Spray Foam Roofing: What to Know About Open Cell Foam

Open cell spray foam is lightweight, flexible, and highly breathable—but it’s rarely used for exposed roofing. So why does it come up in roofing conversations?

Let’s break down how open cell foam compares to closed cell, when it’s appropriate, and why most Georgia homes and commercial roofs should use closed cell foam instead.

What Is Open Cell Spray Foam?

Open cell foam is a type of polyurethane insulation with a spongy, semi-rigid structure. The “open” cells allow air and vapor to pass through, making it breathable and lightweight.

Key Properties:

• Lower density (~0.5 lb/ft³)

• R-value of ~3.5 per inch

• Expands up to 100x its original volume

• Softer and more flexible than closed cell foam

Where Open Cell Foam Is Used

Open cell spray foam is ideal for:

• Interior attic insulation

• Wall cavities in homes and buildings

• Soundproofing applications

• Under-roof deck spray, beneath the roofing material (not exposed)

It’s popular in residential roofing systems where the goal is energy efficiency inside—not exterior waterproofing.

Why Open Cell Foam Is Not Used for Roof Surfaces

Open cell foam should not be exposed to the elements. Here’s why:

🚫 Not Waterproof
Open cell foam absorbs moisture, which leads to rot, mold, and breakdown if used on exterior roof decks.

🚫 Low Structural Strength
It lacks the compressive strength to support foot traffic or rooftop equipment.

🚫 Not UV Resistant
It must be fully sealed and protected—making it unsuitable for flat or low-slope roofing systems without an added cover.

🚫 Doesn’t Meet Roofing Standards
Closed cell foam meets IBC/IRC code for exterior roof systems. Open cell does not.

When Open Cell Foam Is Used with Roofing

There are limited cases where open cell foam may be applied to:

• Underside of metal roofs or roof decks

• Attic spaces with unvented assemblies

• Residential renovations seeking sound control

In these situations, open cell foam is sprayed under the roof deck—not on top of it—and must remain protected from moisture.

The Better Choice for Most Roofs: Closed Cell Foam

For all flat roofs, metal roofing retrofits, and spray-applied roofing systems, closed cell foam is the standard.

It provides:

• Waterproofing

• Structural strength

• High R-value

• Wind uplift resistance

• Compatibility with silicone or acrylic coatings

FAQ: Open Cell vs Closed Cell for Roofing

Can I use open cell foam as a roof system?
Not directly. It’s not waterproof or durable enough for rooftop use.

Is open cell foam cheaper?
Yes—but only for interior use. It fails quickly if used as a weather-exposed roofing system.

What foam should I use for roof repairs or replacement?
Closed cell spray polyurethane foam—especially in Georgia’s hot, storm-prone climate.

Get Expert Foam Roofing Advice from Roof Nuts

At Roof Nuts GA Roofing, we specialize in:

• Spray foam roofing (closed cell)

• Residential and commercial roofing

• Flat and low-slope roof systems

• Roof repairs, roof replacement, and recoating

We serve Atlanta, Augusta, Macon, Columbus, and surrounding areas. If you're not sure what type of foam your project needs—we’ll guide you.

📞 Call 404-476-6851
🌐 Visit RoofNutsGA.com