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Is it worth insulating between the rafters?

Discussion in 'Building' started by indus, 19 Oct 2013.

  1. indus

    indus

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    Hi

    I'm having a two storey extension built at the moment. It has a pitched roof.

    There will of course be insulation in between the ceiling joists but is there anything to be gained but adding celotex between the rafters?

    It's an Edwardian house and so on the whole not great for thermal efficiency and I'm keen to take any opportunity to improve it. However insulating between the rafters was not included in my builders quote and so I will have to pay extra. Obviously I only want to foot the additional cost if there would be a benefit.

    Many thanks for your help
     
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  3. limerockconstruction

    limerockconstruction

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    Depends on if you are using the loft. If you will be storing stuff up there it might be worth considering tri-Iso or equivalent for the rafters, but if not you would be better off just throwing another layer of quilt up there. Much more cost effective.
     
  4. tony1851

    tony1851

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    +1 definitely
     
  5. indus

    indus

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    Sorry guys, I'm a bit unclear.

    The loft space will never be converted to living space but I do intend to use it for storage.

    I've read mixed reviews about tri iso.

    So would there be anything to be gained by insulating between the rafters or as LRC says should I just throw an extra layer of rockwool between the joists?

    Many thanks
     
  6. noseall

    noseall

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    The loft space above the blanket of ceiling insulation is meant to be cold and drafty. It keeps the roof healthy.
     
  7. phatboy

    phatboy

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    The new roof trusses in the extension should be able to accommodate 300mm of insulation which meets the current standards.

    You could go further, and fix timber at 90 degrees to these, and add more insulation between then, then floor over the top.

    Insulating the rafters is pointless, your loft will have a breeze flowing through it from the soffit boards, so the loft will never be warm
     
  8. indus

    indus

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    Thanks, point taken on the ventilation required through the loft space.

    But then what happens when you do a loft conversion? Then the loft space becomes habitable and heated and the health of the roof timbers is still maintained isn't it?

    My own loft conversion has a breathable membrane to allow this.

    So why can't I keep my uninhabitable loft space warm in a similar way?

    Many thanks
     
  9. stuart45

    stuart45

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    When the roof space is habitable it's heated so it's less likely to have condensation problems. If you insulate at the ceiling joists you need an air flow because the loft becomes much colder and moisture can attack the timbers. Insulating at the rafters as well is pointless as the heat is lost with the aair flow.
     
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  11. indus

    indus

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    Thanks, I understand what you all mean now :)

    One of the reasons I wanted to keep the loft space 'warm' was because I wanted to have a loft hatch from my master bedroom into this space. I'm worried that a loft hatch will then let cold air into my bedroom.

    Thanks again
     
  12. phatboy

    phatboy

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    Put a piece of thick Kingspan on the back of the hatch and it won't loose any significant amount of heat
     
  13. indus

    indus

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    That's a good idea, thanks! :)
     
  14. phatboy

    phatboy

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    I foun out recently, it can be bought in small pieces, so you dont have to buy an 8" x 4" sheet, they do ones that will roughly fit a hatch for about £12 in the thicker sizes
     
  15. stuart45

    stuart45

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    Do you need insulation in Jersey? :D
     
  16. phatboy

    phatboy

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    Everyone asks this! I guess the answer is 'less so than you'! Worst temperature I remember here is -1c, and that was the winter just gone. It generally stays above 0 though!
     
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