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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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      CommentAuthorfostertom
    • CommentTimeJan 17th 2020
     
    What do we think are the safe and practicable limits on waviness of wall surface for application of EWI?

    The walls in question are rubble stone, cement spatterdash rendered in gd condition. Pics attached
      farmhouse1.JPG
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      CommentAuthorfostertom
    • CommentTimeJan 17th 2020
     
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      farmhouse2.JPG
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      CommentAuthorfostertom
    • CommentTimeJan 17th 2020
     
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      farmhouse3.JPG
  1.  
    V hard to tell from the pics, FT, but it does not look too wobbly to me. Full perimeter bead and cross-hatching at c 50mm thick looks like it should sort that. If a straight-edge across 2 high-spots yields a space under the straight edge of over 5-40mm then, in my view, 50mm 'sausage' not enough.
  2.  
  3.  
    Waviness should not be a problem - providing the waves are reasonably gentle. I've done a stone rubble wall (without render) and used a perimeter bead with 3 blobs in the middle of the board. IMO it is a waste to try to use the EWI to get a plumb and straight wall - go with the flow. I offered up the EPS first on doubtful bits to gauge the problem and hence the amount of adhesive to apply. On a couple of occasions, with projecting stones I had to gouge out the back of the EPS to make it practicable to fit. You will end up with edges and corners out of align but with a bit of care nothing that can't be resolved with an EPS rasp.

    I looked at the product at the above link and it would not be for me! To quote the product description

    The fixing creates a cavity behind the insulation board, which can then be adjusted post-installation to ensure the wall is level before further coats are applied.

    And

    Features & Benefits

    Provides a cavity behind the insulation board.

    IMO a cavity behind the EWI is the last thing you need - It provides an air path for convection to take away all the heat and could negate the benefits of the EWI
  4.  
    Have a look at Udireco - a mix of rigid and 'fluffy' wood-fibre. I did a bit of work on a house with this. The 'fluff' gives, allowing you to adjust each board on the (screw, not hammer) fixings. I liked it a lot. Luckily I was not paying for materials, but I gather it was quite pricey.
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      CommentAuthorfostertom
    • CommentTimeJan 17th 2020 edited
     
    Very interesting, all the Sto kit - so systematised, no doubt expensive, but prob v economic to a geared-up contractor.

    I'm not clear at what point the boards are offered up, after embedding the device(s) into the board. Looks like they're drilling thro the devices, with the board offered up. No fixing cement used?

    Cavity behind boards, if narrow e.g.19mm max as in DG, actually improve insulation, provided the cavity extends no more than say 1m2, so top-to-bottom or side-to-side air transport can't happen. Easy to ensure if using strips of fixing cement, but not if cement-less.

    Udireco - ea board = 1m2 and costs £52.80 @ 160thk - that's over half the £100/m2 (or less) guide price for complete EWI! Still, gd to know that soft/bendy boards are a possibility. The trick is the hard+(extra?)soft laminate? I wonder if some soft, perhaps non-building-industry layer of EPS cd be DIY-laminated to regular EPS, which is pretty rigid already. Say 35mm of soft with 150 hard.
  5.  
    ''Udireco - ea board = 1m2 and costs £52.80 @ 160thk - that's over half the £100/m2 (or less) guide price for complete EWI! ''

    Yes, but I think you will find that £100/m2 figure is (a) for 90mm graphite EPS, (b) totally unrealistic and (c) excluding all plumbing etc. alterations. I think we got to £160isdh for £150mm EPS, with everything.
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      CommentAuthorfostertom
    • CommentTimeJan 17th 2020
     
    Gd data Nick - thanks. Was that for 2 storey i.e. serious scaffolding? Wd bungalow save some of that? I guess the £160 doesn't include eave/verge extension?
  6.  
    No, FT, that was for a bungalow - minimal scaff. We didn't need to extend eaves ...just, and I allowed myself to convince myself to use proprietary alu verge extensions. Not a fan... But on the positive side (a) there was just enough undercloak to allow a less-vulnerable-than-usual seal to the verge trim and (b) it actually looks fairly OK. The 'ridge' capping detail just did not cut the mustard, though, and the in-line extension capping pieces were very basic. (trim providers may vary).
  7.  
    FT
    Having looked at the Sto-Rotofix details I can't see any mention of adhesive, and I can't see how adhesive could be used if, as quoted in the specs, "Allows for post-installation adjustment of the insulation." which IMO would not be possible if the EWI was glued in place.

