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    • CommentAuthorskyewright
    • CommentTimeApr 6th 2015 edited
     
    I'm thinking about adding insulation to the wall between the house and an unheated conservatory. The existing wall is 1970 cavity block, with a thick rough-cast cement render and with retro-fit blown in glass fibre insulation

    Additional insulation could be 25-50mm internal, &/or 50-100mm external.

    If we used PIR, 50mm would give something like U=0,16 & 100mm U=0.11.

    I think the (semi-)external option would be better? It would certainly be easier!

    However, being original 1970 construction (aside from the CWI, & the conservatory, come to that) there's no vapour barrier inside, just plaster board, then a gap, then the first layer of block. I've never seen any sign of interstitial condensation (I cored a hole through the wall last Christmas). If we were to add vapour barrier to the inside it would probably be little additional effort to add a bit of insulation at the same time.

    Any thoughts?
    • CommentAuthorowlman
    • CommentTimeApr 6th 2015
     
    I'm unsure that adding additional insulation either in or outside, on just the section of wall where the conservatory abutts would make a real significant difference.
    I suppose you could argue that extra insulation hinders the passage of solar gain heat into the house from the conservatory.
    Is there a lot of wall area involved?
    • CommentAuthortony
    • CommentTimeApr 6th 2015
     
    EPS EWI 100mm
  1.  
    I would certainly go with the external option, but have you considered spending the money on:

    a) an upgraded conservatory/garden room, which would do the same job and add value?
    b) removing the conservatory and doing proper EWI over that side?

    If it's a run down conservatory, I would be inclined to use something that will work as EWI should you remove the conservatory in 10 years time, otherwise you will need to take it all off again or seal it!

    Ferdinand
  2.  
    Posted By: owlman
    Is there a lot of wall area involved?

    Yes. It's a bungalow and the conservatory covers all bar 0.5m at either end of the wall (13.6m out of 14.6m).

    Posted By: owlman
    I suppose you could argue that extra insulation hinders the passage of solar gain heat into the house from the conservatory.

    I wondered about that. We get a lot of solar gain, most obviously by ventilation (i.e. opening doors & windows), but some will be stored in the walls.
    • CommentAuthorskyewright
    • CommentTimeApr 6th 2015 edited
     
    Posted By: ferdinand2000a) an upgraded conservatory/garden room, which would do the same job and add value?
    b) removing the conservatory and doing proper EWI over that side?

    It's a newish conservatory, in good condition and to full current building regs.
    We are in a very exposed location. The conservatory provides considerable passive gain and "insulation benefit"[1] in itself (as well as providing useful growing space).

    [1] I think I made that term up? i.e. IIUC, if it's 0C "outside", 20C "inside" and 5C in the conservatory then heat loss through the covered wall is reduced by ~25% compared to through a real external wall, heat loss being approximately proportional to temperature difference (at human friendly temperatures). Maybe there's a proper name?
  3.  
    Would you perhaps get a greater benefit by applying your EWI to a different wall which does not have the protection of the conservatory?

    Judging by your comments though, you have probably considered this already.

    F
  4.  
    Posted By: ferdinand2000Judging by your comments though, you have probably considered this already.

    Yes, considered.
    There's a conservatory as described above both front & back, so that only leaves the gable ends as fully eternal. The gables may be an option some day, but not in the foreseeable future (& I'd certainly want to see an equivalently exposed example that had seen a few years worth of weather), Aside from anything else, inside the conservatories EWI would be a simple DIY job requiring no special technical finishes & so on.

    Thanks for your input, nonetheless.
  5.  
    Posted By: tonyEPS EWI 100mm

    So EPS rather than PIR.
    Cost/benefit? Or something else?
    • CommentAuthorEd Davies
    • CommentTimeApr 6th 2015
     
    Greater permeability of EPS, rather than PIR, I'd assume. If it's sufficiently permeable that it hardly adds to the vapour resistance provided by the existing cement render then it's pretty much sure to be safe from the interstitial condensation point of view.
  6.  
    Posted By: Ed DaviesGreater permeability of EPS, rather than PIR, I'd assume.

    Thanks Ed. Makes perfect sense.
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