Insulation between roof joists.

Discussion in 'Builders' Talk' started by smithybora, Jan 26, 2012.

  1. smithybora

    smithybora New Member


    I am in the middle of building an extension. Its a lean too off the the existing house. Size is only 4mx4m. The internal ceiling is going to follow the pitch of the roof.

    I have used 6x2" joists. I just wanted to know. How thick the insualtion needs to the between the joists. Would 50mm be ok. That would leave plenty for an air gap.
    Or would either 75mm or 100mm be better.


  2. 100mm minimum wth 50mm air gap.
    You should have building regs which will specify all requirements.
  3. smithybora

    smithybora New Member

    Thanks for the quick reply. Just couldnt get hold of regs guy today wanted to pick it up first thing in the morning.

    Thanks. The 6" joists will work out nicley then.

    thanks again.

  4. sinewave

    sinewave Screwfix Select

    Stick as much as poss in whilst leaving the regulatory 50mm gap between the insul and the back of the felt.

    That'll be 100mm Cellotex then! 
  5. Ask your Bco, I think the latest requirement might be 125mm, but your drawing should tell you unless yur working on building notice in which I would ask the BCO what he wants anyway. If it is 125 you need to do 100mm between the joists leving 50mm airgap and 25mm on the underside

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