Insulate cold solid wall

Discussion in 'Builders' Talk' started by Seabream1995, Apr 28, 2024.

  1. Seabream1995

    Seabream1995 New Member

    Hi just wanted a bit of advice ime planning on insulating a solid internal wall my method is batten the walls with 25mm batten with a strip of dpc behind them put 25mm celotex insulation in-between and tape over over joints and battens with foil tape place a vapour barrier over this and then foil backed plasterboard on top. Having looked online most are showing that the insulated plasterboard should be fixed on top of the battens which would mean there would be an air gap behind I can't understand if the air gap is kneeded or it's just because obviously that's the only way u could do it with insulated board it also shows can bond it using foam which would mean there was no air gap anyway I would of thought having no void or air gap would be better as everything is going to be air tight and it's not as if there's going to be any air flow behind there anyway if did leave a gap. My question is do I kneed that air gap there as its far cheaper to do it my method and also saves more floor space. Thanks.
     
  2. Larry_129

    Larry_129 Active Member

    What is the outer side of the wall like? Rendered, painted, and with what?
     
  3. Alan22

    Alan22 Screwfix Select

    Generally external walls have an air gap of 50mm, internal brick walls as you suggest.
     
  4. Mark DM

    Mark DM Screwfix Select

    If its an internal as you state rather than external wall that you want to insulate you won't need VB, dpc air gap or foil backed plasterboard. If external you will need air gap and foil backed board incorporated.
     
    Last edited: Apr 29, 2024
  5. Seabream1995

    Seabream1995 New Member

    Thanks all and sorry it's the internal side of an external wall if that makes sense rendered with sand and cement on the outside
     
  6. Seabream1995

    Seabream1995 New Member

    Do u think I could use foam adhesive to stick the insulated board directly to the wall and scrap the batten idea just there won't be an air gap then is whats confusing me
     
  7. Pocah

    Pocah Member

    Yes.



    Depends how "pro" you feel. Batons are more DIY because you have time to mess with them and get things right.
     
  8. Seabream1995

    Seabream1995 New Member

    Thanks
     
  9. Severntrent

    Severntrent Screwfix Select

    Depends if you are at ease with no dampness at all permeating from the outside and affecting the long term adhesive effectiveness of the foam, the video looks like the boards are being placed on double skin walls. Kingspan brochure K118 has the following caveat about dot and dabbing to solid walls -This method is not suitable for use directly on non rendered solid masonry walls where there is a risk of moisture penetration . As for air gaps or not, as you say, they are usually there because of using insulated board which in effect help with the end U value of the wall slightly (a bit like the air gap in past house construction), filling the gap with insulation improves the end U value (a bit like the air gap in current house construction is filled with insulation material) Opting for infilled batten as per your original idea gives a higher U value (which is a bad thing) than gap and insulated plasterboard (assuming same insulation thickness as used for gap filling) due to cold tracking through battens to plaster board which doesn't happen if you have insulation over the battens. The changes to U values whichever way you go will be slight so its a case of "you pays your money and you takes your choice"
     
  10. Seabream1995

    Seabream1995 New Member

    Thanks for taking the time to write back ime going to have a rethink now and read through the k118 brochure
     
  11. Alan22

    Alan22 Screwfix Select

    The reason for the air gap is to allow air to move between the wall and insulation and naturally vent and evaporate any damp, external walls can be cold and create a dew point, sticking insulation straight to the wall can give you a dew point trapped against the wall and damp.
     
  12. Seabream1995

    Seabream1995 New Member

    Thanks for the feedback having read the k118 brochure it does say one of the methods of fixing is using plasterboard pu foam adhesive which means there would be little to no gap at all it doesn't mention anywhere about kneeding an air gap so I can't see the problem with my original idea if there boards are touching the wall with no air gap then the only difference with my idea is I will have no insulation were the battens are I don't see this making alot of difference. I would have thought having the insulation directly to the wall would also warm the wall more then an air gap would
     
  13. koolpc

    koolpc Super Member

    Some good info here:

     
  14. Severntrent

    Severntrent Screwfix Select

    Except when you fix insulated plasterboard to internal faces of existing walls with floors and ceiling with battens there is no venting of the trapped air??
     
  15. koolpc

    koolpc Super Member

    I get a lot of that myself, trapped air!
     
  16. Severntrent

    Severntrent Screwfix Select

    After watching that video I'm not surprised
     
  17. Larry_129

    Larry_129 Active Member

    Have you considered wood fibre insulation?
    I have used this on a solid wall and v happy.
    Happy to share more about my experience if that's useful to you but it significantly mitigates the damp risks.
     
  18. Alan22

    Alan22 Screwfix Select

    There is no rain on the other side of internal walls, both sides are stable.
     
  19. Severntrent

    Severntrent Screwfix Select

    The horse will be happy then
     
    Alan22 likes this.
  20. glob@l

    glob@l Screwfix Select

    I would be very interested in your experience with fibre board insulation. Thank you. Perhaps a fresh thread though?
     

Share This Page