Crawl Space Insulation & Encapsulation, Lehi, UT

Two approaches

Vented crawl space or sealed crawl space

Utah's energy code allows both. They put the insulation in different places, and they behave differently in a Utah County winter.

Factor	Vented crawl space	Sealed (unvented) crawl space
Where the insulation goes	In the floor above, between the joists. Code R-30.	On the foundation walls. Code R-15 continuous or R-19 cavity.
Foundation vents	Open year round	Closed and sealed
Ground	Bare or a loose vapor barrier	Continuous vapor barrier, sealed at the walls and seams
Ducts and plumbing under the floor	Outside the conditioned space. Ducts lose heat, pipes can freeze in a hard cold snap.	Inside the envelope. Ducts stay warm, pipes stay above freezing.
Rim joist	Sealed and insulated either way	Sealed and insulated either way
Floor comfort	Better than nothing, but air still moves under the floor	Floors run close to room temperature
Moisture	Vents bring in humid summer air that condenses on cold ducts and pipes	Controlled. Needs a vapor barrier and, where there is a moisture source, a dehumidifier or conditioned air supply
Best fit	Dry crawl spaces with no mechanicals below the floor, or where sealing the vents is not practical	Most Lehi homes with ducts or plumbing in the crawl space

Code values: Insulation Institute, Utah energy code summary (2025), Climate Zone 5: floors R-30, crawl space walls R-19 or R-15 continuous. Last checked September 30, 2026.

Moisture first

What has to be true before insulation goes in

Insulating a damp crawl space is how you turn a moisture problem into a mold and rot problem. So we look for water before we talk about R-values.

Utah County is dry, but crawl spaces are not immune. On the bench, spring snowmelt runs through the soil. In the flatter parts of Lehi and out toward Saratoga Springs, the water table and irrigation overspray are the usual culprits. Add a few decades of a bath fan venting under the house or a slow plumbing leak and you get the musty smell people call about.

During the inspection we check for standing water, staining on the foundation walls and sill plate, dark or soft framing, efflorescence on the concrete, and condensation on ducts and pipes. If there is a water source, grading, drainage, or a sump has to happen first, and that is a different trade. We will say so plainly rather than insulate over it.

Vapor barrier and encapsulation

A ground vapor barrier, heavy polyethylene laid over the dirt and run up the walls, is cheap and goes under every sealed crawl space we insulate. Full encapsulation, with taped seams, the barrier sealed to the foundation, and a dehumidifier or a conditioned air supply, is a bigger job that only pays off where moisture is a real, ongoing problem. Ask us about it during the inspection and we will tell you whether your crawl space needs it or just needs the basics.

Narrow crawl space walkway lit from the far end — The first visit is a crawl with a light and a moisture meter, not a quote from the hatch. Stock photo.

What we do down there

Crawl space insulation services in Lehi

Foundation wall insulation

For sealed crawl spaces. Rigid foam board or closed-cell spray foam on the concrete to R-15 continuous, the path that rejects moisture and needs no framing.

Floor insulation

For vented crawl spaces. Batts fitted tight to the subfloor in every joist bay and supported so they stay there, to R-30. Falling batts are the most common thing we find in older Lehi crawl spaces.

Rim joist and sill plate

The band where the foundation meets the floor framing. Sealed and insulated on every job, usually with closed-cell foam. The same detail as on our basement insulation work.

Ground vapor barrier

Heavy polyethylene over the dirt, lapped and run up the walls, under every sealed crawl space. Stops ground moisture from evaporating into the house.

Vent sealing

Foundation vents closed and sealed when converting to a sealed crawl space, so the insulation on the walls is not undone by open air leaks.

Cold-floor diagnosis

Sometimes the cold floor is the rim joist, sometimes a missing bay of insulation, sometimes a duct that fell apart. We find which before quoting.

How it works

The crawl space job, start to finish

01

Free inspection

We crawl it. Moisture, framing condition, existing insulation, ducts and plumbing, vent locations. Photos of everything. About 30–45 minutes.

02

Written scope and price

Vented or sealed, what goes where, vapor barrier, rim joist, and any rebate you qualify for. Flat, in writing.

03

Install

Debris cleared, vapor barrier laid, walls or floor insulated to the code path in your quote, rim joist sealed, vents handled.

04

Walkthrough

Photos of the finished work and the documentation a rebate application asks for.

Around Lehi

Which Lehi homes have crawl spaces

Most newer Lehi homes have full basements. Crawl spaces show up in three places: older homes in the original grid, additions, and split-level and rambler plans from the 1970s through the 1990s.

The older homes near Main Street and Center Street often have a shallow crawl space under part of the house and a cellar under the rest. These are the dirt-floor, vented, no-insulation crawl spaces that make the kitchen floor feel like a skating rink in January. Additions on older homes are usually built on a crawl space too, and the junction between the old foundation and the addition is a reliable air leak.

Split-levels and ramblers from the 1970s to 1990s, common in the tracts north of the freeway and in neighboring American Fork and Pleasant Grove, often have a crawl space under one wing with batts that were stapled up 30 years ago and have since fallen into the dirt. Putting them back is not the fix. Fitting new insulation properly and sealing the rim joist is.

Rebates on crawl space work

ThermWise floor insulation$0.20 per square foot in increments of R-19 or higher. Enbridge Gas customers, through a ThermWise authorized contractor. Applies to floor insulation in a vented crawl space.

ThermWise wall insulation$0.30 per square foot in increments of R-11 or higher. May apply to crawl space wall insulation in a sealed crawl space. Confirm with Enbridge before the job.

Wattsmart floor insulation$0.65 per square foot in electrically heated homes, $0.10 in electrically cooled homes, from R-11 or less to R-30. Rocky Mountain Power customers only, not Lehi City Power. Homes under 10 years old excluded.

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

Common questions

Crawl space insulation in Lehi, UT: FAQs

Should I insulate the crawl space floor or the walls?

It depends on whether the crawl space is vented or sealed. A vented crawl space gets insulation in the floor above it, R-30 under Utah's code. A sealed crawl space gets insulation on the foundation walls, R-15 continuous or R-19 cavity, and the floor is left open so the space is treated as part of the house. Sealed usually performs better in Utah County because the ducts and plumbing under the floor stay inside the conditioned envelope.

Is encapsulation necessary in Utah's dry climate?

Less often than in humid states, but not never. Utah County crawl spaces still get ground moisture, spring runoff on the bench, irrigation overspray, and condensation on cold ductwork in summer. A ground vapor barrier is cheap insurance under any sealed crawl space. A full encapsulation with sealed seams and a dehumidifier is only worth it where there is a real moisture problem, and we say so after looking.

Why are my floors cold?

Because the air under them is cold. In a vented crawl space, outside air moves under the floor all winter. If the floor has no insulation, or the batts have fallen out of the joist bays, the subfloor runs close to outdoor temperature. The rim joist at the edge of the floor is usually the single worst spot.

Can you insulate a crawl space that has standing water?

No. Water first, insulation second. A crawl space that floods or holds water needs grading, drainage, or a sump before any insulation goes in. Insulating over a wet crawl space traps moisture against the framing. We will tell you that during the inspection and point you to the right trade.

Does crawl space insulation qualify for rebates?

For Enbridge Gas customers, ThermWise pays $0.20 per square foot on floor insulation added in increments of R-19 or higher, through a ThermWise authorized contractor. Wattsmart pays $0.65 or $0.10 per square foot on floor insulation for Rocky Mountain Power customers only, which excludes most of Lehi.

Crawl Space Insulation in Lehi, Utah

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