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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorDen
    • CommentTimeMay 14th 2021
     
    Hello, I'm looking at options for IWI as part of a full house refurb for solid stone 50cm granite/whinstone walls (externally rendered). What I'd like to do is make good internal plaster/ parge coat as required with NHL lime/sand, then woodfibre insulation, then internal finish.

    I've been looking at (a lot of) different options and came across the warm batten method and thought I might be able to adapt as follows.
    1. External wall
    2. Internal Lime Parge Coat/Plaster
    3. 40-50mm Flex Wood Fibre Batts
    4. CLS 38x63 timber either screwed through Batts to masonary wall (might be tricky) or carefully framed so flex woodfiber just fits behind with tight fit against wall. The 63mm face would be parallel to wall.
    5. 40mm Flex Wood Fibre fully filled between CLS battens (assume the wood fibre can compress 2mm)
    6. Plasterboard (preferred) / Fermacell or Econic Board (shower rooms/kitchen) screwed to battens
    7. Breathable paint

    Does this sound ok? The flex woodfibre is much cheaper than the rigid boards and has marginally better thermal performance (0.038 vs 0.04)? Udireco, a flex woodfiber/rigid wood fiber sandwich designed to fix directly to masonry walls started me thinking this way. I havent worked out U-value for this but think it would be ~0.3-0.4 (I don't want the U-value to be too low, to allow some heat into the stone walls). I'd add a VCL behind the boards in the shower rooms.

    Thanks and any comments appreciated!
    Dennis
  1.  
    Whilst it doesn't answer your question, as it is rendered outside anyway have you considered EWI. This would be better for the walls.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 14th 2021
     
    The Udireco flex is cheaper as well as better thermal? That's surprising, gd news, as it's a game-changer for EWIing wobbly old rubble walls.

    Tho, from Back to Earth website, basic full-pallet price of 200 Udireco is £64.85/m2; 2x80 Uditherm + 40 UdiSpeed is £42.44, tho the latter, in three layers, prob costs more to fix. But still ...
    • CommentAuthorDen
    • CommentTimeMay 14th 2021
     
    Hi Peter, yes, but its not possible as the house is Cat C listed (Scotland) and the main element of the listing is how the external facade looks in relation to others in the terrace!

    The majority of articles I've read for IWI seem to suggest that woodfibre in direct contact with the wall is a good solution, but not to overinsulate the walls to reduce the risk for interstitial condensation
    • CommentAuthorDen
    • CommentTimeMay 14th 2021
     
    Hmm, maybe I've confused people. The Udireco looks nice, but its not cheap but it was more the principle of having a flexible wood fibre in direct contact with the wall which would help take up any small irregularities

    40mm Flex wood fibre ~£5/m2, CLS is £1.67/linear meter, and PB is ~£2.50/m2.
    So for layer of flex, battens over, flex between battens then PB works out ~£16/m2
  2.  
    Why not (a) rip the CLS down so it's 38 x 31.5 (x2)? You don't need it 63mm wide. It just takes up insulation space. And (b) possibly use 20mm rigid w/f/lime plas instead of plasterboard (except in the bathr, I accept)?

    You ought to be able to get your supplier to do a condensation risk analysis. If it's Back to Earth they will do a WUFI dynamic analysis which is much more accurate than the Glaser (B.S.) method.
    • CommentAuthorArtiglio
    • CommentTimeMay 15th 2021
     
    I’m in the process of insulating a property ( mix of internally rendered, brick and flint walls) i’m using a bonded system of woodfibre.
    Using Baumit RK70 to bond either Steico Therm or ProtecDry directly to the internal surface. Then mechanical fixing with ejotherm hammer in fixings. Depending on what the supplier can get i’m making the total thickness up from 20mm therm and 40 or 60mm protecdry as required. Once the first board is bonded any second board is just fixed with the ejotherm “nails”.
    So long as the wall is fairly flat ( you’ve dealt with that with the parge coat) its a fairly simple straight forward process. In my case the therm is square edged and the protectdry tongue and groove.
    I chose the steico products as there was the option to collect from the distribution depot ( only 30 miles from me) which saves the pallet delivery costs, combined withs discount for the quantities bought it made things less financially painful.
    Deciding on the levels to insulate to was one of the harder choices. One supplier wanted 120mm on all external walls and just about every internal void stuffed full of wood fibre. This would have created issues with room sizes and depths of window reveals etc. So after reading plenty of threads on here and other sites, opted for 60mm for the most part with 80mm on 1 wall as it helped get round a step in a wall. ( the decison was largely on gut feeling and aesthetics).
    The aim being to end up with a finished home that is comfortable to live in and reasonable economical to heat, its grade2 listed , but must be said the council have been pretty good (after lots of discussion), though i’m lucky in that the building has no real historical interest, has been thoroughly abused in its lifetime and was likely originally listed as much to stop it being pulled down as anything else. It’s also been through various adaptions and conversions so again there was some flexibility in the design. Initially the council were anti any insulation at all. This from a council that declared a “climate emergency” but in reality have done nothing about it.
    I had been pulling my hair out in respect of some damp patches on a couple of walls, but having dealt with gutters, leaks, poor pointing etc and not having solved them, realised it was warm moist outside air condensing on the cold internal surfaces ( place has been unheated for nearly 2 years, and takes forever to warm up or cool in response to outdoor temperatures. Worst location is a section of old solid floor in a corner of the building that otherwise has suspended wooden floors. MVHR is being installed, but this is really going to more of a way of dealing with ventilation issues than a pure heat recovery and airtightness goal. ( no double glazing allowed , existing joinery to remain much as it is ( though there will be some secondary glazing to keep worst of draughts down) it also gets around the need to punch holes through the walls for fan vents for the “wet areas”. Though must be said its an expensive and timeconsuming solution instead of half a dozen wall fans.
    • CommentAuthorkristeva
    • CommentTimeMay 15th 2021
     
