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Housing - Renovation: Insulating wall plates

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1 to 19 of 19

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    • CommentAuthorOsprey
    • CommentTimeJun 21st 2023
     
    I have seen this discussed before, but can't find the solution.

    I am planning to have the cavities filled (eps beads) of my detached house. This will leave a cold bridge at the wall plate (see attached) and possibly mould at the tom of the bedroom ceilings (I assume). I am also planning to replace the roof.

    What is the best way to remove the cold bridge at the wall plate? Ideally, something that the roofers could install.

    Thanks for any help!
      wall plate - Cold Bridge.jpg
    • CommentAuthorphiledge
    • CommentTimeJun 21st 2023
     
    Rockwood laid on top of the cavity finishing flush with the top of the wall plate then PIR over the top of the wall plate foamed in position. Alternatively PIR glued to the outer face of the inner leaf so it sits on top of the cavity fill and finishes flush with top of the wall plate, then PIR over the top of the wall plate. We fixed a length of 32mm waste pipe to the side of each rafter as a ventilation duct so we didn't have to worry about blocking up most of the gap over the edge of the wall plate.

    Work with the roofer to start with so they know the exact detail of what you want to get the right thickness of insulation and all gaps closed up
    • CommentAuthorOsprey
    • CommentTimeJun 21st 2023
     
    Thanks Philedge. I will have to check how comfortable the roofers are with cutting PIR.

    Where there any problems in keeping the rockwool in contact with the wall leaf? There is nothing supporting it in place (from the side). I assume rockwool batts can be 'jammed' under the joist overhang.
    • CommentAuthortychwarel
    • CommentTimeJun 21st 2023
     
    To support the vertical PIR / rockwool bats etc against the inside leaf fix chicken wire or similar from the top of the outer leaf to the underside of the rafters. alternatively just lay a row of blocks on the outer leaf to bring it level with the inner.
    • CommentAuthortony
    • CommentTimeJun 21st 2023
     
    Unbelievable but there are big problems still to solve

    This is what I did 14 years ago

    http://tonyshouse.readinguk.org/mitigation-of-thermal-bridging/
    • CommentAuthorphiledge
    • CommentTimeJun 21st 2023 edited
     
    Posted By: OspreyWhere there any problems in keeping the rockwool in contact with the wall leaf? There is nothing supporting it in place (from the side). I assume rockwool batts can be 'jammed' under the joist overhang.


    We just sat the Rockwood on top of the cavity and outer leaf and the underside of the rafters held it in place. Your drawing looks to show around 200mm between top of outer leaf and top of wall plate so use 200 Rockwood cut into 200 wide strips. Once you feed it under the rafters, they'll hold it in place against the inner leaf
    • CommentAuthortony
    • CommentTimeJun 21st 2023
     
    Difficult or impossible to do unless done before sarking/sarking felt

    http://tonyshouse.readinguk.org/wp-content/uploads/2017/08/P1040088.jpg
    • CommentAuthorphiledge
    • CommentTimeJun 21st 2023
     
    Posted By: tonyDifficult or impossible to do unless done before sarking/sarking felt


    OP says roof is coming off so easy access to eaves
    • CommentAuthorOsprey
    • CommentTimeJun 21st 2023
     
    Posted By: philedge
    Posted By: OspreyWhere there any problems in keeping the rockwool in contact with the wall leaf? There is nothing supporting it in place (from the side). I assume rockwool batts can be 'jammed' under the joist overhang.


    We just sat the Rockwood on top of the cavity and outer leaf and the underside of the rafters held it in place. Your drawing looks to show around 200mm between top of outer leaf and top of wall plate so use 200 Rockwood cut into 200 wide strips. Once you feed it under the rafters, they'll hold it in place against the inner leaf


    I think the diagram overstated the gap, so maybe a bit less. I will do some experiments with rockwool.
    • CommentAuthorOsprey
    • CommentTimeJun 21st 2023
     
    Posted By: philedge
    Posted By: tonyDifficult or impossible to do unless done before sarking/sarking felt


    OP says roof is coming off so easy access to eaves


    That's the plan.
    • CommentAuthortony
    • CommentTimeJun 22nd 2023
     
    👍
    • CommentAuthorOsprey
    • CommentTimeJun 22nd 2023
     
    Posted By: philedge
    Posted By: OspreyWhere there any problems in keeping the rockwool in contact with the wall leaf? There is nothing supporting it in place (from the side). I assume rockwool batts can be 'jammed' under the joist overhang.


    We just sat the Rockwood on top of the cavity and outer leaf and the underside of the rafters held it in place. Your drawing looks to show around 200mm between top of outer leaf and top of wall plate so use 200 Rockwood cut into 200 wide strips. Once you feed it under the rafters, they'll hold it in place against the inner leaf


    Ah, I thought you meant joistsnr ther than rafters. I can see how that might work for you, but my rafters are too far away to help. So insulation would only be held by joists compressing it.
    • CommentAuthorphiledge
    • CommentTimeJun 22nd 2023
     
    The underside of your rafters look like they would cut across the edge of the insulation but probably worth doing a test. If the rafters dont hold it atall or tightly enough you could fit a batten or length of galv fencing wire between end of rafter and joist to cut across the top outer most edge of the insulation and hold it against the inner leaf??
    • CommentAuthorOsprey
    • CommentTimeJun 22nd 2023 edited
     
    Thanks for reply.

    The diagram is one I re-purposed to clarify where the problem is, rather than being drawn to scale. The actual construction is somewhat more complex (flared roof edge, very wide soffits) and I don't believe the rafters can realistically be used to hold the insulation (other tha something like the wire idea, and even then the wire would be at a low angle of incidence to the insulation, due to wide soffits).

    The best I can come up with is some sort of wire 'hook' screwed to the wood at the top of the wall plate, going across the top of the insulation and down the back. Spaced at intervals between the joists. Rather fiddly and time consuming for the roofer, I suspect. Also, rockwool easily fragments, so that may not be enough support anyway.
    •  
      CommentAuthordjh
    • CommentTimeJun 22nd 2023
     
    Chicken wire fastened to the outer leaf at the base and fastened somewhere appropriate on the rafters or joists or a batten attached to said should hold rockwool in place?
    • CommentAuthortony
    • CommentTimeJun 22nd 2023
     
    Interesting to know how much insulation you can get in over the corner of the wall plate, generally there is a 100mm gap,25mm of which is needed for ventilation

    In my book 75mm is insufficient as I now look for 400mm of loft insulation if it is quilt.
    • CommentAuthorOsprey
    • CommentTimeJun 22nd 2023
     
    Posted By: djhChicken wire fastened to the outer leaf at the base and fastened somewhere appropriate on the rafters or joists or a batten attached to said should hold rockwool in place?


    Attaching the chicken wire to the outer leaf is easier said than done, I think.
    • CommentAuthorOsprey
    • CommentTimeJun 22nd 2023 edited
     
    Posted By: tonyInteresting to know how much insulation you can get in over the corner of the wall plate, generally there is a 100mm gap,25mm of which is needed for ventilation

    In my book 75mm is insufficient as I now look for 400mm of loft insulation if it is quilt.


    I will have to do some measures, but it is more than 100mm.
    That would be nice, but perfect is the enemy of good. I would be happier with a 'lukewarm' bridge than a cold bridge.
    •  
      CommentAuthordjh
    • CommentTimeJun 22nd 2023
     
    Posted By: OspreyAttaching the chicken wire to the outer leaf is easier said than done, I think.
    Well you could glue it directly. Or attach a batten and fasten the chicken wire to that. The batten could be glued, or fastened using a few screws with plugs into drilled holes in the usual way.

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