Spray Foam Roofing for Existing Roofs: A Beginner's Guide

If you're new to spray foam roofing and wondering if it's right for your building, this guide covers everything you need to know.

What Is Spray Foam Roofing?

Spray polyurethane foam (SPF) is a two-component liquid system that's sprayed onto an existing roof surface. The components react and expand into a rigid, closed-cell foam that bonds directly to the substrate. A protective silicone or acrylic topcoat is then applied to protect the foam from UV radiation.

Can It Go Over My Existing Roof?

In most cases, yes. Spray foam can be applied over TPO, EPDM, metal, gravel BUR (after gravel removal), and modified bitumen systems — without tearing off the existing roof. The requirement is that the existing substrate has less than 25% wet insulation and the membrane is in acceptable condition.

What Does It Do?

Spray foam simultaneously: creates a seamless waterproof surface (eliminating seams — the #1 cause of leaks), adds insulation (R-6.5 per inch), can correct slope and drainage issues, and comes with a 10–20-year renewable manufacturer's warranty.

How Much Does It Cost?

Typically $4–$8 per square foot for foam plus silicone topcoat, depending on thickness and roof conditions. This is significantly less than full roof replacement at $7–$14 per square foot.

How Long Does It Last?

With proper maintenance and periodic recoating, a spray foam roof can last indefinitely. West Roofing Systems has installations from 1979 still performing today.

What's the First Step?

A professional inspection with core samples to assess moisture levels and determine eligibility. Contact West Roofing Systems for an honest, no-pressure assessment.