Insulation on solid walls

Discussion in 'Builders' Talk' started by DIY_Has123, Feb 13, 2021.

  1. DIY_Has123

    DIY_Has123 Member

    Initially I just wanted the upstairs bedroom exterior (non cavity) solid wall levelled as it's bowed and unlevelled but most people have recommended just insulating.

    So after giving this a lot of thought and considering options for fitting insulated plasterboard I have decided the best way forward is to use 2x1 treated battens fixed at 60cm centres across the wall (with dpc behind) because this wall is all over the place and out of level top to bottom and across.

    With the battens I can easily shim pack out and get them level whereas any adhesive (dot and dab or foam) won't be suitable as too many hollow voids along the wall and harder to level the boards.

    I will then fill with 25mm PIR Celotex (or other brand) between the battens and foil tape any joins or gaps. Then screw on foil backed vapour plasterboard to provide that extra vapour control layer (I heard celotex foil already provides vapour barrier). Essential the stud wall approach here.

    Will seal any plasterboard joins between boards, sockets and along perimeter with Everbuild AC50 sealant and adhesive.
    Other option was to fix on 38mm insulated plasterboard directly on top the battens but then I'd lose that inch floor space because of the batten depth.

    Does anyone see any potential problems with this approach?
  2. Severntrent

    Severntrent Screwfix Select

    No problem as such but just by adding the extra 25mm of PIR doubles the The effective U value of the wall
  3. DIY_Has123

    DIY_Has123 Member

    Hi. You mean using 38mm insulated plasterboard (which effectively has 25mm PIR) as opposed to standard 12.5mm foil backed plasterboard?
  4. Severntrent

    Severntrent Screwfix Select

    Yes, also since you have a grid of battens it gives you potential for cold spots on your wall
  5. DIY_Has123

    DIY_Has123 Member

    And so I take it putting the 38mm insulated board prevents the cold spots on the battens?

    From my research I thought cold spots was only a problem with dot and dab on solid walls.
  6. koolpc

    koolpc Screwfix Select

    I was just going to start a thread about insulating an external, solid wall.

    I have, in the past, insulated an external wall but that had a cavity. I battened the wall and put insulation inbetween the battens, vapour barrier over it all and plasterboard on top.

    Now, i want to insulate 2 solid internal walls in a different house. I wasnt sure what the best method would be?
  7. Severntrent

    Severntrent Screwfix Select

    Wood is a better insulater than plaster/dots but that does not mean you may not have problems with cold spots on wood hence the words potentially. Potential for cold spots reduced if you have a PIR interface
  8. Severntrent

    Severntrent Screwfix Select

    Why do you want to insulate internal walls?
  9. DIY_Has123

    DIY_Has123 Member

    Can these cold spots show up on the final board finished paint decoration?

    I'm not so much concerned about coldness in the room as its starting to already feel cosy with all the Rockwool I put into the ceiling before boarding up plus 100mm celotex and thinner rockwool in between the joists in floor.
  10. koolpc

    koolpc Screwfix Select

    My bad. External i
  11. Severntrent

    Severntrent Screwfix Select

    Not likely unless you have issues with condensation
  12. DIY_Has123

    DIY_Has123 Member

    Well it has been a problem wall in the past with mould and condensation. That's due to being very cold. But wouldn't the 25mm celotex keep most of this internal side of wall at least somewhat warmer than before?

    And a warmer surface means warm moist air is less likely to condense on it right.

    Last thing I want is a grid pattern of cold spot lines on the painted wall.

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