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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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    • CommentAuthorbogal2
    • CommentTimeSep 9th 2015
     
    Just discovered that Diffutherm, pavatex has come down in price since their new factory near Paris. I've had a figure of £47/m2 for a 200mm EWI system with a 140 mm board and a 60mm board with six fixings per board. This would seem to have a combined lambda value of 0.044, although the company selling this don't seem to be able to work this out themselves!! The boards individually are 0.038 and 0.043 for the thinner one, shame you can't glue the boards together. I might struggle to get PAssivhaus certification though.
    Not as good as a lambda of 0.031 with graphite EPS but no shower of EPS every time you cut it with a saw, I know you can get a hot knife but the fitters I've talked to don't use them. Also no issues with disposal in the future. I've read on hear that EPS is the most eco friendly option for fossil fuel insulation but not sure why.
    Was going to have a go at fitting the woodfibre myself if I choose this option, anyone any experience? XPS apparently below dpc to foundation.
    • CommentAuthortony
    • CommentTimeSep 9th 2015
     
    EPS every time. Breathable (xps does not). Anything that can biodegrade is not an option for me.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 9th 2015
     
    Interesting about woodfibre price - on the continent it's almost the cheap option.

    Agree with tony - and EPS is fine below DPC too -

    doesn't degrade with water
    even when saturated (standing water) still retains 75% of its insulativeness
    when merely wet loses almost no insulativeness,
    and yes it lets water in but lets it drain out and dry again
    whereas closed-cell insulations like XPS are supposedly waterproof but actually gradually take up water into the cells, never to dry out again.

    For cutting EPS, something like
    http://www.ebay.co.uk/itm/Polystyrene-cutter-EASYCUTTER-1-350-mm-styrofoam-cutter-hot-wire-foam-cutter-/221476355851?hash=item339104ff0b
    is a no-brainer
  1.  
    Was demonstrating different renders and finishes at CAT last week, and decided, after an unscientific 'nose test' that I do like lime so much more than nostril-stripping synthetic finishes. I am not sure I could take dong a whole wall/house in the smelly synthetic stuff.
    • CommentAuthorSaint
    • CommentTimeSep 9th 2015
     
    Posted By: fostertomwhereas closed-cell insulations like XPS are supposedly waterproof but actually gradually take up water into the cells, never to dry out again.


    XPS was originally invented to be used as a flotation billet so not taking up water would be an important design parameter.
    It can under certain conditions be made to take up moisture by diffusion but in conditions typically only created in labs. It doesn't pick up moisture by absorption
  2.  
    Both EPS and XPS manufacturers love to go at each other and produce papers showing how their product is far better and the ticking timebomb of the opposition. You can find lots of information either way online, XPS has been used (and certificated in such ways) successfully below DPC for many decades and is physically tougher and less likely to mechanical damage. If you let XPS get wet like EPS it dries out again, its not a one way valve.

    I have used both EPS and XPS below DPC in different areas on my house - walls XPS, under slab EPS.
    •  
      CommentAuthordjh
    • CommentTimeSep 9th 2015
     
    Posted By: bogal2no shower of EPS every time you cut it with a saw

    Woodfibre is much worse than EPS when you cut it. Definitely a good idea to wear a mask, there's loads of dust fibres come off of it. Cutting EPS is annoying, but not irritating to me, unlike both woodfibre and mineral wool.
  3.  
    ''Woodfibre is much worse than EPS when you cut it. Definitely a good idea to wear a mask, there's loads of dust fibres come off of it. Cutting EPS is annoying, but not irritating to me, unlike both woodfibre and mineral wool.''

    Agree with that! Cutting outside, we left the client's car looking like it was 'flocked'! Dust mask definitely required.
    • CommentAuthorbogal2
    • CommentTimeSep 9th 2015
     
    Hi Nick, glad to hear you finally managed to get someone to use woodfibre! How will EPS be disposed of in the future I wonder? If I go for EPS will definitely get one of those hot wires, thanks Tom. Just had an update on the point thermal bridging from the company which makes the lambda value for the 200mm woodfibre combo with fixings nearer 0.04.
  4.  
    •  
      CommentAuthorfostertom
    • CommentTimeSep 10th 2015 edited
     
    Seems a lot of money for a hand-held thing that can't be precision-set, like others for similar money can.

