The Dangers of Installing Spray Foam Over Wet Insulation

Installing spray foam over wet insulation is one of the most serious and costly mistakes in commercial roofing. Here's exactly what happens and why it's absolutely non-negotiable to remove wet insulation first.

What Happens Physically

When foam is applied over wet insulation, the moisture beneath the membrane heats up during the foam's exothermic reaction and converts to steam. This steam has nowhere to go and creates pressure pockets — blisters — beneath and within the foam. These blisters compromise adhesion, create weak spots in the waterproofing layer, and can rupture over time, leaving exposed areas.

The Performance Consequences

Foam applied over wet insulation: doesn't adhere properly to the substrate in wet areas, develops blisters that can grow and rupture over time, fails to achieve uniform R-value across the roof, allows continued moisture movement beneath the new system, and can actually accelerate insulation degradation by trapping moisture that can't escape.

Why Some Contractors Skip This Step

Wet insulation removal adds cost and time. Core sampling costs money. Some contractors skip these steps to win the bid with a lower price — knowingly or unknowingly setting up a system for failure. The building owner pays for this shortcut when the roof fails prematurely.

The Non-Negotiable Standard

Core samples before any restoration. All wet insulation removed and replaced before foam application. Third-party inspection to verify. Any contractor who doesn't follow this standard should not be hired for spray foam roofing.