Rafter insulation....

Discussion in 'Builders' Talk' started by Ant62, Feb 14, 2019.

  1. Ant62

    Ant62 New Member

    I have a query regarding rafter insulation and condensation..

    14mths ago we had our hipped roof stripped and relaid with a permeable membrane underneath....

    Main issue.
    The rafters are 75mm deep.
    So im thinking of adding 25mm celotex in between the rafters and then putting T&G cladding over the to make it all look presentable and clean....
    Now because its an hipped roof we have 3 huge support beams which i intend to insulate up to and then cladd to the beams and then down the beams to the loft floor.....
    Behind the cladded area is an open area from where the beams are to the eaves where cool air comes in...
    So beacuse of the cool air coming in through the eaves and travelling up the 50mm gap in the rafters is the adequate enough to stop the condensation if any at all....
    Also the loft floor is well insulated under the floor.....

    Basically we want a clean n dry storage area....
  2. Ant62

    Ant62 New Member

    Managed to get hold of the roofer as he works away at times..

    He said that the membrane is permeable so it waterproof and breathable.....

    So im presuming that it is ok then to insulate.....!
  3. b4xtr

    b4xtr Active Member

    If you just want a dry storage area, just attach a breathable membrane to the underside of rafters
  4. Jitender

    Jitender Well-Known Member

    50mm celotex would offer much more benefits than 25mm

    In order for this you can add a 25 x 38/50mm batten to the roof rafters so that you retain the 50mm air flow.

    Did the roofer use a dry ridge/hip system or mortar the ridge tiles?
  5. Ant62

    Ant62 New Member

    Bedded the ridge tiles on mortar.......

    Is there a difference
  6. b4xtr

    b4xtr Active Member

    less air flow
  7. Jitender

    Jitender Well-Known Member

    In my loft conversion, the storage area behind the dwarf walls I just stapled superquilt to the underside of rafters, as cutting celotex was very difficult and awkward to get to.

    I replaced the soffits and fascias at the same time and used vented soffits which allowed ventilation.
  8. Ant62

    Ant62 New Member

    Ah right.....

    So am i ok then then to add an ridgid insulation then clad over.....!

    I will measure the rafters width tomoz and see what it costs to add extra depth..

    But will i get any condensation though....
  9. Jitender

    Jitender Well-Known Member

    As long as you leave 50mm air gap and have ventilation It will be fine. The foil on the boards acts as a vapor barrier, obviously it wont be a continuous one as joist in the way. Any joins in the rafters can be tape using aluminum foil. Make sure that insulation isn't blocking the eaves area.

    Remember installing the insulation a few years back in the middle of summer and I could feel the heat on the roof coming through, and the sheets do help keep the loft cooler in the warmer months, which would be umberable to get into.

    if your roof has the height than you could install ceiling collars to create a ceiling, which would help more with through ventilation, as well as giving you a void to install any cables etc.

    I had a flyer dropped through the other day and there are some companies offering 'seconds' on insulation board i.e minor cosmetic damage but haven't used these as prices have rocketed since doing my project.
  10. Ant62

    Ant62 New Member

    Im dont intend to insulate all the way the eaves...
    My plan is to insulate to the roof supports as its a hipped roof...

    If i can add photos to give an idea i will do so tomorrow..

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