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General: EWI and cavity walls ... not advisable?

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    • CommentAuthorscrimper
    • CommentTimeSep 18th 2013
     
    Thanks Tom, Richard & Saint .... have taken this all in, and have a meeting with the builder in question this afternoon to really thrash this out ... and also hopefully hack into some wall and find out what exactly is going on.

    ps. Saint ... does your figure of 0.29W/m2K for 100mm with Eco bead include the two courses of 100mm brick? Even if it doesn't, at least it is below the 0.3W/m2K so a good start!
    • CommentAuthorSaint
    • CommentTimeSep 18th 2013
     
    Scrimper, the quick calcs were done on a U value calculation program. In actual fact the internal masonry used was the program default of dense concrete block. I've just changed that to brickwork and the U value goes to 0.028W/m2K so even better!
    • CommentAuthordovecote
    • CommentTimeSep 18th 2013
     
    Scrimper

    For what it is worth I am sort of in a similar boat with a cavity wall and the need to upgrade the thermal performance - in my case to meet building regs (because I made significant changes to the wall).

    As Fostertom says it is well worth understanding the pros and cons and when I looked into it IWI came out badly with increased risk of condensation arising because it pulls the dew point inwards - where as EWI tends to push the dew point to the outside.

    My walls are a mix of solid, empty cavity and 1970s insulation foam fill. The EWI will have the added benefit of dealing with the solid walls, which are giant thermal bridges at the moment.

    Also, I now have a 'warm' roof, which caps off the cavities.

    That said, my EWI doesn't go on til the New Year so cant report on the outcome.
  4.  
    Saint, you may wish to remove a zero....!:bigsmile:
    • CommentAuthorSaint
    • CommentTimeSep 19th 2013 edited
     
    Posted By: Nick ParsonsSaint, you may wish to remove a zero....!:bigsmile:" alt=":bigsmile:" src="http:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" >
    Thanks Nick, well spotted. Spontaneous combustion would be an issue at that value :beard:
    It should read 0.28 W/m2K
    • CommentAuthorscrimper
    • CommentTimeSep 19th 2013
     
    Saint - 0.28 will still be an upgrade for us, for sure ... anyway, got a guy with an endoscope coming shortly to have a little peer around, should enlighten us a bit.

    Dovecote - great point about moving the condensation point inwards ... hadn't thought of that. Did you get any form of ECO grant for your EWI? Either way, would you mind sharing how much you have had to budget for it (per sq. m)? That would be a great help - thanks
    • CommentAuthordovecote
    • CommentTimeSep 19th 2013
     
    No grants were available to me and I haven't tried for a Green Deal either.

    Costs are in the region of £75 per square meter for 60mm phenolic based EWI - that was a quote from 12 months ago and did not include scaffolding.
    • CommentAuthorscrimper
    • CommentTimeOct 21st 2013
     
    Um ... hi all. So now we are two weeks into our build/renovation. All fine ... and we've discovered that a) there's not a shred of insulation in any wall in the whole house which is rather extraordinary and b) the cavities are crystal clear and a good 70-80mm wide ... so no reason you could possibly get away with calling them 'hard to fill' and managing to get a grant signed off.

    So - we've realized that forking out £20,000-£30,000 of our own moolah on EWI is a complete no-goer. Without a grant to help out, it would just be insanity. So we're left with the choice of IWI, cavity fill (or I guess at a stretch both). Now I'm a bit of a newbie to all of this (but learning fast I think), but my gut instinct is to go for the fill only option. We won't be subject to the kind of driving rain that might cause rising damp up the fill, and we really want to preserve as much internal space as possible. Very wary too of bringing the condensation point any further in than it needs to be ... which I gather can be the risk of IWI.

    Can anyone talk me out of taking the cavity fill option? And if you can't, could you tell me how on earth I find someone reputable out there to do the job ... someone who will hopefully be armed with some sort of thermal imaging camera and who can 'see' if there are any areas that have evaded the fill in any way? About half the house will need doing, so that's about 225sq metres, and I'm happy to pay relatively well for a job 'well done' ...

    Thanks all!
    • CommentAuthortony
    • CommentTimeOct 22nd 2013
     
    polystyrene beads and get platinum beads too and watch them like a hawk when the work is being done.
  10.  
    ''About half the house will need doing''

    What's the situation with the other half?