    And don't pay £19.99 for lo-grade replacement cutting wires - make your own up from hi-grade lengths from e.g. v helpful tommander@alloywire.com
    • CommentAuthorwookey
    • CommentTimeJan 6th 2019 edited
     
    Bogal2. Which did you pick in the end?

    I've also noticed that woodfibre is a lot less extortionate than it used to be and the U-value isn't much worse than platinum EPS so I'm considering using it. Main advantage seems to me to be avoiding putting a load of plastic into the building for when it's eventually taken to bits.

    Pros:
    Natural material (good for lifecycle end, embodied emissions?)
    Cutting doesn't spread plastic.
    Better soundproofing
    More solid for fixings? (not sure about this)
    More vapour permeable

    Cons:
    More expensive
    Heavier to carry/transport/fit
    Will degrade if it gets soggy
    Harder to cut?
    Less conventional

    What did I forget?
    • CommentAuthortony
    • CommentTimeJan 6th 2019
     
    Organic insulation is not fail safe if it were to get wet or damp so for me is a non starter
  5.  
    Posted By: tonyOrganic insulation is not fail safe if it were to get wet or damp so for me is a non starter

    +1
    In addition EPS is much more of a known quantity with builders so getting quotes and builders to do the job should be easier - that is if you are not DIY
    • CommentAuthorowlman
    • CommentTimeJan 6th 2019
     
    Some Pavatex boards have increased water resistance, and if the job is done right water ingress shouldn't be a problem, and as you say it's not shoving a load of plastic into the environment.
  6.  
    Coming with no experience here, but isn't wood fibre supposed to be hygroscopic and the renders are supposed to be water vapour permeable?

    So the outside face of the wood fibre would be soaking up water vapour from the outside during damp weather.

    What happens to this water, does it soak through the wood fibre and evaporate into the house on the warm/dry inside face, assuming there's no vapour resisting layer on the inside? (Paint?) Or does it just soak the wood fibre until there is dry sunny weather and then evaporate back out to the outside again?

    Not saying this is necessarily a problem, presumably thatch and straw houses have worked like this for 100s of years.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 6th 2019 edited
     
    AFAIK all EWI renders are water vapour permeable. Yes water vapour does equilibriate through the render face.

    But water in vapour form is harmless - only a problem if/when it condenses to liquid. And even if that happens in the outermost layers of wood fibre, no problem as long as liquid water content %age remains below a certain level, and even then no problem as long as it re-evaporates fairly soon e.g. when the sun shines, or even at end of winter. Your wool jersey is very good at soaking up liquid water (your sweat) and storing it into the sacs that organic materials possess (that sac storage is called hygroscopicity) and re-evaporating it soon enough.

    So outermost layers of any kind of EWI condense and re-dry regularly. The problem arises when it gets wetter (higher %age content) or deeper in or for longer or permanently - then decomposition/swelling/rot likely begins.

    The worst thing to do is to try to 'keep it dry' via impermeable outermost layers - which will prob be more efficient at preventing re-evaporation that absolutely preventing any ingress. Which casts doubt on the so-called sealed-cell plastic insulations i.e. all of them except EPS.

    NB all of this says nothing about uptake of liquid water via leaks. The render may be permable to water vapour but is impermeable to liquid water. If it's discontinuous or not sealed to window frames/cills etc, then rain may get in and that's big trouble.
    •  
      CommentAuthordjh
    • CommentTimeJan 6th 2019 edited
     
    Posted By: WillInAberdeenSo the outside face of the wood fibre would be soaking up water vapour from the outside during damp weather.

    What happens to this water, does it soak through the wood fibre and evaporate into the house on the warm/dry inside face, assuming there's no vapour resisting layer on the inside? (Paint?) Or does it just soak the wood fibre until there is dry sunny weather and then evaporate back out to the outside again?

    Not saying this is necessarily a problem, presumably thatch and straw houses have worked like this for 100s of years.

    What Tom said.

    Thatch, yes for many 100s of years. Straw not so much; the first straw house was built about 100 years ago after the baler was invented, but in a fairly dry climate. Only one or two decades experience in the UK climate. But then the straw is protected from direct rainfall by a covering and by overhangs etc, so it has a much easier life than a straw or reed roof. Hence the need to replace roofs regularly.

    Posted By: fostertomNB all of this says nothing about uptake of liquid water via leaks. The render may be permable to water vapour but is impermeable to liquid water. If it's discontinuous or not sealed to window frames/cills etc, then rain may get in and that's big trouble.

