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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorGarethC
    • CommentTimeDec 21st 2017 edited
    I looked into injecting EPS beads between the studs behind my period lath and plaster wall, but, a) couldn't find anyone to do it, and b) on inspection, the cavity between the studs is really thin and uneven, so it would have been awkward and might not have performed well anyway.

    I've got period cornices and all sorts of 'stuff' on my walls, so 'proper' IWI would extremely expensive and disruptive, and I'm worried about it causing condensation problems.

    Would affixing just thin insulated plasterboard (15mm celotex + 12.5mm plasterboard) to my external walls be a good idea? Calculator suggests that this would reduce the U-value from 1.1 to about 0.55. A decent improvement, and am I right that by not lowering the U-value by 'too much' I'd reduce the chance of condensation issues?

    Also, instead of removing the cornices, the insulation could just finish where the cornice starts. Given it would only encroach by an inch, I don't think it would be noticeable. I -might- even be able to get away without removing the skirting boards as they're quite thick. i.e. thin insulation would basically make it all a lot easier and cheaper to do.

    Of course, I'd end up with a strip at the top and bottom of walls which was un-insulated if I did this, so is it a stupid idea? Greatly appreciate any advice.
    • CommentAuthortony
    • CommentTimeDec 21st 2017
    That would not pass regs -- part L1b

    Re skirtings, likely no plaster behind them and LOTS of draughts
    • CommentAuthorGarethC
    • CommentTimeDec 22nd 2017
    Thanks Tony. Ah well back to the drawing board. Still searching for stuff I can do to my place that will make a meaningful difference without bankrupting me!
    IMHO from my own basic research as a newbie

    It should make some difference to how the room feels. Does the room feel cold or do you want to save heating costs

    From what i understand, the deeper the insulation the more condensation becomes an issue. 15mm is not much depth of insulation.

    I would be interested to hear any feedback on benefits if you did go ahead with this.
    Heave you run the costs ?

    94mm bullnose skirting is about £1.60 per metre and plaster coving can be under £1.50 per metre even from Wickes. That is probably quite a small amount if you are using pb with pir attached at £30 or so per metre run.
    • CommentAuthortony
    • CommentTimeDec 22nd 2017 edited
    Yea but it is probably fancy moulded plaster cornices and high skirtings
    • CommentAuthorGarethC
    • CommentTimeDec 22nd 2017
    Yes, unfortunately. Massive great (but very nice) ornate cornices and foot high skirtings.

    Basically I want to do anything I can, but the cost and hassle of 'full/proper' IWI my flat would be way too much for me. Plus, I'm essentially a flat, as my home is a big victorian villa split into three homes, one above and below ours, so I worry fully insulating our 'slice' might do weird things to condensation elsewhere.
    • CommentAuthormike7
    • CommentTimeDec 22nd 2017 edited
    Posted By: tonyThat would not pass regs -- part L1b

    I'm a real novice on this but just now I took a look at L1b, where sections 3.7, 3.8 and 3.9 seemed to offer a way round or exception for Gareth's situation. Can someone more familiar with these regs check it out?
    (I'd quote these paragraphs here except I can't seem to copy them out of the pdf :sad:)
    • CommentAuthorGarethC
    • CommentTimeDec 26th 2017
    Thanks for that Mike. Does seem like there are likely to be exemptions. That helped kick-start my brain, and what I really need to do is contact Historic Scotland for advice. They're only about a mile away from where I live, so might see if I can organise a face to face chat.
    • CommentAuthorCWatters
    • CommentTimeDec 26th 2017
    Doing what you propose would change the temperature profile through the wall. Eg if would make the inside of the wall colder than it is now. I think you would need to be careful not to create an interstitial condensation risk. That could be reduced,/eliminated by adding a vapour barrier on the inside but that would probably defeat the purpose of your proposal which I assume is minimum disruption.
    • CommentAuthorGarethC
    • CommentTimeDec 27th 2017
    Yes, that's the thing. I'm incredibly keen to upgrade the thermal performance of my conservation area home, but the cost and disruption of most IWI options are astronomical and I'm petrified of creating condensation problems. There's got to be -something- more that is sensible to do (already well draught-proofed). Hence wondered if just an inch of insulated plasterboard would provide quite an economical, but worthwhile thermally, improvement while still keeping the risk of condensation low. Any better ideas welcome! I can't be the only one in this situation.
    Posted By: GarethCI looked into injecting EPS beads between the studs behind my period lath and plaster wall,

    I thought that lath and plaster was confined to internal walls, surely external walls would have plaster (if it's old then lime with horse hair binder) straight on the brickwork.

    What is the wall construction that you have and do you know for sure - (I once had a house (now 200 years old) that had what looked like flemish bond walls but was actually a cavity wall with snapped headers to give the impression of a solid wall. It fooled the building society surveyor)
    • CommentTimeDec 27th 2017
    Posted By: Peter_in_HungaryI thought that lath and plaster was confined to internal walls, surely external walls would have plaster (if it's old then lime with horse hair binder) straight on the brickwork.

    You're assuming there IS brickwork. On the house next door to us, the lath and plaster is the external wall. Timber frame with infill lath and plaster was a common way of building. Only rich people could afford brick infill.
    • CommentAuthorGarethC
    • CommentTimeDec 27th 2017
    I cut a chunk out when fitting a TV wall bracket. Certainly seems to be lath and plaster on really thin studs. I - think - but can't recall with certainty, that it's then brick, rubble, then stone (ashlar).
    • CommentAuthortony
    • CommentTimeDec 27th 2017
    Probably seriously draughty in the void
    • CommentAuthorCWatters
    • CommentTimeDec 28th 2017
    The work involved in fitting 1" of insulated plasterboard is going to be similar to 2" or more.
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