Roof Insulation

Rigid insulation boards for warm flat roofs and pitched roof construction. On a warm roof the insulation sits above the deck and below the waterproofing, which keeps the structural timbers on the warm side of the insulation and largely removes the condensation risk that comes with older cold-roof build-ups.

A typical warm flat roof build-up

From the inside out: structural deck, vapour control layer, rigid insulation board, then the waterproofing membrane bonded over the top. Getting the vapour control layer continuous and sealed matters as much as the insulation itself — gaps let warm moist air reach the cold side of the boards.

How much do you need?

Board thickness is driven by the U-value you are working to and how much height you have at the abutments, door thresholds and upstands. Measure the available upstand height first: it is the constraint that most often decides the specification on a domestic extension or garden room.

Insulating under an EPDM roof? Use our roof kit calculator to size the membrane, and see EPDM termination bars for finishing upstands against a wall. Where a build-up needs to breathe, an EPDM flat roof breather vent lets trapped moisture out. Full systems are in our EPDM roof kits.