Lehi, UT

The physics

Why the attic floor is where Lehi houses leak

Heated air rises and pushes out through the ceiling. Cold air gets pulled in low to replace it. That loop is the stack effect, and it runs harder the colder the night gets.

Utah County winter nights sit in the teens and single digits. Inside, the furnace keeps the house at 68. That temperature difference is the engine. Warm air finds every gap in the ceiling plane and leaves through the attic. Every cubic foot that leaves gets replaced by a cubic foot of cold air drawn in through the rim joist, the crawl space, the garage wall, and the gaps around pipes and wires at the bottom of the house.

Insulation does not stop this. Blown fiberglass and cellulose slow heat moving through them, but air moves through and around them easily. Sixteen inches of insulation over a leaking attic floor still leaks, it just leaks a slightly longer path. That is why we seal before we blow, every time, and why a house that is already at R-49 can still be drafty and still get ice dams.

The attic floor is the right place to attack it because it is the top of the loop, it is accessible, and the leaks are concentrated in a few predictable spots.

Installer working across an attic floor before insulation is added — Sealing is hands-and-knees work across the whole attic floor, done before the blowing hose comes out. Stock photo.

Where the leaks are

The spots we seal on a Lehi attic floor

The same handful of details leak in nearly every house. The material changes by spot: sealant, foam, rigid board, or fire-rated products near heat.

Top plates. The joint where the drywall meets the top of every interior and exterior wall. Dozens of linear feet of small gap, and the biggest total leak in most attics. Sealed with foam or sealant along the full length.
Recessed can lights. Older non-IC cans are open to the attic and cannot be covered with insulation. They get an airtight, fire-rated cover box. Newer IC-rated airtight cans get sealed at the trim ring.
Plumbing and wiring chases. The vertical openings where drain stacks and wire bundles pass up through the framing. Often several square inches of open hole straight into the house. Blocked with rigid material and sealed.
Flues and chimneys. Clearance gaps around furnace and water heater flues and masonry chimneys. Sealed with sheet metal and fire-rated sealant only. Never foam.
Bath fan and range hood housings. Sealed at the ceiling and, where a fan has been dumping moist air into the attic for years, re-ducted outside.
The attic hatch or pull-down stair. Usually the single largest hole in the ceiling. Weatherstripped, and covered with a rigid insulated box or an insulated hatch cover.
Knee walls and dropped ceilings. In split-levels and bonus rooms, open framing cavities that connect living space directly to the attic. Blocked and sealed at the top.
Duct boots and HVAC penetrations. Supply and return boots sealed to the drywall, and attic duct joints sealed with mastic where they are accessible.

Sequence

Air sealing and insulation as one job

The attic floor is only bare once. Sealing it is cheapest and most thorough when the insulation is being added anyway, which is why it is included on every attic insulation job we run.

When an attic already has a thick layer, the crew moves the insulation aside at each leak point, seals it, and puts the insulation back. It is slower and the quote reflects that, but it is still the right fix for a drafty, well-insulated house. After an insulation removal, the floor is completely bare and the sealing is as thorough as it ever gets.

Rafter baffles at the eaves and insulation dams around the hatch are part of the same visit. Baffles keep the soffit vents open so the attic breathes correctly once it is sealed from below. Dams keep the insulation from spilling into the hatch opening.

Blower door testing

A blower door measures how leaky the whole house is before and after. It is useful on larger jobs and sometimes required by rebate specifications. Whether your job includes one depends on the scope and the current ThermWise specification, and we tell you when we quote.

ThermWise air sealing rebate

Single-family homes$200 per job plus $0.10 per square foot of conditioned floor area, up to a maximum of $850. Enbridge Gas customers. Must be done by a ThermWise authorized contractor and meet ThermWise air-sealing specifications.

Worked exampleA 2,400 square foot home: $200 + (2,400 × $0.10) = $440. A 6,500 square foot home hits the $850 cap. General guidance only, confirm the current amount with Enbridge.

WattsmartRocky Mountain Power's Utah insulation rebates cover attic, wall, and floor insulation. Air sealing is not listed as a separate measure on the Utah page as of our last check.

Amounts set by the utilities and subject to change. Source: Enbridge Gas ThermWise. Full guide and eligibility checker. Last checked September 30, 2026.

How it works

The air sealing job, start to finish

Free inspection

We walk the attic and map the leak points: top plates, cans, chases, flues, hatch. We note anything that needs a fire-rated detail or a re-ducted fan. About 30–45 minutes.

Written scope and price

Every leak point listed, the material for each, whether insulation is being added or moved aside, and the rebate you qualify for. Flat, in writing.

Seal

Walkways protected. Each detail sealed with the right product. Can light covers, chase blocking, flue collars, hatch cover installed. Baffles and dams set.

Walkthrough

Photos of every sealed detail, blower door numbers if tested, and the documentation a rebate application asks for.

Common questions

Attic air sealing in Lehi, UT: FAQs

Is air sealing worth it on its own?

Usually it is done together with attic insulation, because the attic floor is only accessible once and sealing it is cheapest while the insulation is being added anyway. On its own it is still worth it when the attic is already at R-49 but the house is drafty, or when ice dams keep forming on a well-insulated roof. Those are air leakage problems, not insulation depth problems.

Can a house be too tight?

Yes, in theory, and almost never in practice for an older Lehi home. Air sealing an attic floor closes the big leaks that let conditioned air escape; it does not make a 1985 house airtight. Where a job is large enough to change how the house breathes, we talk about mechanical ventilation before we start, not after.

Is a blower door test required for the ThermWise rebate?

ThermWise requires air sealing to be done by an authorized contractor and to meet its air-sealing specifications. Whether a test is part of that depends on the current program specification, which Enbridge sets and changes. Confirm with Enbridge before the job, and we will tell you what the specification calls for when we quote.

What is the stack effect?

Warm air rises. In winter, heated air pushes up through every gap in the ceiling into the attic, and cold outside air gets pulled in low through the rim joist, the crawl space, and gaps around the foundation to replace it. The taller the house and the colder the night, the stronger the pull. Sealing the top of the house, the attic floor, is the most effective place to interrupt it.

Will air sealing stop ice dams?

It is the main fix for them. Ice dams form when heat leaking into the attic melts snow on the roof, which refreezes at the cold eaves. Sealing the leaks and insulating to depth keeps the roof deck cold so the snow stays snow. Proper eave baffles and ventilation finish the job.

Attic Air Sealing in Lehi, Utah

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