Raising your house gets your living space above the flood. It also leaves the underside of your floor open to Louisiana’s heat and humidity. A floor that sat on a slab or a low crawl space is suddenly 6, 8 or 10 feet in the air, with wind, rain and muggy air moving across it all year.
That’s why so many Slidell and St. Tammany homeowners pair house raising with spray foam insulation under the floor. Here’s what you need to know to do it right.
Why insulate under a raised house
- Comfort and energy bills. An uninsulated floor over open air makes rooms cold in winter and lets heat soak in during summer. Your A/C works harder and the floors feel it.
- Humidity and moisture. Warm, wet Gulf Coast air reaching the cool underside of an air-conditioned floor can condense. Over time that means cupped wood floors, musty smells and mold on the subfloor.
- Pipes and ducts. Plumbing and ductwork rerouted under a newly raised home are exposed. Insulating the floor system helps protect pipes in hard freezes and keeps ducts from sweating.
- Pests and wind. A sealed floor blocks drafts, insects and rodents from coming up through gaps around pipes and wires.
Why closed-cell spray foam is the usual choice
Under a raised house, insulation lives in a tough spot: open air, humidity, wind and possibly floodwater. Closed-cell spray foam handles that better than the alternatives.
| Insulation under a raised floor | How it holds up |
|---|---|
| Closed-cell spray foam | Resists water, works as a vapor retarder at typical thicknesses, adds stiffness, and seals air gaps around pipes and wires |
| Open-cell spray foam | Absorbs water and lets humid air through. Not recommended under floors open to outdoor air |
| Fiberglass batts | Sag, hold moisture and fall out over time. Often torn out after a few years |
| Rigid foam board | Can work, but seams and cut edges leave gaps for air and moisture unless carefully sealed |
Flood zone note: FEMA’s Technical Bulletin 2 rates sprayed polyurethane foam and closed-cell plastic foams as acceptable flood damage-resistant materials. Fiberglass, cellulose and open-cell foam are rated unacceptable. In a flood zone, materials below the required elevation must be flood damage-resistant, so closed-cell foam is the safer choice. Your engineer and permit office have the final word on what’s allowed under your home.
For a deeper comparison, see this guide to open-cell vs. closed-cell spray foam for Louisiana homes.
When to spray foam during a house raising project
Timing matters. Spray too early and the foam gets damaged or has to be cut out for plumbing and wiring. Wait too long and skirting or storage walls block access.
- The house is lifted on steel beams and cribbing.
- The new foundation is built and the house is set at its new height.
- Plumbing, electrical and ductwork are reconnected under the floor and pass inspection.
- Any rotten sills, joists or subfloor are repaired. Fix framing before it disappears behind foam.
- Spray foam goes on the underside of the subfloor, between the floor joists.
- Skirting, lattice, breakaway walls or storage are finished last.
Tell your house raising contractor early that you plan to insulate, so the schedule leaves room for the spray foam crew. See how long it takes to raise a house for the full timeline.
What to check before the foam goes on
- Dry framing. Wood should be dry before it’s sealed in. Installers typically check moisture content, especially after a wet spell or if the house flooded before it was raised.
- Termite plan. Formosan termites are a real threat in southeast Louisiana. Foam doesn’t attract them, but it can hide damage. Talk to your termite company first and leave the inspection gaps they ask for. More on spray foam and Formosan termites in Louisiana.
- Access to pipes and wires. Ask the installer to keep cleanouts, valves and junction boxes reachable.
- Thickness and R-value. Closed-cell foam is commonly applied 1 to 3 inches thick under floors, depending on the R-value you want and your budget. Get the planned thickness in writing.
- Flood vents and openings. Spray foam goes on the floor system only. It should never block the flood openings required in an enclosed area below the home.
What it costs and who pays
Under-floor spray foam is priced by square footage and foam thickness, and access is usually easiest right after a raise. Get a quote from a spray foam installer while the house raising project is still being planned, so you can budget for both.
If your raise is funded by a FEMA grant (HMGP or FMA), remember that grants typically cover the elevation work itself. Upgrades like insulation are often the homeowner’s cost. Confirm with your grant administrator. See our FEMA elevation grants guide and house raising cost guide.
Questions to ask your spray foam installer
- Are you using closed-cell foam, and what thickness and R-value?
- Is the product suitable for a floor exposed to outdoor air?
- How will you protect pipes, wires and junction boxes?
- Have you coordinated with my termite company on inspection gaps?
- How long should we stay out of the house after spraying?
- Do you carry liability insurance, and can I see your license?
Get both jobs done right
Raising your home and insulating the floor are two jobs done by two different trades, and they go best when planned together.
- House raising in Slidell and St. Tammany: request a free estimate and a local house raising contractor will look at your home.
- Spray foam under your raised floor: see under-floor spray foam for raised homes or get an estimate for spray foam insulation in Slidell.
Source: FEMA Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (2025).
Common questions
What is the best insulation under a raised house in Louisiana?
Closed-cell spray foam is the most common choice under raised and elevated Louisiana homes. It resists water, acts as a vapor retarder at typical thicknesses, and FEMA rates closed-cell and sprayed polyurethane foam as flood damage-resistant. Fiberglass batts tend to sag, hold moisture and fall out under homes open to outdoor air.
When should I spray foam under my house during a house raising project?
After the house is set on its new foundation and plumbing, electrical and ductwork under the floor have been reconnected and inspected, but before skirting, lattice or storage walls close off the space underneath.
Does spray foam under the floor count as flood damage-resistant?
FEMA Technical Bulletin 2 rates sprayed polyurethane foam and closed-cell plastic foams as acceptable flood damage-resistant materials. Open-cell foam, fiberglass and cellulose are rated unacceptable. Follow the manufacturer's installation instructions and your local floodplain rules.
Will spray foam under my floor cause termite problems?
Foam doesn't attract termites, but it can hide their activity from inspectors. Talk to your termite company before installation, leave inspection gaps where they ask, and keep your termite contract active.
Is open-cell spray foam OK under a raised house?
Generally no. Open-cell foam absorbs water and lets humid air through, which is a poor fit for a floor exposed to outdoor air and possible flooding. Closed-cell foam is the standard recommendation under raised floors.