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    • CommentAuthorandykent
    • CommentTimeFeb 9th 2012
     
    Both the EST and Celotex are recommending that internal insulation with rigid foam boards be done by fixing the insulation to the walls and then having battens and air gaps with plasterboard over. This surprises me, as surely that approach will both trap interstitial condensation and run the risk of convective loss if the air gaps aren't 100% sealed, negating the insulation? Interestingly, all the related text on both websites talks in terms of moisture from inside trying to get out - but fails to acknowledge the possibility of driving rain etc entering from outside.

    By way of an experiment, in late 2010 I fixed pieces of 75mm Celotex internally to a solid brick external wall in my house. Looking behind them recently, the paintwork has badly blistered and the walls get Protimeter readings in the 200s-300s (i.e. in the red area = unacceptably damp). Moisture that would previously have been driven back by heat loss is staying in the wall.

    Can someone explain to me the rationale behind the EST/Celotex advice, as I would have expected to do the reverse, i.e. air gap between insulation and masonry? The latter would allow condensation from outside to run down the internal masonry surface (or better still ventilate the air gap??) and keep the thermal envelope airtight.

    Of course the sensible approach might simply be to forget all about Celotex-type insulants and go for a breathable material instead, but can we focus on the Celotex-type approach for now. Before discounting their approach I'd like to understand the thinking behind it.
    • CommentAuthorShevek
    • CommentTimeFeb 9th 2012 edited
     
    I'm interested in this too.

    Kingspan follow your approach, with the battens fixed direct to brickwork over a DPC:
    http://www.kingspaninsulation.co.uk/Products/Kooltherm/Kooltherm-K18-Insulated-Plasterboard/Overview.aspx
    http://www.kingspaninsulation.co.uk/getattachment/39da3ae9-8f6c-4b8e-9220-7ae813d51603/Kooltherm-K18-Insulated-Plasterboard.aspx

    I'm hoping to deal with this issue on a loft conversion raised party wall by rendering externally.

    Where's EST's advice/details?

    Here's Celotex's relevant page (and their PDFs attached):
    http://www.celotex.co.uk/applications/refurbishment/internal-solid-walls
    • CommentAuthorpmagowan
    • CommentTimeFeb 9th 2012
     
    How do you ventilate behind the insulation and still keep airtight?
    • CommentAuthorandykent
    • CommentTimeFeb 9th 2012 edited
     
    @Shevek, from your links it looks like the more recent thinking is indeed to have the air gap on the outside of the insulation (e.g. around dabs). Interesting that the Celotex docs you attached show opposite approaches - the first link (June 2011) air gap inside, the second one (Jan 2012) air gap outside. So it seems the approach has evolved.

    I sit corrected on the EST advice, or at least what I could find just now. The following page is rather vague and seems to assume only internal-to-external moisture flow, whereas the document CE17 it mentions actually shows no air gap at all. Given the outcome of my own makeshift test this seems like a Bad Idea.

    http://www.energysavingtrust.org.uk/In-your-home/Roofs-floors-walls-and-windows/Solid-wall-insulation/Choosing-internal-wall-insulation

    Furthermore, recent research suggests that a perforation the size of a pinprick in a VCL allows 50% of the moisture to pass through, so I'm surprised all the sources this thread has looked at so far place such a heavy reliance on VCLs. Unless someone can post something we've missed.

    I would also be very interested to see if anyone can find any advice on whether to ventilate the air gaps.

    @pmagowan, the thinking is that the innermost layer of any surface is the thermal envelope, so it's that rather than any outer layer that needs to be kept airtight. In fact, the more airflow throw layers outside the insulation the better. Feel free to disagree anyone.

    Oh and of course all of the above assumes you're happy with thermally light external walls. Which depends on all sorts of factors like heating profiles and occupancy patterns.
    • CommentAuthorShevek
    • CommentTimeFeb 9th 2012
     
    Regarding the different Celotex details I'm not sure the dates are relevant, rather the different types of insulation they're using.
    • CommentAuthorandykent
    • CommentTimeFeb 9th 2012
     
    Ah OK, how so?
  1.  
    <blockquote><cite>Posted By: andykent</cite>Both the EST and Celotex are recommending that internal insulation with rigid foam boards be done by fixing the insulation to the walls and then having battens and air gaps with plasterboard over. This surprises me, as surely that approach will both trap interstitial condensation and run the risk of convective loss if the air gaps aren't 100% sealed, negating the insulation? Interestingly, all the related text on both websites talks in terms of moisture from inside trying to get out - but fails to acknowledge the possibility of driving rain etc entering from outside.