    So my concern about having ventilation at the back of the EWI causing uncontrolled heat loss remains
    • CommentAuthorJeff B
    • CommentTimeJan 17th 2020
     
    <blockquote><cite>Posted By: Nick Parsons</cite>No, FT, that was for a bungalow - minimal scaff. We didn't need to extend eaves ...just, and I allowed myself to convince myself to use proprietary alu verge extensions. Not a fan... But on the positive side (a) there was just enough undercloak to allow a less-vulnerable-than-usual seal to the verge trim and (b) it actually looks fairly OK. The 'ridge' capping detail just did not cut the mustard, though, and the in-line extension capping pieces were very basic. (trim providers may vary).</blockquote>

    Any chance of any photo(s) of the alu verge extensions in situ?
    •  
      CommentAuthorfostertom
    • CommentTimeJan 18th 2020
     
    Posted By: Peter_in_Hungaryadhesive ... would not be possible if the EWI was glued in place
    Of course, that's right.
  8.  
    Posted By: Peter_in_Hungary
    So my concern about having ventilation at the back of the EWI causing uncontrolled heat loss remains


    Ensure the top/bottom rails and any aperture openings are sealed, normal practice anyway with EWI and rails/beads. No chance of it getting through the front mesh with multiple coats of render.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 18th 2020 edited
     
    With a wide-area cavity crosswise to the general direction of heat flow, it's not so much that cold air leaks into it from outside.

    Even if it's sealed tight from that POV, the cavity still acts as a route whereby heat can transfer from warmer parts of the cavity crosswise to colder or less well insulated parts. That's one of the several kinds of 'by-pass', which degrade overall performance - the less well insulated parts then get an increased proportion of the total heat traffic.

    So just having the cavity airtight from outside (and inside) isn't enough - the cavity has to be divided up into areas of about 1m2 max to limit the crosswise redistribution of heat.
  9.  
    I'm lost. The masonry will warm up with the addition of EWI - the mass of the masonry and the relatively small cavity where is exists - are you suggesting there will enough of an effect here to be measurable with say a FLIR camera?
    •  
      CommentAuthordjh
    • CommentTimeJan 18th 2020
     
    I believe Tom's right. If there is a large space (large X-Y dimension, but Z can be fairly small) behind the EWI, then convection cells can form and move heat from one place to another. So convection will move heat from hot spots on the outside of the masonry (or TF or whatever) and spread it around the inside surface of the EWI. That will slightly increase the temperature of the EWI and increase the overall heat loss.

    If anything I'd expect it to show on an IR picture as a more uniform surface, with reduced localised hotspots. I shouldn't think you can judge the change in heat loss from an IR picture itself - there are too many variables, I think and too small an effect.
  10.  
    Posted By: fostertomWith a wide-area cavity crosswise to the general direction of heat flow, it's not so much that cold air leaks into it from outside.

    Even if it's sealed tight from that POV, the cavity still acts as a route whereby heat can transfer from warmer parts of the cavity crosswise to colder or less well insulated parts. That's one of the several kinds of 'by-pass', which degrade overall performance - the less well insulated parts then get an increased proportion of the total heat traffic.

    So just having the cavity airtight from outside (and inside) isn't enough - the cavity has to be divided up into areas of about 1m2 max to limit the crosswise redistribution of heat.


    I guess a gap of up to 16mm is no problem as I thought that was the optimum gap in double glazing that is filled with air.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 19th 2020
     
    It's an optimum for that (glazing) purpose, where there's prob not much temp variation across the (fairly limited) pane area - tho in larger panes if the say 100mm wide perimeter strip could be invisibly compartmented from the centre-pane area, there might be less of this type of bypass loss.

    True that under such conditions convection is limited by a thin gap but would apparently set in above a certain gap width. But that wouldn't nec apply in a wide-area situation where there are significant temp gradients laterally (in addition to 'axially') to drive convection despite small-gap resistance.
  11.  
    No expertise, but as well as agreeing with Tom, I am wondering whether a gap between the wall and the EWI would

    1) allow rainwater to track down behind the EWI, say if it got in at the top, or underneath a window

    2) allow water vapour to permeate out of a warm part of the house wall (bathroom?) and track sideways until it found an unheated part of the house wall (loft?) to condense on

    3) allow fire to spread

    4) be home for mice or insects?
  12.  
    Going back to the pics in the OP, that's a lovely house and the waviness is part of the character. IMHO is better to reproduce the waviness in the EWI as PiH described, rather than use the EWI to 'straighten' it up as has happened to the roof?

