Roofing insulation in single storey extension with pitched roof Information, help and tips on many areas of roofing including trusses, tiling, venting, insulation etc....

[Dannyboy7]

I have a small single storey extension at the back of my house with a pitched roof, the house is a Victorian terrace and the extension also looks pretty old .

The extension is off the kitchen and has suffered from condensation in past, so I've stripped away all the old plaster, have ventilated and will fit a radiator.

When I've removed the plasterboard ceiling there was no insulation between the ceiling and the roof tiles and the underlay is thick polythene (looks like visqueen) so not breathable.

I want to insulate between the rafters before I fit a new ceiling, but am concerned that the insulation should be breathable, because of the visqueen.

Any advice on suitable insulation products to use?

[stoneyboy]

Hi dannyboy7,
Unless you are going to replace the non breathable underslaters felt with a breathable one you will have to leave a ventilated gap. If you have facials and soffits the easiest way is to fit soffit vents both sides of the roof. Alternatively you could fit strip vents on the top of the facias but it's a lot more work.
Once you have done this you can insulate between the rafters leaving a 25mm gap above the insulation, sheets of pier insulation work well. You will need to fit a continuous vapour barrier before you cover the inside of the roof.
Regards S