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Best way to internally insulate a solid wall

Discussion in 'Building' started by phatboy, 22 Sep 2016.

  1. phatboy

    phatboy

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    We had our house externally insulated earlier this year, with the exception of part of 1 wall as the lean-to garage is on the other side.

    I was advised at the time to internally insulate this wall.

    The wall is 9" thick solid block, and does suffer from minor penetrating damp in high winds and rain. The finish of the wall is solid, with no loose or blown plaster.

    In this case, should I be building a stud wall inside and using Celotex (or equivilent boards) between, and then plasterboard over the front?

    If this is the correct approach I have a few queries:-

    - Do I remove the floor in the 50mm gap I leave behind the new wall
    - Do I remove the ceiling in this gap?
    - If I do both of the above what should I do to prevent 'things' from getting from the under-floor space to the loft and the reverse?
    - Using Celotex foiled boards, do I need to add any other damp proof sheeting behind?

    Or is attaching foil-backed insulated plasterboard OK?

    I know the answers to some of these are listed online, but a lot is contradictory and not specific to my situation.

    Thanks!
     
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  3. motorbiking

    motorbiking

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    I think I'd either strip back to brick and then fix insulated plaster boards (e.g PL4000 range)- either on dabs or with frame fixings and then tape the joints and patch sand and paint. The thickness is up to you but even the 4025 will save a lot of heat loss, though personally I'd go something similar to the external improvement.

    There isn't any real need to create an additional internal wall
     
  4. endecotp

    endecotp

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  5. phatboy

    phatboy

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    Thanks for the suggestions.

    I may have been looking at worst case scenerio with the penetrating damp - I have never seen it in this room but have in the bathroom next to it where there has been patches of damp in hard wind driven rain below the window and behind the external soil pipe screw fixings (These have all been resolved now with the EWI hopefully).

    Outside is 90mm insulation boards, but Celotex seem to be able to meet the U value in 50mm, so I will probably play it save and go for the 60mm PL4000 range.

    I have seen a few methods, but the best looks to me to be the 'warm batten' option. So I would board the wall with the Celotex, tape all joins and batten at 600 centres vertically with 50x25mm battens, and fit some cross battens too for extra fixings. Then fill the gap around all edges with expanding foam and board it over and skim. I can avoid having an electrics or plumbing inside this wall.

    Does this seem like a reasonable way to go about it?

    Thanks again!
     
  6. John D v2.0

    John D v2.0

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    Watch the prices though, I found I could get 100mm much cheaper per m³ than 50mm. Although it's hard to cut slices if you don't want to lose room space, best to choose the thickness after you check the prices
     
  7. phatboy

    phatboy

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    Thanks John,

    In Jersey I actually think I may only have the choice of 50mm or 100mm, lack of demand for others possibly!
     
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  8. wau5

    wau5

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    the cheapest way to do it. fix some 100mm timber battens straight to the wall (no need to remove floor/ceiling) , go get some 150-170mm loft roll insulation (preferably from someone who has some left over for dirt cheap) , stick it between the studs,stick the dpm over the rockwoll/battens,screw on plasterboard, do up the plasterboard in your prefered way and you are done.


    that warm batten ''method'' sounds just wrong on so many levels...
     
  9. motorbiking

    motorbiking

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    I'd go with direct bonding method
     
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  11. phatboy

    phatboy

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    I think I'm dodging that method as I've never done it before! Maybe it's time to experiment....

    Although I'm not sure how much of a premium you pay for having the insulation boards pre bonded to the plasterboard?
     
  12. motorbiking

    motorbiking

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    I don't think you do to be honest.. 50mm celotex is about £30 a board, 50mm +12 pre-bonded pl4050 is about 36, a sheet of 12mm plaster board is about 5-6 quid. The premium is pence. The advantage is there are no battens to bridge heat and substantially better U value acheived.

    Is it the dabbing that is beyond you? there is nothing saying you can't do a bit of mechanical fixing as well.
     
  13. phatboy

    phatboy

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    Well I suppose I better request pricing for both options next week then!

    The dabbing is new to me. Could give it a go I suppose instead of avoiding. If I did it, I think I would want to put mechanical fixings through the dabs too, to be on the safe side!
     
  14. motorbiking

    motorbiking

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    yep good idea.. the advantage of dabbing is that you can get your wall perfectly level - its just like tiling, but with f** big tiles. :D
     
  15. phatboy

    phatboy

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    And I hate tiling!! As it happens, I have some 110mm plasterboard screws that I never needed, so they might get put to use then...
     
  16. motorbiking

    motorbiking

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    You need frame/hammer fixers if you are putting in to brick.
     
  17. phatboy

    phatboy

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    Good job I mentioned it then! It's blockwork behind. So if I use 50mm + PB, then I guess 100mm fixings would be OK?
     
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