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Any thoughts on EPDM roofing for an single storey extension

  • 22-04-2021 1:16pm
    #1
    Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    60 m2

    on 200mm kingspan
    on VCL
    on 22 mm marine ply
    on furring pieces for a 1:40 slope
    .
    Summer over heating?
    Its 31% of all roof area so is insurance an issue?

    Is the VCL not a water of money based on the XPS and the EPDM being 100% impermeable


Comments

  • Registered Users Posts: 30,321 ✭✭✭✭ Penn


    Is the VCL not a water of money based on the XPS and the EPDM being 100% impermeable

    Water and Water Vapour are two different things. The VCL prevents water vapour entering the roof construction from inside due to the different pressures between interior and exterior, and therefore help to prevent interstitial condensation.


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    Penn wrote: »
    Water and Water Vapour are two different things. The VCL prevents water vapour entering the roof construction from inside due to the different pressures between interior and exterior, and therefore help to prevent interstitial condensation.

    The joists are underneath the VCL and the xps is foiled backed both sides...


  • Registered Users Posts: 30,321 ✭✭✭✭ Penn


    The joists are underneath the VCL and the xps is foiled backed both sides...

    The foil deals with thermal movement, not moisture. Taping the joints between same also won't be comparable to a VCL.

    You could put the VCL on the inside of the timbers behind the plasterboard, but generally it should just go directly on the warm side of the insulation.


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    Penn wrote: »
    The foil deals with thermal movement, not moisture. Taping the joints between same also won't be comparable to a VCL.

    You could put the VCL on the inside of the timbers behind the plasterboard, but generally it should just go directly on the warm side of the insulation.
    So you could use 1200 gauge plastic


  • Registered Users Posts: 521 ✭✭✭ SC024


    Penn wrote: »
    The foil deals with thermal movement, not moisture. Taping the joints between same also won't be comparable to a VCL.

    You could put the VCL on the inside of the timbers behind the plasterboard, but generally it should just go directly on the warm side of the insulation.

    Is it not the same as foil on foil backed plasterboards?


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  • Registered Users Posts: 30,321 ✭✭✭✭ Penn


    SC024 wrote: »
    Is it not the same as foil on foil backed plasterboards?

    Basically, but the trouble with both is having to tape the joints. Even then though I don't think the foil is equivalent to an actual vapour control layer. Particularly with the insulation as you'd have to rely on very tight fit of the boards, and you can only tape the joints on the exterior side which could still allow water vapour between the joints in the insulation sheeting.


  • Registered Users Posts: 30,321 ✭✭✭✭ Penn


    So you could use 1200 gauge plastic

    Think so, yeah. I think as it's on the cold side of the timbers (being between the insulation and the timber sheeting/joists) it should be fine.


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    60 m2

    on 200mm kingspan
    on VCL
    on 22 mm marine ply
    on furring pieces for a 1:40 slope
    .
    Summer over heating?
    Its 31% of all roof area so is insurance an issue?

    Is the VCL not a water of money based on the XPS and the EPDM being 100% impermeable

    How is kingspan fixed to vcl/ply?
    No over heating issue.
    Ring insurers.
    The joints of the kingspan are not impermeable. Put in the vcl.


  • Subscribers Posts: 36,237 ✭✭✭✭ sydthebeat


    There's a big difference between "vapour control layers" and "vapour barriers".

    VCLs are 'intelligent' in that they close in cold winter weather and stop internal vapour entering the construction from the warm air... But in summer they open to allow vapour travelling the other direction to pass through the construction on order to exhaust internally.

    Vapour barriers, such as 1200 gauge polythene, foil backing etc don't allow this vapour permeability so their use may cause unintended issues.


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    Right so
    EDPM
    on 200mm kingspan
    on VCL
    on 22 mm marine ply

    Am assuming the ply is across the flat roof joists


    Is the EDPM breathable?
    If not then the VCL serves no purpose?


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  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    Right so
    EDPM
    on 200mm kingspan
    on VCL
    on 22 mm marine ply

    Am assuming the ply is across the flat roof joists


    Is the EDPM breathable?
    If not then the VCL serves no purpose?

    The ‘vapour control layer’ stops internal moisture getting into the roof build up. That’s the purpose.


