Spray Foam Roofing vs Spray Foam Insulation: 4 Differences

Both are spray polyurethane foam, but roofing SPF and insulation SPF are different products designed for different applications. Here are the 4 key differences.

1. Density and Compressive Strength

Roofing SPF: 2.8–3.0 lb/cu ft density, 25–60 PSI compressive strength — designed to support foot traffic, equipment loads, and weather. Insulation SPF (interior walls/attics): 0.5–2.0 lb/cu ft density, lower compressive strength — designed for insulation performance in protected environments, not outdoor exposure.

2. UV Stability

Roofing SPF: formulated to maintain structural integrity during the brief window before topcoat is applied. Still degrades with extended UV exposure — hence the required topcoat. Interior insulation SPF: never exposed to UV — UV stability is not a design criterion.

3. Moisture Resistance

Roofing SPF (closed-cell): water-resistant, low water vapor permeance — serves as both insulation and vapor barrier. Interior open-cell SPF: absorbs moisture, high vapor permeance — not appropriate for exterior or roofing applications.

4. Application Requirements

Roofing SPF: requires professional plural-component spray equipment, manufacturer-approved applicators, third-party inspection, and topcoat application immediately after foam. Interior insulation SPF: simpler application, no topcoat required, different equipment specifications.

The Key Takeaway

Never allow interior insulation foam to be substituted for roofing-grade SPF. They are not interchangeable — interior foam applied to a roofing application will fail. Always verify that your contractor is using roofing-grade, manufacturer-approved materials.