    This is very true. Liquid water is hugely more dense than water vapour, so many more molecules pass through a crack if there is liquid than if there is just vapour. The general rule of thumb for straw is that it will recover from rain falling against its sides, but if rain gets into the top of a stack then it may well be game over. A good drain at the bottom is also important, so there is no chance of the straw being in standing water.

    I expect woodfibre behaves at least as well, particularly since it often contains additives like borates that protect against insects and rot to some degree. We have woodfibre in our window surrounds, since it can be cut to a more precise shape than a straw bale, so I for one trust it will perform OK.
    • CommentAuthorbogal2
    • CommentTimeJan 8th 2019
     
    I ended up using graphite EPS on my house. Just doing a new build commercial passivhaus and using Udispeed woodfibre boards with Baumit lime render on a twin wall timber construction. The plasterer thinks it's brilliant. It looks good too. For EWI retrofit in future I would be tempted to try I beams fixed to the walls, filled with Warmcel and either wood fibre rendered board or wooden cladding. Chris at Backtoearth insulation is a brilliant help with boards and render and has first hand experience of applying it.
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2019 edited
     
    Posted By: bogal2filled with Warmcel and either wood fibre rendered board or wooden cladding

    I think you'd want something more rigid than just a breather membrane over the muslin on the outside, otherwise the warmcel is likely to bulge so much it bridges the gap behind the cladding. So I think I'd go for some woodfibre board, or at least some exterior board of some kind before putting cladding over the top.

    edit: but I like the general concept :bigsmile:
    • CommentAuthornplusone
    • CommentTimeMar 11th 2019
     
    Bogal2 any advice on a wall structure for a new build using wood fibre boards externally and Warmcell filled TF studs? Scratching my head as to how best to get a decent thermal performance without spending a fortune.
    • CommentAuthortony
    • CommentTimeMar 11th 2019
     
    Eps externally and mineral quilt or batts between the studs

    Should set U value target first and aim at that, I go for 0.1
    • CommentAuthorbogal2
    • CommentTimeMar 31st 2019
     
    Ive just used Udi 40mm woodfibre boards and baumit render over a TFbuilding with Warmcel between twin wall studs. Chris bookman from Back to Earth is really helpful. Interestingly 40mm wood fibre boards are cheaper than cement boards, really wind tight, as T and G, and you get extra insulation.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 31st 2019
     
    Posted By: djhyou'd want something more rigid than just a breather membrane over the muslin on the outside
    The trick is to staple the scrim (muslin's something else isn't it?) not just to the outer-edge face of the studs, but also (or instead) 15mm back, to the side-faces of the studs. That gives space for the Warmcel to bulge a bit - but the scrim-filled Warmcel should be rollered back as well before fitting whatever goes over it.

    At any rate, the Warmcel should be blown in between two 'walls' of scrim before any facings are fitted inside or out, so full-fill can be visually checked and any xs bulges pushed back. There's an excellent video about it, that I've posted several times.
    •  
      CommentAuthordjh
    • CommentTimeMar 31st 2019
     
    Posted By: bogal2Ive just used Udi 40mm woodfibre boards and baumit render over a TFbuilding with Warmcel between twin wall studs.

    No ventilation gap? I'm not critical, just curious.
    • CommentAuthorbogal2
    • CommentTimeMar 31st 2019
     
    No ventilation gap. Shouldn't be needed.
    • CommentAuthorgravelld
    • CommentTimeMar 31st 2019
     
    Posted By: bogal2... For EWI retrofit in future I would be tempted to try I beams fixed to the walls, filled with Warmcel and either wood fibre rendered board or wooden cladding. Chris at Backtoearth insulation is a brilliant help with boards and render and has first hand experience of applying it.
    Are you referring to having experience of I Beam or Larsen truss retrofit?
    •  
      CommentAuthordjh
    • CommentTimeApr 1st 2019
     
    Posted By: bogal2No ventilation gap. Shouldn't be needed.

    Well, I agree since I have directly rendered bales. :) But it does contradict traditional thinking. Is there a BBA or whatever that recommends/supports the approach?
    • CommentAuthorbogal2
    • CommentTimeApr 6th 2019 edited
     
    I was just referring to his experience with woodfibre and render. Not sure about BBA approval I’m afraid.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2019
     
    In what way is this different from direct render on e.g. EPS EWI? which has always contradicted conventional wisdom about ventilation gap, behind the render.
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