Why You Should Never Install TPO Over Gravel Built-up Roof

When a gravel built-up roof (BUR) reaches end of life, the question becomes: what goes on top? TPO over gravel is sometimes proposed — but it's not standard practice and creates serious problems.

The Gravel Problem

Gravel BUR roofs have an uneven, jagged surface covered in loose stones. TPO is a sheet membrane that requires a smooth, flat substrate for proper adhesion and performance. Installing TPO directly over gravel results in: poor adhesion, potential punctures from sharp aggregate, uneven surface that creates stress points, and an installation that most TPO manufacturers will not warranty.

What Contractors Sometimes Do

Some contractors remove the gravel, then install a cover board over the existing BUR before laying TPO. This works but adds significant cost and labor — and still leaves you with a seamed membrane that will face the same aging issues as any TPO installation.

The Better Alternative: Spray Foam

Spray polyurethane foam is specifically designed for gravel BUR applications. After hydro-vacuuming the gravel, foam is applied directly to the existing BUR substrate — which, once gravel is removed, provides an ideal bonding surface. The foam fills in all irregularities, adds insulation, and creates a completely seamless waterproof membrane. This is the industry-preferred approach for gravel BUR restoration.