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Roof insulation recco

Discussion in 'off topic' started by DarrenW, Aug 13, 2019.

  1. DarrenW

    DarrenW Oxygen User

    anyone have any recommendations on what to insulate between the rafters with

    It’s a 1892 Victorian semi and we have agreed to have the roof stripped, fixed and retired with the original tiles plus replacement for any dodgy ones.

    The roofer suggested if I buy some kingspan and he will fit it between the rafters whilst they have access

    Sounds sensible but I worry about condensation

    So what depth and where to get it cheaply in bulk (it’s a big roof)

    Thanks in advance
  2. zippy

    zippy pfm Member

    The thicker the better I think - 25cm if you can for fibre insulation, not sure recommended depth for Kingspan.
  3. cooky1257

    cooky1257 pfm Member

    Check your loft/house wiring isn't liable to overheating if you go nuts with the insulation.
  4. DarrenW

    DarrenW Oxygen User

    I need to leave 50mm apparently to leave a gap to avoid condensation so this should sort the overheating too

    I guess I need to know the rafter depth then put in a baton at 50mm and top the rest up with insulation, thinking 50mm should do but happy to be advised by anyone who knows rather than my google wisdom

  5. sq225917

    sq225917 situation engineer

    Kingspan, double faced.
  6. DarrenW

    DarrenW Oxygen User

    Ok interesting, why double faced?
  7. mikemusic

    mikemusic pfm Member

    Kingspan, Cellotex or other would be my choice
    On the floor of the loft is fine, nice tight fit, use foam filler in any cracks

    You need airspace if fitted under the tiles of course
  8. DarrenW

    DarrenW Oxygen User

    Sorry should have been clearer, we don’t have a floor of the loft option for 90% of the loft, it’s vaulted ceiling in the loft rooms old Victorian style
  9. sq225917

    sq225917 situation engineer

    Double faced, lower U value.
  10. DarrenW

    DarrenW Oxygen User

    Ah, no brainier then, thanks
  11. martin clark

    martin clark pinko bodger

    As SQ notes, the foil face works both ways - essentially deisgned for vapour control on the inside, lower-emissivity on the outer, but works equally both ways. Also comes for free with modern extruded insulants.

    There are many competing in this market - Kingspan, Celotex, Xtratherm, others; give,say, SIG (Sheffield Insulation group) or their competitors a call and see what they can suggest or offer. Do discuss what will fit readily /preferences with your roof contractor before ordering.
  12. steve watkins

    steve watkins pfm Member

    With regard to condensation do you not also require a breathable vapour barrier over the rafters and under the tile battens. The material being left slightly slack to allow any water to run away without running over or into any timber? Roof ridge vents?
    I would have thought that anything like this is subject to Building Regs and as such the roofer should be advising exactly what the requirements are. If you are in any doubt have a word with your local council building department and they will advise and ultimately sign any work off if necessary. All at a cost!
    A builder friend has just completed a new roof ( Victorian property) and insulation appeared to be the hottest topic as far as the council were concerned. Even to the point of not being able to patch old plaster. Needing to completely remove and insulate behind to current regs. Something to do with Thermal Elements if I remember correctly.
  13. Mongeddavid

    Mongeddavid pfm Member

    Any form of insulation to the roof requires ventilation to be provided if it is considered a cold roof construction. In the case described this can be done in two main ways. The provision of a breathable felt with a drape in the felt to allow any potential water passing the tiles to escape or by traditional felt with an air gap provided top and bottom (eaves and ridge ) . There are issues with insulation in line with the rafters if there is no triangular area at the top of the roof ( the insulation going to the apex or ridge ) then the means of ventilation at high level would need to be done via continuous ridge vents or tile vents between each rafter front and rear. Ventilation at low level dependant on what eaves detail there is could be done via soffit vents or fascia vents or indeed with tile vents but again technically it would need to be between each and every rafter. This is the only practical way if no triangle is formed at the top of the roof and is technically not ideal as there is no pressure being formed to force the arir through. If you added some collars at high level and had a small flat ceiling area the void above can be vented via one or two ridge or tile vents and the eaves as described before. In an ideal world there should be the equivalent of 10mm continuous area of vents at low level and 5mm at high level.

    This is probably confusing so feel free to PM me i can give you my number for a chat.
    martin clark likes this.
  14. gintonic

    gintonic 50 shades of grey pussy cats

    we removed some of ours as we were too hot in the upper storey, even with the loft hatch open, and windows.

    oh and no.heating on
  15. hp1

    hp1 pfm Member

    I have just done a loft conversion under a tiled and felted roof with 75mm deep rafters. I used pu foam and foiled boards on the underside of the rafters so as to leave the full depth of the rafter as an airway from ones side of the roof to the other , I also used vented soffet boards .

    I believe 75 mm is the minimum recommended air passage depth for this applicaton.
  16. DarrenW

    DarrenW Oxygen User

    seems I have 4 inch rafters so 50mm max

    my roof overhangs the property by a couple of foot and you can see the battens and back of tiles so presume this means I will need to stop the insulating at the wall and leave the breathable white membrane showing between rafters which should look better than the current but I could always board it and venilate the boards at a later date if it doesnt look ok

    thanks for the advice - seems everyone is selling 50mm double skinned celotex at the same price £19 plus vat for 8x4 give or take so will use a local merchant
  17. steve watkins

    steve watkins pfm Member

    4 inch should give you up to 100mm. I think you need to work to the regs because the work is possibly notifiable and will need to be signed off.
  18. martin clark

    martin clark pinko bodger

    50mm vent clearance is the normal applicable recommendation for the ventilation gap; If you are using a breathable sarking membrane, that's even more robust.

    Do carry the insulation through to overhang the cavity/cavity closer in the wall, if present(!) so there's no unintentional cold area here.

    If the underside of the tile is exposed in the overhang you have choices, as you mention. One would be to use a conventional sarking-felt strip as an underlay for this area, that the new membrane tail rests -on, just to mask it; much easier/cheaper than boarding-in the eaves.
  19. DarrenW

    DarrenW Oxygen User

    That’s a good idea re the conventional sarking

    My roofer tells me the membrane will look fine and I quite like the open look so prefer not to board over, will have a word with him

    One guy suggested dpc for the exposed area but that didn’t feel right

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