Retro-insulating a mansard roof

Discussion in 'Eco Talk' started by Will Mainwaring, Feb 1, 2017.

  1. Will Mainwaring

    Will Mainwaring New Member

    Hi there,
    Does anyone have any advice on how to retrospectively insulate a mansard roof please?
    Here's the house from the front:


    Here's a diagram of the house from the side:

    There's a lot of heat loss from where the roof comes down the sides.
    I've already lagged the loft, but cannot get access to the cavity between the roof and upstairs walls from the loft. The rafters poke out of the top of the ground floor, and this is boarded. I've read that it mustn't be pumped full of insulation due to needing air movement in the void, lack of which causes condensation.

    Thanks in advance for your help,
  2. wiggy

    wiggy Screwfix Select

    Insulate the inside walls?
  3. Will Mainwaring

    Will Mainwaring New Member

    Thanks for the reply. That was my first thought, but unfortunately we have fitted a bathroom with tiled wall against half of one side of the mansard roof, so I'd need to remove all the bathroom tiles that we've fitted to do this. There are sections of unobstructed wall elsewhere that I could cut out to gain access, but wanted to try and avoid this expensive measure if possible. It would be a last resort.
  4. KIAB

    KIAB Super Member

    One option I've seen done a lot, is to remove tiles on the sides, insulate between studs & fit new breathable membrane & rehang tiles.
    Orginal felt is probably well past it's best, & it's a easier than reboarding & redecorating inside.

    And don't even consider blown in insulation, or pumped expanded foam, had a friend who had it done, ended up blowing plasterboard off two walls & bringing down a ceiling.
    Last edited: Feb 1, 2017
  5. Will Mainwaring

    Will Mainwaring New Member

    Thanks KIAB, that was something that I was considering too. It might be easier to attack from the outside, and like you suggest, upgrade the innards at the same time. I'm guessing that I would need a roofer to do this job rather than any other trade?
  6. KIAB

    KIAB Super Member

    Yep a roofing firm, it's far less intrusive, no mess inside, so happy wife.:)

    But, there is a second option, you might be able to loose the siding hanging tiles, still insulate the inner wall with 75mm Kingspan & go with a rendered wall or block wall.
  7. Will Mainwaring

    Will Mainwaring New Member

    Thanks for this idea, I'd not considered it!
    And yes, happy wife = happy life...
  8. sospan

    sospan Screwfix Select

    You may be able to do something with spray foam which will coat the back of your bathroom wall. Not the cavity wall insulation but applied with a spray gun. You may be able to get away with a smaller opening.

    There are DIY kits available but would recommend you do it after the temperature rises as the canister is sensitive to cold
  9. Will Mainwaring

    Will Mainwaring New Member

    That's a good idea, thanks.

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