How to Insulate a Garage - Installing on Floors, Walls and Roofs

23 June 2020 EcoTherm Insulation

This is the final blog in our series on insulating garages. If you haven’t already seen them, it is a good idea to go back and read the previous blogs on preparing the space and the building regulation requirements to make sure you don’t miss any steps.

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How to insulate garage walls

Let’s assume you’re looking to insulate a 215 mm solid brick walled garage. First you need to fix 25 x 47 mm treated softwood battens into the wall at 600 mm centres. A damp proof course strip should be applied between the face of the batten and the wall to provide protection against any moisture penetration. You will also need to batten around any opening such as windows.

You can then simply fix EcoTherm Eco-Liner to the battens using drywall screws at 125 mm centres. These need to be driven so the heads sit just below the surface. As Eco-Liner combines PIR insulation and a 12.5 mm layer of plasterboard in a single board, you can simply apply a skim to the surface. Once dry, it will be ready to decorate.

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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

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How to insulate garage floors

In most cases, the garage floor will be a solid concrete slab. To insulate this, you may need to create a step-up from other internal spaces (assuming the existing floor height is the same as those in the rest of the house). If you choose to retain the slab then a damp proof membrane should first be laid. The only alternative is to dig the slab out which can be fairly costly and time consuming.

The installation process is then fairly straight forward. Eco-Versal boards should be cut to size and loose laid with 20 mm upstands around the perimeter. A separation layer is then placed above this followed by the floor screed.