  • Registered Users Posts: 859 ✭✭✭ homewardbound11


    60 m2

    on 200mm kingspan
    on VCL
    on 22 mm marine ply
    on furring pieces for a 1:40 slope
    .
    Summer over heating?
    Its 31% of all roof area so is insurance an issue?

    Is the VCL not a water of money based on the XPS and the EPDM being 100% impermeable


    Is this not a warm roof construction detail used slot in the UK.
    a lot of garden rooms seem to be constructed this way .
    A good question on the coil back insulation . Surely any fixing pins would penetrate the vapour control layer onto the waterproof marine ply .


  • Registered Users Posts: 1,071 ✭✭✭ PMBC


    Cross ventilation not required as this is a warm flat roof; right?


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    Just looking at this roof again from the view point of a U value, so looked on line and it seems the EDPM requires ply
    so is this makeup description wrong?

    EDPM
    on 200mm kingspan
    on VCL
    on 22 mm marine ply


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    How is the epdm adhered to the kingspan?

    Not sure you answered how the vcl and kingspan were adhered to the ply?


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    BryanF wrote: »
    How is the epdm adhered to the kingspan?

    Not sure you answered how the vcl and kingspan were adhered to the ply?

    I didn't 'cause all I have is a drawing with that sequence written on it and a client who knows zip!


  • Registered Users Posts: 25 hydrus21


    You would need to use Kingspan TR31 or similar which has 6mm ply faced on one side. The epdm is bonded to this ply.
    Epdm is a breathable membrane.


  • Registered Users Posts: 1,071 ✭✭✭ PMBC


    Im going to use
    EPDM on
    120mm single board Kingspan TR27
    on VCL
    on 18mm OSB ?Sterling Board
    on firring pieces on C20 or C24 joists
    with 12mm plasterboard under
    U value just better than 0.20
    although I may still opt for the fibreglass 650 mat


  • Subscribers Posts: 36,237 ✭✭✭✭ sydthebeat


    PMBC wrote: »
    Im going to use
    EPDM on
    120mm single board Kingspan TR27
    on VCL
    on 18mm OSB ?Sterling Board
    on firring pieces on C20 or C24 joists
    with 12mm plasterboard under
    U value just better than 0.20
    although I may still opt for the fibreglass 650 mat

    youd be mad not to install some quilt between those ceiling joists... might allow you to reduce the depth of the TR27.


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  • Registered Users Posts: 30,321 ✭✭✭✭ Penn


    sydthebeat wrote: »
    youd be mad not to install some quilt between those ceiling joists... might allow you to reduce the depth of the TR27.

    I wouldn't. Your insulation is better in one layer and 120mm rigid insulation isn't too bad. You could install 100mm quilt between the joists to reduce the rigid by about 30 or40mm, but then you've some thermal bridging through the roof timber, not to mention extra fittings required to hold the quilt against the underside of the ply/OSB.

    Easier and more effective to go with the rigid and shouldn't be that different in cost either.


  • Registered Users Posts: 252 ✭✭ Biker1


    PMBC wrote: »
    Im going to use
    EPDM on
    120mm single board Kingspan TR27
    on VCL
    on 18mm OSB ?Sterling Board
    on firring pieces on C20 or C24 joists
    with 12mm plasterboard under
    U value just better than 0.20
    although I may still opt for the fibreglass 650 mat

    You will find that that build-up will give a U-value of 0.14w/m2k.


  • Registered Users Posts: 1,071 ✭✭✭ PMBC


    Thanks last three posters.
    When I thought about it I changed to
    EPDM on
    18 mm OSB Sterling board on
    120mm Kingspan on
    VCL on
    12 mm Ply
    on softwood firring pieces across
    joists with plasterboard under.


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    It’s all about the wall junctions for vcl & insulation overlap. Also how is vcl adhered & insulation adhered to vcl.


  • Registered Users Posts: 1,071 ✭✭✭ PMBC


    Nor sure Bryan if Im picking you up correctly - vcl will be laid on top of the (sub-decking) ply or OSB. I havent thought about the eaves - yet. Also I need to figure out possible cold bridging at the eaves and side walls.


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