Flood-Tested, FEMA-Rated: Why Closed-Cell Should Be Your Default

It’s time to stop treating closed-cell like a “nice to have” and start treating it like a non-negotiable in flood-prone assemblies.

Floods don’t check zip codes.

They don’t care about remodeling budgets, slab elevations, or whether your last job got a five-star review. All it takes is one clogged culvert during a spring thaw… and suddenly the crawlspace you sprayed last October is swimming in stormwater.

And that’s when most insulation products wave the white flag.

Because flood damage isn’t just about water — it’s about what the water does to what’s in the walls. And if you’re still bidding fiberglass or cellulose anywhere near flood-prone zones, it’s time to rethink the playbook.

Why Most Insulation Dies in a Flood

Floodwater is dirty. It’s pressurized. It lingers. And it doesn’t care what material you installed.

• Fiberglass batts collapse like soggy pillows. Once soaked, they lose their shape, R-value, and airflow — and they stay wet. They trap bacteria, mold, and whatever floated in with the storm.

• Cellulose turns to sludge. It soaks like newspaper, and holds moisture like a sponge. By the time you smell it, you’re already dealing with spores.

• Open-cell spray foam, while great in the right applications, doesn’t stand a chance here. Its vapor-open nature — a plus in dry assemblies — becomes a liability. Water gets in, but it doesn’t get out.

These materials don’t just get wet. They stay wet. And once that happens, they’re not just ruined — they’re a health risk. Which means your client ends up paying twice: once to install, and again to rip it all out.

Closed-Cell Foam: The One That Sticks Around

Closed-cell spray polyurethane foam (ccSPF) isn’t like the others. When applied properly, it’s:

• Dense and rigid — no collapse or compression.

• Non-absorbent — water can’t wick in.

• Adhesive — it stays stuck to studs, block, or concrete.

• Vapor-resistant — at 1.5–2” thickness or more, it acts as its own vapor barrier.

So when floodwaters come through, the drywall might be trashed, the flooring might be ruined — but the foam is still there.

Still intact. Still performing. Still saving your client from a total rebuild.

FEMA’s Classification: This Isn’t Just Marketing

In FEMA Technical Bulletin 2, insulation materials are ranked based on how well they handle floodwater. Only Class 4 and Class 5 materials are allowed below the Base Flood Elevation.

• Fiberglass? Doesn’t make the list.

• Cellulose? Not even considered.

• Open-cell foam? Nowhere to be found.

• Closed-cell spray foam? Class 5 — the highest possible rating.

That rating isn’t hypothetical. It means that ccSPF can withstand direct, prolonged contact with floodwater and still be considered usable — assuming proper prep and stable substrates.

That’s why FEMA wants it in crawlspaces, basements, and the lower four feet of coastal homes. And if you’re bidding those jobs? You should want it too.

So What Happens If It Gets Wet?

Here’s where theory meets field reality.

After a flood, it’s common to walk into a building where everything looks wrecked — drywall, baseboards, flooring. But behind it all? The foam is still firm, stuck, and unsoaked.

Yes, there might be some discoloration. There might be a faint odor during drying, especially if the water sat too long or was full of contaminants. But in most cases, the foam doesn’t have to come out.

If it was sprayed onto stable substrates like:

• Concrete

• CMU block

• Brick

• Pressure-treated wood

… and that surface hasn’t rotted or shifted, the foam can usually be dried, wiped, and treated with a light antimicrobial if needed — and then left in place.

But Can You Always Save It? Not Quite.

There are limits — and knowing them is key.

• If the foam delaminates (peels off the wall), it’s compromised.

• If the substrate behind the foam is rotting or unstable, the adhesion’s worthless.

• If you sprayed over wet wood to begin with? Mold may have bloomed behind the foam — and now you’re in teardown territory.

• If the flood was blackwater (like from a hurricane surge or sewer backup), the damage call becomes more complex. You'll want documentation.

Bottom line? Closed-cell gives you the option. It doesn’t guarantee survival — but it often earns it. And no other insulation type can say that.

Real-World Evidence: The Foam That Didn’t Quit

After Hurricane Katrina, building scientists surveyed flooded homes in New Orleans. Most were total losses — but in a few homes with ccSPF, the lower wall cavities told a different story.

The foam hadn’t moved. It hadn’t soaked. In many cases, it passed reinspection and was left in place.

Same thing after Harvey in Texas. After Ida in Louisiana. Ask any contractor who’s sprayed ccSPF in a flood zone and then been called back. They’ll tell you the same thing:

“The foam made it.”

Why Contractors Need to Start Talking About This

Here’s what’s wild: FEMA’s been publishing this info for years. And still, most builders in flood zones are quoting fiberglass like nothing’s changed.

That’s not just a bad spec — it’s a missed opportunity.

When you quote closed-cell foam in a flood-prone project, you’re not just selling insulation. You’re selling resilience. You’re giving your client one less thing to replace next storm season.

And most of your competitors? Aren’t even mentioning it.

Closed-Cell as Flood Strategy — Not Just a Spec Line

It’s time to stop treating closed-cell like a “nice to have” and start treating it like a non-negotiable in flood-prone assemblies.

If GFCI outlets are code near water, and pressure-treated lumber is required on sill plates — why are we still stuffing cotton candy into crawlspaces?

Foam contractors are in the perfect position to lead this conversation. Not just because you install it — but because you understand it.

No batt guy is quoting FEMA ratings. No cellulose crew is talking Class 5 flood approval.

But you can.

Final Word: Spray Foam That Doesn’t Fold When the Flood Hits

Closed-cell spray foam isn’t just insulation. It’s damage control. It’s code-compliant. It’s field-tested. It’s a reason to pick your bid over the next guy’s.

So next time you’re estimating a crawlspace near the river… or a basement below grade… or a wall system that lives in the splash zone — don’t just talk R-value.

Talk FEMA. Talk Class 5. Talk about the day after the flood.

Because when the water rises, the batt guys will be tearing out soggy insulation.

You’ll be the one who built it to last.

by Gage Jaeger, Owner and Founder of Foambid