    By way of an experiment, in late 2010 I fixed pieces of 75mm Celotex internally to a solid brick external wall in my house. Looking behind them recently, the paintwork has badly blistered and the walls get Protimeter readings in the 200s-300s (i.e. in the red area = unacceptably damp). Moisture that would previously have been driven back by heat loss is staying in the wall.

    Can someone explain to me the rationale behind the EST/Celotex advice, as I would have expected to do the reverse, i.e. air gap between insulation and masonry? The latter would allow condensation from outside to run down the internal masonry surface (or better still ventilate the air gap??) and keep the thermal envelope airtight.

    Of course the sensible approach might simply be to forget all about Celotex-type insulants and go for a breathable material instead, but can we focus on the Celotex-type approach for now. Before discounting their approach I'd like to understand the thinking behind it.</blockquote>

    Hi Andy, I'm also very interested in this. Have you read the Joe Little articles linked to here? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6573&page=1

    I've been looking for evidence which supports the theroretical modelling done by Little as most seem to believe that the risk of interstitial condensation is low.

    His approach isn't the same as the EST details. How close did you follow their detailing?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 12th 2012
     
    Posted By: Mike GeorgeI've been looking for evidence which supports the theroretical modelling done by Little as most seem to believe that the risk of interstitial condensation is low.

    I am sure we could think up a way to test it easily and cheaply.
  2.  
    I'm all ears :bigsmile:

    My thoughts until now are that the only way to be sure is to find something upgraded at least a few years ago to a u-value better than say 0.5W/m2K. Even better if its lower than say 0.3W/m2K.

    Then all we have to do is open up an area and see whats behind it
    • CommentAuthorEd Davies
    • CommentTimeFeb 12th 2012
     
    Posted By: andykentBy way of an experiment, in late 2010 I fixed pieces of 75mm Celotex internally to a solid brick external wall in my house.


    Did you cover the whole wall or just small parts? The way that's worded makes me wonder.
    • CommentAuthorandykent
    • CommentTimeFeb 13th 2012
     
    It is the whole of one wall, approx 3.5m long x 2.3m high.

    Protimeter readings from other parts of the house suggest I'm going to have even more fun once I try to do the front wall, where in patches the readings go over 900. I think the stone here might itself be moisture permeable, as most of the pointing has been renewed.

    In any event, not something I would wish to leave an impermeable insulant in contact with for any length of time.
  3.  
    We're going with IQ-Therm insulation, which I'm hoping will provide the best of both worlds, being a breathable insulation but with decent u values without being a foot thick.

    http://www.interiorinsulation.co.uk/products

    The product is a PUR board with a series of regular holes filled with a mineral that allows the board to breath (I think it's the same mineral as used in Calsitherm, which was the other option I was considering, but which has poorer U values).

    We're looking to use an 80mm board that will hit building regs but still allow our solid walls to breathe.
  4.  
    If you need Internal Wall Insulation we are the company that supply the product, we can also get grants to lower the cost of fitment and product. It is ofgem approved and part of the Green Deal so where it cost full money to fit other brands of insulation we can lower your costs



    Contact me on 0845 402 3585
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 2nd 2012
     
    Mr Stokes, did you read the rules about advertising on here?
    •  
      CommentAuthorDamonHD
    • CommentTimeApr 2nd 2012
     
    Indeed, please edit out your contact details: don't SPAM us.
    • CommentAuthorwookey
    • CommentTimeApr 3rd 2012
     
    Andykent. Did you seal round your boards in what you believed to be an airtight way? Obviously if any air can get in it is likely to condense on the outside wall. I don't like ventilation behind insulation because it can move significant amounts of heat away. Insulation against still air is a better insulant overall than insulation against moving air, which can quite efficiently move the heat away (if there is enough air movement to remove water vapour).

