How To Insulate An Old Slate Roof

Answered 14th jan 2013 like 2.

How to insulate an old slate roof.

If you want to insulate the sloping roof you definitely don t want to install spray foam against the back side of the slates. With a warm roof the usual process is to split the insulation into two layers. You would first have to create a vent channel under the slates by installing 1x1 sticks at the top of each rafter bay followed by stiff material like rigid foam or plywood. Equally the reverse is true.

With an assumed pre existing u value of 2 23w m the best options are as follows. Check the depth between your trusses and the slates then install the correct thickness of kingspan in the gaps allowing for a 25mm air gap between the kingspan and the slates. If you want to avoid internal changes you can do so by insulating externally. To insulate the roof itself you either use spray foam or retrofit with it with rigid foam board.

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 materials used to insulate under the roof include batts of mineral or glass wool insulation held in place by battens of wood attached to and across the rafters. An advantage of spray foam is it s quick whereas foam board needs to be cut and measured which can be a chore. U value 0 38w m.