EcoTherm roof insulation is not water-resistant. We recommend using additional materials to protect EcoTherm cavity wall insulation, roof insulation, and floor insulation from moisture.People who want to use EcoTherm products to insulate their floor should use a Damp Proof Membrane (DPM) to prevent water damage. Products that are laid against a concrete slab should be overlaid with a protective membrane. The membrane should have a minimum of 500 gauge.