    I've had 50mm PUR leaning up against my external garage wall (225mm brick) for the last few months, which has a breathable membrance (roofing membrane) attached to it (not in a very airtight way). The boards are not attached at all with big gaps behind, but the membrane has got quite damp, even wet, on cold nights behind the apex. It's very hards to tell if damp is coming from inside or outside, but I presume it condensation on the inside. So that even this mediocre insulation (with no air barrier on inside) is sufficient to cause condensation even in an unheated room. I'm just now attaching them properly and intend to embed a humidistat to see what it's like after it's all carefully sealed up. Of course there may not be enough cold nights left this year to get any numbers.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 3rd 2012
     
    Posted By: wookeyOf course there may not be enough cold nights left this year to get any numbers.

    There probably will be enough days, but anyway it will show the trend and you can easily extrapolate from that. Your in the East where the RH is lower than the West so your dewpoint temperature will be lower than mine for any given day.

    (Ambient RH/ Ambient Temperature) / (Wall RH/ Wall Temperature) should show the trend nicely.

    May try the same thing in my loft.
    • CommentAuthorJoiner
    • CommentTimeApr 3rd 2012
     
    Why is Mr Solid Wall's post still on here?

    And Steamy, he probably did read the rules but failed to understand them. Mind you, the clue why is in his username. Solid = thick! :devil:
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 3rd 2012
     
    As in Dense :cool:
    •  
      CommentAuthorJSHarris
    • CommentTimeApr 3rd 2012
     
    I keep a list of all companies that spam the ebuild forum (which, it has to be said, gets a fair bit of input from tossers like our thick friend here).

    As I'm in the market for a fair bit of house build related stuff I keep the list purely as a "remember never to do business with these scumbags" reminder, as if they feel it's OK to use forums to deceive people then in my view they won't have any qualms about deceiving customers. Best never to think of doing business with folk like this, in my view.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 3rd 2012
     
    Jeremy
    Don't mince your words, say what you really think :bigsmile:
    •  
      CommentAuthorJSHarris
    • CommentTimeApr 3rd 2012
     
    <blockquote><cite>Posted By: SteamyTea</cite>Jeremy
    Don't mince your words, say what you really think</blockquote>

    I do try.........
    • CommentAuthormartin.n
    • CommentTimeApr 6th 2012 edited
     
    Hi Andy.
    Nice to see that Celotex have caught up with the method I have been using since 2004. I adopted it because it means that if there is condensation between the insulation and the wall at least the battens are warm and dry. Incidental benefits are that the separate plasterboard is easily screwed onto the battens, and any fittings such as curtain rails or kitchen units can be screwed on to battens suitably placed, larger battens if nec; I then put 25mm of further insulation between the battens, or where desired run services between them.
    I seal the insualtion as well as poss, and any moisture which does get from room to behind the insulation is supposed to evaporate out thru the brick. An air gap achieves nothing as the route out for moisture is through the brick. I would worry if I had non permeable render. In areas of normal exposure this should be fine; in very exposed areas evaporation out through the brick might be too slow, or negative, at times.
    The idea is that the rate of air/moisture escape from behind the insualtion should be several times the rate of flow of warm moist air from room to behind insualtion, so i attempt a complete seal from room to behind insulation, but if a modest amount of moist air gets through it can easily evaporate to outside.
    To make the seal I use aluminium tape to attach insulation boards to each other, and all around the perimeter I leave a gap enough to get in the nozzle of an expanding foam gun and fill the full depth of the gap. this cos the tape does not adhere that well to old surfaces, tho it really grips the new foil surface of the boards.
    Moisture getting in from outside is not usually a problem as it evaporates back out again in areas of normal exposure. I have no experience in areas of very high exposure, but I like the idea of ventilated slate or timber cladding.
    • CommentAuthorGaryB
    • CommentTimeApr 6th 2012
     
    According to Builddesk's condensation analysis it doesn't matter if the insulation is fixed directly to the solid wall or via battens with a cavity between.

    As long as there is a VCL somewhere on the room side of the insulation (which could be the foil facing on the board) there are no interstitial condensation issues. Take away the VCL or perforate it extensively and the red warning notices for interstitial condensation / component failure start to appear in the calcs.
  5.  
    Yes, but beware that you generally get a 'pass' on a condensation risk analysis *because you have a 100% effective VCL*. Very few installed VCLs, in refurb particularly, are anywhere near 100% effective.
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