    What are you going to do with the painted cement dash render, EWI over it or chip it off first?

    What are you going to do with the decorative chimney and breast to avoid cold bridging, and how will the top of the EWI join the roof verge and continue across the face of the chimney breast?

    Looking for pro tips for when we do our place!
    •  
      CommentAuthorfostertom
    • CommentTimeJan 19th 2020 edited
     
    Posted By: WillInAberdeenI am wondering whether a gap between the wall and the EWI would
    .....

    1) With or without such a cavity, if water's getting in it's a disaster, and hard to diagnose/locate. Indeed, around windows is the most likely fail point - but EWI is amazingly reliable, which is why the materials suppliers are generally relaxed about who installs it, offering a bit of on-site tech rep guidance to the tradesmen on ea job, if they haven't done it before. So get the detailing and workmanship right! If water gets in at the top, it's something grossly wrong with the roof. Cavity or not will neither help nor hinder, if there's failure.

    2) Dividing the cavity up into 1m2 areas prevents such tracking, and should easily be sealed from the loft.

    3) Such fire spread hardly arises with half-hour FR lo-rise - the EPS doesn't even need to be retardant; with hi-rise there shd be fire stops and all sorts of other precautions (at least post-Grenfell).

    4) Buildings have such cavities everywhere e.g. in conventional cavity walls riddled with entry points. We're surely especially carefully eliminating entries, for other reasons. And none of these cavities extending more than 1m2.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 19th 2020 edited
     
    Posted By: WillInAberdeenbetter to reproduce the waviness in the EWI, rather than use the EWI to 'straighten' it up as has happened to the roof
    Absolutely - actually the roof structure is prob 20C so pretty straight already. Shame it's already been re-covered - very nicely - creates a dilemma with extending eave/verge, especially as slate is so unadaptable.

    Posted By: WillInAberdeenpainted cement dash render, EWI over it or chip it off first?
    Keep - tho it's a bad idea on old walls because of likely moisture-impermeability (depending on the mortar mix), still spatterdash render generally isn’t bad – it forms micro-shrinkage-cracks all over, unlike smooth render which forms few cracks in larger ‘panels’. The latter swallow rain through the cracks but leave few pathways for re-evaporation, whereas the former, micro-cracking, allows lots of ways out, so mimics the true all-over permeability of lime render. So I’m not actually convinced that conventional-wisdom replacement of spatterdash cement render is in fact priority.

    On the other hand, if well adhered, spatterdash render forms an ideal surface for the cementitious gloop (like tile cement) by which EWI is attached. The only problem would be if at any stage plastic-based masonry paint has been used on the spatterdash, which might be the real impermeability problem. Investigation needed, then scabble or punctures thro it if nec.

    Posted By: WillInAberdeenchimney and breast to avoid cold bridging, and how will the top of the EWI join the roof verge and continue across the face of the chimney breast?
    Yeah, part of a complicated problem, requiring different combination of solutions almost every time. Made more difficult if, as here, it must be loft insulation at 1stfl ceiling level rather than EWI-like over the rafter tops.

    First thought is to EWI up the gable to extended verges, creating a new peak of roof capping the EWI, outboard of the stack - but DNPA Planners prob won't like that (I'd like, in fact, to create overhanging verges, eaves as well). That way, at least above the 'alcoves', the EWI wd link nicely with EWI-alike insulation over the rafter tops - but the hollow stack would punch up through that.

    But with loft insulation at ceiling level, EWI (but unfinished) is needed to the inside face of the gable and stack, within the loft, to link with the loft insulation. In that case, the thick 'alcove' gable-wall top surfaces, as well as the hollow stack, are uninsulated and cold will still strike down to affect the 1stFl room. Not ideal.

    Similar problem at eaves - if insulation over the rafter tops, all good. But if loft insulation at ceiling level, there's a hard-to treat (or even access) area on top of the wall - insulation here can at best be thin, poked down between the rafters. Hopefully it's got breather felt already.
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