The insulation can be adhered mechanically fixed or loose laid.
Minimum thickness warm roof insulation.
A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck.
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.
Ventilation is required for these roofs.
Building regulations and standards set the levels of thermal insulation required when carrying out building work.
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.
The vapour control layer is above the decking but below the insulation.
If you do have existing roof insulation the first thing to do is to check the depth if there is only 25mm of insulating material then this is likely to date back to the 1970s as this type of.
The insulation is immediately below the waterproofing layer.
With a warm roof the usual process is to split the insulation into two layers.
Warm flat roofs do not need to be ventilated as the insulation is above the structure.
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.