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General: breaking the thermal bridge of my metal sip panels at the roof and wall junction

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  1.  
    • CommentAuthorthebeacon
    • CommentTimeApr 3rd 2023 edited
     
    Hello,

    I have a question about breaking the thermal bridge of my metal sip panels at the roof and wall junction.

    I have been designing my garden room using Kingspan QuadCore Insulated Composite Roof Panels (KS1000RW) (https://www.steelroofsheets.co.uk/products/kingspan-ks1000rw-quadcore-insulated-composite-panels/) sitting onto the timber frame. The timber frame has 90mm pir insulation in it. The walls then have a 70mm Kingspan Quadcore AWP Micro-Rib Wall Panels externally cladding to reduce the thermal bridging in the walls (https://www.steelroofsheets.co.uk/products/ks1000mr-kingspan-micro-rib-composite-panels/).

    I have overlooked the junction of the roof and wall and have realised that there will be a thermal bridge between on the underside of the roof panel going from the inside of the room to the overhang of the roof on the exterior. I have thought of a few ideas to solve this, but would like to know if anyone has any thoughts or suggestions?

    The ideas I have thought of:

    1. Cut the underside of the SIP with a circular saw just deep enough so it only cuts the metal. Make this cut where the panel hits the middle of the bearing wall. The only metal skin removed is the width of the saw cut. The roof panels are attached and supported with matching metal from the SIP supplier screwed to the outside of the wall and the bottom side of the roof panel. The metal is bent to match the angle created by the intersection of the wall and roof panel. My concern with this is the structural integrity of the panels. The overhang at the front of the room is no more than 700mm and I don’t intend to stand on it.

    2. Insulate the underside of the overhang on the outside with 30mm pir. This would essentially insulate the area that would cause the thermal bridge.
      small-IMG_3611.jpg
      smallsmallScreenshot-2023-04-03-at-07.49.25.jpg
  2.  
    Option 2 for me. Add the insulation, thicken the roof visually as 90mm would "look" quite weak.

    You'll be adding a metal flashing on top of the roof edge, running over the side to give a facia, likely a 150x150 or 200x200. Run a timber perimeter under the insulation soffit, and this flashing will fix to that (in the vertical plane). Then the soffit void can be filled with insulation, butting against the wall panel. I'd prob use a wool/batt, so it hugs the profiles of the roof and wall panels.

    Have you drawn out the detail at the low end of the roof, where the gutter attaches? I think that might affect your answer to this (perhaps over concern) of cold bridging? ie. cutting back the lower steel skin and insulation to let-in the gutter.

    You may not "plan" to stand on the edges, but someone else may do so.
    • CommentAuthorthebeacon
    • CommentTimeApr 4th 2023
     
    Thanks for your reply. All valid points.

    Posted By: GreenPaddyHave you drawn out the detail at the low end of the roof, where the gutter attaches?


    The panels come with a cutback, usually 75m, but they can do custom. I think the cutback works to my advantage as I will have the space to stop the thermal bridge and fix the guttering. It will be a less than 100mm overhang at the back.

    I have drawn revised plans taking into consideration your response.
      design2-small.jpg
  4.  
    Hi, I encountered similar issued previously, these details evolved http://www.viking-house.ie/timber-frame-warm-stud.html The Canadian House Building Manual says "1cm EPS on top of a rafter reduces its condensation risk by 90%.
    •  
      CommentAuthordjh
    • CommentTimeApr 19th 2023
     
    I don't think there are any rafters with this SIP panel roof?
  6.  
    I know, they're metal stud.
    •  
      CommentAuthordjh
    • CommentTimeApr 19th 2023
     
    Posted By: Viking HouseI know, they're metal stud.
    Sorry, don't understand? The problem AIUI is that the SIP has metal surface coverings that form a thermal bridge. There are no studs or rafters AFAIK.
  8.  
    Ok I read it again, the OP's talking about cutting the underside steel, I thought he was talking about cutting the steel where the sheets join, or is there any?
    • CommentAuthorcjard
    • CommentTimeApr 24th 2023
     
    Before worrying about it too much remember that the think that thermally breaks an alu window is less than an inch of plastic :)

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