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Housing - New Build: Dry lining

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  1.  
    • CommentAuthortony
    • CommentTimeSep 19th 2026 edited
     
    I looked at a new house yesterday that had been dry lined and where we measured the U-value of the walls as built, it was about half of the intentions of the design. On investigation it hadn’t been Dot and Dabbed or battened in a sense of either wood or metal battens, but rather they had used strips of plasterboard effectively as battens presumably dubbed out to plumb and flat using a laser and then applied the plasterboard onto those. They must have use either drywall adhesive or foam to stick it all together. There is no evidence of metal fixings on the thermal images. The house is brick cavity block construction with aerated concrete blocks on the inner skin and the cavity has been nicely filled with platinum expanded polystyrene beads.

    I can’t see why the U-value is so bad, but I think that outdoor air must be getting in between the blockwork and the plasterboard.

    Any ideas or help, please?
  2.  
    Perhaps wait until the weather is a bit colder, put the heating on for a bit then have a look with a thermal camera to try to determine where the problems are.

    BTW out of interest you say new build, is it a self build or done by one of the big boys and how new is new.
  3.  
    Where is the airtight layer supposed to be, is it the plasterboard? That will pass a blower test from the inside but cold air can circulate just behind the p/b, (as you showed on your excellent website!)

    The void behind the plasterboard is probably open to the loft or subfloor and there are 1001 micro gaps in the block work mortar so outdoors air is seeping behind the p/b. If you take a socket off on a windy day, does cold blow out?

    Can you remove a sheet of the plasterboard and thermal image the blocks behind it? In theory they should be warm because of the cavity fill, but in practice there may be cold air leaks

    Was working on a cavity wall like that last January, with my eyes closed I could find the mortar lines in the blocks by feeling the cold seeping through!

    The plasterboard 'battens' are bit different from normal but don't affect the airtightness (or lack of) compared to using normal studs or dabs.

    Ideally take all the plasterboard off and replace with wet plaster or insulated plasterboard, but that's easier to say than to do.
    •  
      CommentAuthordjh
    • CommentTimeSep 19th 2026
     
    Posted By: WillInAberdeenIdeally take all the plasterboard off and replace with wet plaster or insulated plasterboard
    Agree about wet plaster but I doubt insulated plasterboard has sufficient insulation to deal with cold air on its outside?
  5.  
    Tony coined the phrase 'plasterboard tent'! I'm sure that if it's him replacing the plasterboard, then it will have a combed adhesive bed with no air movement behind it, while taking the opportunity to add insulation and improve U value.

    Insulated plasterboard comes in different thicknesses, you can use it thick enough that no other insulation is required if that's the scenario, but obvs that extra thickness has knockons. In this case if air movement is proven to be the problem and some credit is given for the cavity fill, then a lower thickness would be optimum.

    https://insulationgo.co.uk/122mm-123mm-110mm-unilin-xt-tl-pir-insulated-plasterboard-drylining-walls-laminate/



    Whenever we discuss people putting EWI on cavity walls, filled or not, this is the scenario that comes to mind. If the outside air is circulating behind the plasterboard then pretty likely it is also circulating through the cavity fill as well, EPS beads are not airtight. If there is insulation bonded in firm contact with the back of the plaster/board then there is no question of air movement being a problem.
    • CommentAuthorowlman
    • CommentTimeSep 20th 2026
     
    "Dot and Dab, Blob and Dob " Mmm, terms for incorrectly applied drywall adhesive and followed literally by many, too many. It should be continuous thick trowelled beads especially round all 4 sides and electrical cut-outs and on lumpy walls.
    It uses a lot of adhesive if done correctly.
    • CommentAuthortony
    • CommentTimeSep 21st 2026
     
    Peter, big house builder , one of the better ones supposedly
    • CommentAuthortony
    • CommentTimeSep 21st 2026
     
    The plasterboard ‘battens, can be from the loft down the gap between the plasterboard ceiling 15 to 18mm. It is continuous and we can’t get a liege of paper between it and the blockwork.

    Can’t see how it is fixed or how the plasterboard is fixed to it, I suspect foam.

    I agree that EPS beads are not airtight but they significantly resist air movement.

    We are planning monitoring on a windy day and a calm day.
    • CommentAuthorArtiglio
    • CommentTimeSep 22nd 2026
     
    Real world building control and quality control are very distant from what’s written in the regs. Most of the trades work on tight prices and bish bash bosh is the order of the day ( i’ve seen door linings fixed in with 3” wire nail, hammered flush, decorator just painted over them after a cursory wipe of filler. Local new build estates have had seemingly endless amounts of work redone. And that’s just the obvious visible exterior works).

    It’s not without reason that Assent ( the building control provider) shut down, leaving many people in the lurch. Me included, the inspectors i’d had had filed no post inspection reports. I’ve had to revert to council building control at not insignificant cost. Fortunately they were satisfied with the pictures i’d taken during the build and the emails i’d had with Assent regarding various aspects of the works.
  10.  
    Declaring an interest: we're Build4less, a building materials supplier, but this is a diagnosis question rather than a product one.

    Tony, your comment that the plasterboard battens run up into the loft past the ceiling board is probably the key. If the void behind the linings is open at the wall head, cold loft air can drop straight down behind the boards, and once there is a gap at both top and bottom you get a convective loop running behind the plasterboard, even on a calm day. That alone can wipe out a large share of what the cavity fill is doing, because the inner leaf ends up sitting in air at close to loft temperature.

    The other usual routes on dry lined block houses are the intermediate floor zone, where the void behind the linings often runs straight past the joists and into the floor void, and the skirting line at ground floor, where it links into the gap under the screed or the suspended floor.

    A cheap test before taking anything off: go into the loft and seal the top of the void along one wall with foam or airtight tape for a few metres, then compare heat flux readings on that wall against an untreated one in the same conditions. If the sealed section improves noticeably, you have your answer, and the fix may be sealing the head, the floor zone and the skirtings rather than stripping out. A smoke pencil at sockets and skirtings with the house depressurised by a blower door will also show where air is coming out of the void.

    Your windy versus calm day comparison should separate the two effects nicely. Wind washing through the blockwork mortar and the EPS beads will track wind speed, while a stack driven loop from the loft will be there regardless of wind and will get worse as the outside temperature drops.

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