Cellotex to underside of rafters

Discussion in 'Builders' Talk' started by web, Oct 5, 2013.

  1. web

    web New Member

    What is the best way to fix 65mm cellotex to the underside of rafters ? I cant fit it in between the rafters as underfelt has already been fitted in between the rafters.....screws, nails ?

    Thanks
  2. Sean_ork

    Sean_ork Screwfix Select

    have you considered the fact that most loft spaces need to have a good flow through of air to keep them vented, and vapour free - by insulating, and blocking the ventilation paths you could be creating a big problem for the future
  3. web

    web New Member

    Hi Sean

    yes I realise that - i would leave an air gap between the insulation and the felt/tiles, and most of the soffits are ventilated, so there should still be a reasonable air flow. The loft is boarded out with some rockwool below, insulated loft boarding is very expensive, and the loft leg means you have to get the legs in exactly the right positions to support the boards - tricky ! this is why I am looking at this option. comments welcome.........
  4. Sean_ork

    Sean_ork Screwfix Select

    standard 19x38 roofing battens across the joists, 400mm to 600mm centres to space the boarding off the joist faces - screws and washers to pin boarding to the battens, if you want a proper finish then sink fixing below flush and use long plasterboard screws through PB and PU into batten, foil tape the joins

    have you consider a multifoil such as ........... some detailing images should illustrate the fixing

    http://www.ybsinsulation.com/products_roof_superquilt_under.htm
  5. web

    web New Member

    Hi Sean, re multifoil just looking into that...........bit concerned about it sagging, also will fixings ruin the performance ? the advantage is it comes in rolls so might be able to get it through loft hatch 64mm x 58mm, as boards will have to be cut to get them up there - appreciate your comments.......
  6. web

    web New Member

    Hi Sean, Brilliant, thanks, this web link is just what I need !
  7. Sean_ork

    Sean_ork Screwfix Select

    it won't sag unless you allow it to when you fix it, by not pulling it taut - there's a few videos showing the installation methods on the YBS site, you'll see how few fixings are needed, especially if it's battened below - so performance loss isn't an issue

    over sailing entire sheets of rigid 2400x1200 rigid sheets is a great way to insulate, but, as you have mentioned - the average loft hatch is somewhat smaller

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