    I agree with Tony. Platinum EPS. hard to find people round here (Sheffield) who do EPS, and I suspect Platinum EPS would be even harder to find. I hope it's easier where you are. I have *never* heard of an installer who checks afterwards with IR camera. Yours could be the first! At least it's the right time of year. If you cannot get the installer to check with IR, you could borrow/hire one and get a comprehensive set of images and fwd them to the installer if any anomalies show up.
  11.  
    Hi,
    There is probably a good reason that IR cameras are not routinely used. You need a stable outdoor and indoor temperature for many hours if not days to get meaningful results. You also need a good temperature difference. My cavity filled bungalow does not need heating until outdoor temperature is below 10 C for some time. So even at this time of year very little heating is required. Also as solar heating can cause some heating of the external skin and wind direction can cause cooling. Also some one on this forum brought up the fact that the external walls near ground level were colder probably due to conduction into/out of the ground. From the houses I have had done it seems to come down to the operator and checking. If holes are drilled at 1 m centres and filling is blown in then it would be simple to check every hole has some fill before adding mortar and also the amount of insulation used is about right. If you can get to the cavity in the loft then you can check it has been filled. Also CIGA companies offer a 25 year guarantee - it may be useful to find out what this covers.

    Richard
    • CommentAuthorscrimper
    • CommentTimeOct 22nd 2013
     
    Great points - esp. about the IR camera being tricky to get useful info from. I guess we could make a pretty good calculation of how much material should be used up - but if it comes up short, it will be hard to know where it is missing from!

    Nick - the other 225sq m walls in the house will be new build, so will have standard insulation board in their cavities etc.

    I'm encouraged by what I hear so far - no one clouding the issue by waving their IWI banners!
    •  
      CommentAuthordjh
    • CommentTimeOct 22nd 2013 edited
     
    Posted By: scrimperthe IR camera being tricky to get useful info from

    Note that you can simply heat your house too much to increase the temperature difference. That doesn't get around the need for stable temperatures though.

    I guess we could make a pretty good calculation of how much material should be used up - but if it comes up short, it will be hard to know where it is missing from!

    I've heard that an advantage of Knauf Perimeter Plus over Warmcel is that the quantities injected are accurately measured and certified. I don't know whether the same might be true for their Supafil 34 for example. And I've no idea of the relative costs, especially for cavity insulation.
    • CommentAuthorTimSmall
    • CommentTimeOct 22nd 2013
     
    Also worth noting that cavity fill is likely to increase the humidity in the outer skin of the wall, and this will accelerate wall tie corrosion, so if in any doubt it's probably worth getting them replaced with stainless ties. Also, a USB endoscope is reasonably cheap - e.g. http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/641771.xml

    You might want to check for debris in the cavity near the base of the wall, and get a bricky to take out a brick or two to clear it if necessary.

    Also, sort out any dodgy pointing after the cavity fill has been done.

    Once you have the cavity filled, I'd take a look for leaks:

    http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=7396&page=5#Item_5
  15.  
    Just bumping this thread since it's 12 years later and I wondered what the forum's thoughts are on this topic today.

    A friend was asking about EWI vs IWI to a 1980's house which may have partial-fill cavity insulation. My kneejerk reaction was to say EWI every time, but I subsequently discovered some websites suggesting this would be a bad idea if the cavity is already full or partially full.

    Do we all agree? If so is that due to the dew point potentially arriving mid-way through the outer leaf and/or corroding wall ties? Or something else? Ventilation?
    • CommentAuthortony
    • CommentTimeFeb 21st 2025
     
    With EWI the dew point is almost certainly within the outside few millimetres of the external wall insulation.

    Partially filled cavities in my book = thermal bypass and so should be fully filled before EWI

    IWI will leave some thermal bridging at any internal partitions.

    I would go EWI every time
  17.  
    Posted By: tonyshould be fully filled before EWI


    Thanks tony, by what method? Remove the old batts somehow and re-fill or just blow new beads/cellulose into the remaining void?
    • CommentAuthortony
    • CommentTimeMar 8th 2025
     
    I like 200mm eps with modern render on mesh, cavity fully filled with eps beads
    •  
      CommentAuthordjh
    • CommentTimeMar 8th 2025
     
    Posted By: djhI've heard that an advantage of Knauf Perimeter Plus over Warmcel is that the quantities injected are accurately measured and certified.
    Since that time I built a house and used injected Warmcel in some parts (the roof especially) and I can now say that the quantities of Warmcel are accurately measured and certified too (I have the certificate).
  20.  
    What about a cavity that has been filled with wool batts? And has a 25mm airgap?

    Can you cavity fill the remaining 25mm with EPS bead?

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