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Heating and cooling: Loft Insulation warm loft v cold loft

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    Having read much of the discussions - I get the general message... insulate then insulate before thinking too hard about heatingsystems (Tony esp!). I am engaging in a major refurb project on an old cottage in N yorks with thick stone walls and a very old pantiled roof. Stage 1 of the project is to renew / refurb the roof and get in as much insulation as possible. The challenge is though, to keep some of the very attractive old timbers (oak purlins etc) with a vaulted ceiling etc.

    I was proposing to go with 100mm or 125mm kinsgpan under the tiles / between rafters. But thinking about it, that means I am heating the loft space - which is substantial. Also it will be problematic with the exposed oak purlins etc. I need to use the loft for storage, but could never be used for living accommodation. What are your views on this? So is it better to:

    1. Insulate between the joists and board over (to use the loft space for storage).
    2. Insulate with kinsgpan (or equivilant) under the tiles
    3. Insulate both (say 50% in each area - or more)- allowing more space to expose some of the attractive wooden roof features?

    Any hints on materials?

    Thanks RR
    • CommentAuthortony
    • CommentTimeAug 24th 2010
     
    how rich are you?
    • CommentAuthorCWatters
    • CommentTimeAug 25th 2010
     
    RR - Not sure I follow your description but you obviously can't insulate at joist level in the areas where you want a vaulted ceiling - so options 1 and don't make any sense. You can only insulate between the rafters. You don't have to do the "loft" areas the same way. You can have a mix if you insulate the wall between the two correctly and pay attention to the vapour barrier.

    100-120mm is only just current building regs standard for a new house and is inadequate in my view.

    Have you considered removing the tiles and putting the insulation above the rafters? It would probably need planning permission but would allow more insulation and retain the exposed rafters.
  4.  
    Sorry,

    For clarification I will be lifting the ceiling height above the purlins level. Thus there will still be joists which will form a loft area / ceiling. The builder / architect have recommended kingspan 100 / 125mm between rafters. My question is can we reduce the depth of the insulation between the rafters and add additional insulation above the ceiling between the joists. Which is most cost effective? Obviuosly there will be a short run of roof between the purlin level and the main wall that will be be 'vaulted'. Apologies for poor terminology.

    Tony in answer to your question - not really, but want to insulate as cost effectively as possible.

    Cheers RR
    • CommentAuthortony
    • CommentTimeAug 25th 2010
     
    cost effective insulation = quilt or possibly recycled newspaper at the right price, thin insulation is expensive.

    Sheet insulation is tricky to retrofit and poorly done is virtually a waste of time (5% missing = 50% of heat loss still there)

    The loft void will likely be very draughty so keep all insulation at ceiling level for most efficient heat savings.
    •  
      CommentAuthorbetterroof
    • CommentTimeAug 27th 2010
     
    You need to do one or the other, between the rafters or over the joists, if you do both you are effectively making a nice warm sealed box of your loft space. You need to think of the insulation as the outer layer of your thermal envelope; below it is 'inside', above it is 'outside'. The cheapest and easiest way to do it will be to put about 300mm+ of quilt or loosefill over your ceiling joists. This will make it more difficult to utilise for storage but will give you most benefit at cost.

    As you are raising your ceiling height you must be insulating between the rafters in your new sceiling. You don't mention what your roof build up is (slate/tile/breathable membrane etc) but it is very important that you have at least 50mm airgap between your roof covering and any insulation, which obvioulsy could limit how much you can get between the rafters. As Tony says, it is very important to fit the insulation properly or you may as well not bother - if using pur board it needs sealing between the rafters with pur foam or equivalent.

    I would reccomend the following build up for your sceilings, from outside in;

    slate/tile
    batten
    breather membrane
    rafters
    75mm pur board sealed between rafters
    100mm pur board carried under rafters with fully taped joints/or with a vcl
    counter batten
    plasterboard

    If you need your loft space for storage then continue this build up through to the ridge. Pay attention to detailing and sealing/taping all edges. Try and join the roof insulation layer up with your wall insulation so it is seamless.

    If you have a bit of cash available, take the roof off, check planning, and raise your roof height a little by taking it all externally, with a build up as follows, again outside in;

    Slate
    batten
    counterbatten
    breather membrane
    100mm+ pur/woodfibre insulation (like pavadentro or similar)
    rafters fully filled with pur sealed to rafters
    vcl
    plasterboard


    Any comments?


    :bigsmile:
    • CommentAuthortony
    • CommentTimeAug 27th 2010
     
    If you need the loft for storage there is nothing wrong with building a deck in it 50mm above the ceiling insulation and putting stuff on that

    To try to create a warm loft space is fighting air infiltration and will likely loose a lot of heat, the house could even get cold on windy days.

    the best plan is not to store stuff in the loft -- recycle it or ditch it or sell it.
  8.  
    Tony / Betterroof,

    Many thanks for the information. It is very helpful. Sorry for late response, been away. The roof is an old pan tiled one with lath and plaster under. Its in a conservation area so raising the roof is not an option. The idea to retain as many orginal timbers and expose the oak pulins will not work - if I am to get more than 100mm insulation between rafters.

    The tiles have to come off anyway and ceiling come down, so I am in effect starting from stratch. This will cost c. £4-5K more but is probably better in long run. Seems my best option (if I want best insulation possible) is to replace the timbers and go for new roof, with insulation between rafters (as set out above). Loose some loft space (tony agree re storgae, but need somewhere to store somethings) and retrofit the purlins as asthetic features not structural ones.

    When talking about PUR boards etc is that what Kingspan is?

    any views? sensible approach?
    • CommentAuthorCWatters
    • CommentTimeSep 3rd 2010
     
    If the tiles have to come off I would still have a go at getting permission to raise the roof.
    • CommentAuthortony
    • CommentTimeSep 3rd 2010
     
    No I think that it way too expensive! reserved for very rare special cases where depth is a problem like window reveals.

    100 between then say 30mm PUR under or over and whatever lining material should be OK. good idea to set a target U value

    feel free to publish this if you like

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