    Posted By: DenHello, I'm looking at options for IWI as part of a full house refurb for solid stone 50cm granite/whinstone walls (externally rendered). What I'd like to do is make good internal plaster/ parge coat as required with NHL lime/sand, then woodfibre insulation, then internal finish.

    I've been looking at (a lot of) different options and came across the warm batten method and thought I might be able to adapt as follows.
    1. External wall
    2. Internal Lime Parge Coat/Plaster
    3. 40-50mm Flex Wood Fibre Batts
    4. CLS 38x63 timber either screwed through Batts to masonary wall (might be tricky) or carefully framed so flex woodfiber just fits behind with tight fit against wall. The 63mm face would be parallel to wall.
    5. 40mm Flex Wood Fibre fully filled between CLS battens (assume the wood fibre can compress 2mm)
    6. Plasterboard (preferred) / Fermacell or Econic Board (shower rooms/kitchen) screwed to battens
    7. Breathable paint

    Does this sound ok? The flex woodfibre is much cheaper than the rigid boards and has marginally better thermal performance (0.038 vs 0.04)? Udireco, a flex woodfiber/rigid wood fiber sandwich designed to fix directly to masonry walls started me thinking this way. I havent worked out U-value for this but think it would be ~0.3-0.4 (I don't want the U-value to be too low, to allow some heat into the stone walls). I'd add a VCL behind the boards in the shower rooms.

    Thanks and any comments appreciated!
    Dennis


    This may be a silly question Dennis, but what type of 'breathable' plasterboard to plan to use? I assume you're not using standard plasterboard.
    • CommentAuthorArtiglio
    • CommentTimeMay 15th 2021
     
    Dennis

    Apologies i missed your part about plasterboard, i’ve had baumit lime plasters applied direct to the woodfibre.
    •  
      CommentAuthordjh
    • CommentTimeMay 15th 2021
     
    Posted By: kristevaThis may be a silly question Dennis, but what type of 'breathable' plasterboard to plan to use? I assume you're not using standard plasterboard.

    Plasterboard is vapour permeable as long as it is paper-faced. A bit more so than lime plaster I believe. Both are vapour permeable. It's only foil-faced plasterboard that is not.
    • CommentAuthorDen
    • CommentTimeMay 15th 2021
     
    I'd read somewhere that standard paper backed plasterboard is still relatively vapour permeable, and it's usually the vcl behind/modern paints that reduce this. It's why I included as a potential option in the build up I've suggested (but not for bathroom/kitchen). Thanks for the tip on timber widths, Nick. The house is 5mins from a sawmill/builders merchants so I'm sure they could do this for me. Artiglio, your house sounds almost identical! Empty for 2 years, leaks in roof, blocked gutters, drains, and no original features inside! I'd originally assumed 60mm hard steico+lime internal plaster. I've lime rendered externally in the past (more rustic finish), but with all the rest of the work I'll end up doing trying to see if this could be an option to save some time (and cost)...
  3.  
    I may just be a grumpy g*t in my dislike of gypsum, but a lot of experience shows that it tends to 'support' mould rather better than lime (not that lime is 'without stain' - I've got some irritating mould growth on lime in my cellar). Yes, I realise mould should be unlikely inboard of insulation, but there is still the possibility at thermal bridges such as wall junctions and window reveals where the thermal bridge is not mitigated. In those circs I think I would rather have lime than plasterboard.

    I agree time is an issue for lime vs plasterboard, but the Baumit plasters particularly are so easy to 'learn' that I can get a good-excellent finish with them, and I am rubbish with Thistle etc. Yes the process from start to finish is slow, but if you have other areas to work on too you can keep it going without having to stop and watch plaster dry!
    •  
      CommentAuthordjh
    • CommentTimeMay 15th 2021
     
    Posted By: Nick ParsonsI may just be a grumpy g*t in my dislike of gypsum, but a lot of experience shows that it tends to 'support' mould rather better than lime (not that lime is 'without stain' - I've got some irritating mould growth on lime in my cellar)

    I'd agree that lime is more mould resistant, but that's more due to the good properties of lime (it's strongly alkaline) rather than any bad properties of gypsum. And some of its reputation is earned historically from its use in animal sheds, where the benefit was achieved by applying a fresh coat of limewash every year. Not something that's likely to be applied domestically.

    The key to preventing mould is reducing humidity and active ventilation is the best way to do that.
    • CommentAuthorkristeva
    • CommentTimeMay 16th 2021
     
    Posted By: djh
    Posted By: kristevaThis may be a silly question Dennis, but what type of 'breathable' plasterboard to plan to use? I assume you're not using standard plasterboard.

    Plasterboard is vapour permeable as long as it is paper-faced. A bit more so than lime plaster I believe. Both are vapour permeable. It's only foil-faced plasterboard that is not.


    I didn't realise this, thanks.
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