leafsta Posted November 10, 2023 Share Posted November 10, 2023 Currently building an extension on my house as a permitted development but i'm a bit out of touch with roofing membranes and the amount of airgap required when insulating between and below the rafters.. from my understanding it's a minimum of 50mm above the insulation so i'm guessing that means on a 175x50 roof, I can use no more than 125 PIR between the rafters... can anyone confirm if thats correct? Thanks in advance! Link to comment Share on other sites More sharing options...
Temp Posted November 10, 2023 Share Posted November 10, 2023 Yes that's correct. The membrane should drape/sag about 25mm between rafters leaving 25mm air gap. Should be ventilated at ridge and eaves. The drape is to stop water pooling above battens causing them to rot. Link to comment Share on other sites More sharing options...
Thorfun Posted November 10, 2023 Share Posted November 10, 2023 You can batten and counter batten above as well to give the air gap above when using breathable roofing membranes. Before doing so check with the manufacturer and building control. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now