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Housing - Renovation: Insulating on top of suspended timber floor and making air tight

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    We made a decision to insulate on top of our suspended timber floors (1960s bungalow) with 100mm PIR and then float 18mm chipboard flooring panels.

    Following a little research, this is our current approach:

    - fit the celotex or similar wall-to-wall
    - Put an airtight membrane on top of the insulation - will heavy duty polythene sheet be ok, or is there a recommended better alternative
    - fold it up the old plastered wall / plaster boarded walls (we have split a large room with stud walls) then tape it before plastering over it
    - float the chipboard floor panels on top of the polythene leaving a small gap for expansion

    I see the stud work as a thermal bridge through the insulation and also compromising air tightness, should we insulate inside the bottom of the stud wall?

    We will airtight tape any electrical wire that comes up through the floor into the wall.

    Is there anything else sensible that we can do to mitigate air coming up from the floor into the stud wall between the wood frame and plasterboard? I guess we could put some kind of double sided tape on the wood frame before fixing the plasterboard.

    Anyone done something similar and have any product suggestions?

    Thanks in advance
    • CommentAuthortony
    • CommentTimeAug 21st 2023
     
    Doors will need lintels raising

    Polythene is a good choice.

    I would build stud wall on top of the floating floor! 15mm gap at edges.

    Trap poly behind skirtings
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      CommentAuthordjh
    • CommentTimeAug 21st 2023
     
    I suspect the 18 mm chipboard might be a little bouncy and would suggest using the thicker 22 mm T&G type. Fill the small gap around the edge with something compressible (cork?) to prevent the floor moving over time.
    • CommentAuthorphiledge
    • CommentTimeAug 21st 2023
     
    Half our ground floor is 18mm chipboard floating floor on either PIR or polystyrene. So long as the base is flat theres no movement in the insulation and no where for the flooring to move to. Make sure you fully glue all the chipboard joints, pull the boards together tight and dont walk on it til the glue has set unless you've laid another board(s) over the top at 90 degrees to work off while the glue is drying.
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      CommentAuthordjh
    • CommentTimeAug 21st 2023
     
    Posted By: philedgeno where for the flooring to move to
    I'm talking about side-to-side movement if there is a gap around the edge.
    • CommentAuthorJeff B
    • CommentTimeAug 21st 2023
     
    I used a special putty to seal around cables where they passed through insulation/plasterboard. Easy to work with and guaranteed to make a decent seal. Presumably safe for use with electrical cables as they are advertised to be used for that very purpose.

    https://www.superlecdirect.com/r391-electrical-weathproof-compound-2x250g/?utm_term=&utm_campaign=&utm_source=adwords&utm_medium=ppc&hsa_acc=5149061780&hsa_cam=18307518856&hsa_grp=&hsa_ad=&hsa_src=x&hsa_tgt=&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gclid=EAIaIQobChMI1ovhpN7ugAMVBIbtCh3eIAIiEAQYFSABEgLxf_D_BwE

    Other similar products are available!
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      CommentAuthordjh
    • CommentTimeAug 22nd 2023
     
    For airtightness I would tend to rely on tapes or other products designed for that express purpose.

    Posted By: GreenApprenticeIs there anything else sensible that we can do to mitigate air coming up from the floor into the stud wall between the wood frame and plasterboard? I guess we could put some kind of double sided tape on the wood frame before fixing the plasterboard.
    I'm not sure I understand the situation or the possible cure?
  8.  
    Thanks all.

    We’ve already built the walls over the floorboards and it would have been a bit chicken and egg to lay the floating floor first as we need to get electrics into the wall, plumbing for en-suite, etc.

    Posted By: djhFor airtightness I would tend to rely on tapes or other products designed for that express purpose.


    I’ve since seen double-sided expanding airtight tape that will do the job between the plasterboard and the framework

    Posted By: philedgeHalf our ground floor is 18mm chipboard floating floor on either PIR or polystyrene. So long as the base is flat theres no movement in the insulation and no where for the flooring to move to. Make sure you fully glue all the chipboard joints, pull the boards together tight and dont walk on it til the glue has set unless you've laid another board(s) over the top at 90 degrees to work off while the glue is drying.


    Will do, we saw a video of someone using expanding glue for the chipboard flooring, expanding glue, who knew!
    • CommentAuthortony
    • CommentTimeAug 23rd 2023
     
    I love expanding wood glue but am am old fashioned and tight fisted and used to use pva sparingly 300mm on 300mm off like a dotted white line in the toad. Full run on the ends, using too much glue can cause wood to swell, foam glues are great but can force joints apart
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      CommentAuthordjh
    • CommentTimeAug 23rd 2023
     
    Posted By: GreenApprenticeI’ve since seen double-sided expanding airtight tape that will do the job between the plasterboard and the framework
    I still don't understand what "the job" is?

    Will do, we saw a video of someone using expanding glue for the chipboard flooring
    Yes that's the normal D4 glue
  11.  
    Posted By: djhI still don't understand what "the job" is?


    We’ve split a large room that has a timber suspended floor into four separate spaces by building stud walls over the floorboards. We’re installing a floating insulated floor and making airtight to plasterboard on the studs. I was worried that air would come up through the old floorboards into the stud wall - between the plaster board and wood.

    Thinking about it again, we could make airtight to the stud wood before plaster boarding which will require adding some more noggins and rethinking the order of events re wiring and plumbing.
  12.  
    When I build a stud wall I start by fixing a 2x4 to the floor then a 2x4 to the ceiling then the verticals between the two with noggins as required, after this I put wool type insulation between the studs as sound deadening after which comes the plasterboard. With this build up I don't think any air flow will be coming up into the stud wall.

    Any electrics in the wall have to take note of the appropriate de-rating requirements.
    •  
      CommentAuthordjh
    • CommentTimeAug 24th 2023
     
    Posted By: Peter_in_HungaryWhen I build a stud wall I start by fixing a 2x4 to the floor then a 2x4 to the ceiling then the verticals between the two with noggins as required, after this I put wool type insulation between the studs as sound deadening after which comes the plasterboard. With this build up I don't think any air flow will be coming up into the stud wall.
    If you were concerned about the possibility then you need to put an airtight membrane/gasket on the floor under the 2x4 before you start building the stud wall, and connect that to airtightness membrane on the floor in the rooms. Or any other solution that runs connected airtightness over/under/through the whole floor surface.

    Any electrics in the wall have to take note of the appropriate de-rating requirements.
    Electrics in a stud wall are normally clipped to the studs so aren't surrounded by insulation and don't need to be derated, I believe.
    •  
      CommentAuthordjh
    • CommentTimeAug 24th 2023
     
    Posted By: GreenApprenticeThinking about it again, we could make airtight to the stud wood before plaster boarding which will require adding some more noggins and rethinking the order of events re wiring and plumbing.
    Airtightness needs thinking about at the design stage before construction. Maybe you can use airtightness paint over the whole bottom of the stud wall and neighbouring floor? Then connect that to your polythene membrane.
  15.  
    Posted By: djhElectrics in a stud wall are normally clipped to the studs so aren't surrounded by insulation and don't need to be derated, I believe.

    Electrics in a stud wall need derating depending upon where in the stud wall they are fixed

    https://www.elandcables.com/media/3hoka0mu/table-4d5.pdf
    E.g. a cable in a stud wall not touching the wall surface will need to be derated by about 50% from nominal.

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