Minimum Thickness Warm Roof Insulation

Cold deck this is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof.

Minimum thickness warm roof insulation. If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters. Warm flat roofs do not need to be ventilated as the insulation is above the structure. A warm flat roof or a built up roof bur is one where all the insulation is above the joists deck making them part of the warm fabric of the building. Cold flat roofs are typically avoided as you d need to install ventilation which can prove problematic for many reasons relating to space labour costs etc.

A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck. Ventilation is required for these roofs. With a warm roof the usual process is to split the insulation into two layers. The vapour control layer is above the decking but below the insulation.

The insulation is immediately below the waterproofing layer. Building regulations and standards set the levels of thermal insulation required when carrying out building work. Column a is for extensions where the existing dwelling s walls and roof u values are worse than 0 70 w m k in the walls and worse than 0 25 w m k in the ceiling.