How to insulate a garage flat roof
The majority of garages here in the UK will have some variant of flat roof. In reality, the roof will never be truly flat but will have a slight angle (typically below 15 degrees), this allows water to drain off.
When you are insulating a flat roof you have the choice to install it above the roof deck (a warm roof construction) or below the deck (a cold roof construction). The advantage of a warm roof construction is that you retain the full floor to ceiling height within the garage. It also means the deck construction stays warm (hence the name). This removes the risk of condensation forming on the cooler deck surface. If you’re opting for a cold roof construction then you’ll need to ensure there is an airgap between the insulation layer and the roof deck which will allow any moisture to be ventilated out through the eaves.
When adopting a warm-roof approach, start by cleaning and inspecting the existing roof deck for any signs of damage – these will need to be addressed before you can do anything. If it is not fully watertight then you will need to fit a vapour control layer down first (above the existing surface) before starting on the insulation. EcoTherm Eco-Torch boards
can then be laid. They should be loosely butted in a break-bond pattern and bonded to the surface using a PU adhesive. Strips should be fitted vertically around the perimeter to create an upstand of at least 25 mm. The chosen waterproofing layer can then be applied following manufacturer instructions. Take care to ensure the existing fall (pitch of the roof) is maintained and that any drains and gutters are adjusted as necessary.
If you opt for a cold roof construction then it is a good idea to first screw 50 x 50 mm battens into the side of the rafters beneath the roof deck. By fitting the insulation below this you can ensure that the minimum air gap (50 mm) is maintained. A void should also be left behind the fascias so that air can freely circulate through the construction.
Next, measure and cut EcoTherm Eco-Versal
boards to size to fit between the rafters using a sharp toothed saw. Be sure to carefully measure the gap between each rafter to ensure a tight fit as these may vary. The insulation should sit flush with the edge of the rafter with a stop battens side nailed below. Eco-Liner boards can then be fixed below the rafters with dry-wall screws at 125 mm centres and finished with a skim