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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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  1.  
    At risk of repeating others, it depends a huge amount on the particular wall, and the location. A cement-pointed west-facing wall in Bristol is a totally different proposition from a south-facing stone-and-lime wall in Sussex. The key factors are how much rain penetrates in and how easily can it dry out.

    The various guides are helpful but if they are to be applied widely then they have to be very cautious. The effect of this caution is that many walls have remained uninsulated or poorly insulated, which could have been easily well-insulated. The building trade (including expert guidance) are naturally cautious because they carry the risk if there is damp, whereas the householder and the planet carry the risk if there is insufficient insulation.
  2.  
    Posted By: Nick ParsonsThe 'Bristolian's guide...' is good, but IIRC the author is fairly dogmatic that 60mm WF should not be exceeded. Other opinions exist. I usually used 100mm Pavadentro (with its 'mineral functional layer') when it was available, but do your homework. 60mm would be 'safe', I think, in most situations (on the right sort of substrates, of course), but be prepared to stand your ground when BCO is looking for 0.3W/m2K. (The 'get-outs' are in AD L1B)


    Nick, thanks for that, I’ve seen a post regarding the building regs clause on limiting thickness that needs to be cited for building control purposes. And I’ve heard you speak favourably about Pavadentro before. What do use now that it’s discontinued?
  3.  
    Posted By: WillInAberdeenAt risk of repeating others, it depends a huge amount on the particular wall.

    The various guides are helpful but if they are to be applied widely then they have to be very cautious.


    Good point. I almost shelved my IWI project completely following some of the guidance I’ve read
    • CommentAuthorbxman
    • CommentTimeJan 5th 2021
     
    you might learn something from spending 30 mins watching this who knows ?

    https://www.youtube.com/watch?v=UYTbMi2Jgfk&feature=emb_rel_end
  4.  
    <blockquote><cite>Posted By: bxman</cite>you might learn something from spending 30 mins watching this who knows ?

    <a href="https://www.youtube.com/watch?v=UYTbMi2Jgfk&feature=emb_rel_end" rel="nofollow">https://www.youtube.com/watch?v=UYTbMi2Jgfk&feature=emb_rel_end</a></blockquote>

    That video was one of the first things that switched me on to the benefits of IWI - and to highlight the risks of condensation. If you scroll through the comments he says there’s a problem with condensation forming on the electrical socket back boxes in one of the insulated rooms
    • CommentAuthordaveking66
    • CommentTimeJan 16th 2021 edited
     
    Posted By: Daveking66 the Steico supplier (Ecomerchant) has advised that their boards should be covered with a layer of waterproof plasterboard if used in a bathroom -


    Good news, two suppliers (Unity Lime and Mike Wye) have now advised that I won’t need to add a layer
    water resistant plasterboard in the bathroom.

    There’s obviously a risk I’m listening just to the advice I want to hear, but the addition of a water
    resistant Layer of board (to prevent ingress of water moisture) seemed to defeat the whole
    purpose of a breathable system.

    Just need to find a system for insulating the pitched section of ceiling now! (which I’ve raised in another post). Thanks for all your comments
  5.  
    If they are happy and the walls are not (and are never) going to be covered in impervious coatings/sheets then go with their view. They are both reliable sources. NBT used to do 'free' (you paid for it in the material price, of course) WUFI (interstitial condensation) calcs, which were v useful. I don't know of any supplier which does these now, and if anyone tells me of one I will probably use them!!
    • CommentAuthorJeff B
    • CommentTimeJan 17th 2021
     
    Posted By: Nick ParsonsIf they are happy and the walls are not (and are never) going to be covered in impervious coatings/sheets then go with their view. They are both reliable sources. NBT used to do 'free' (you paid for it in the material price, of course) WUFI (interstitial condensation) calcs, which were v useful. I don't know of any supplier which does these now, and if anyone tells me of one I will probably use them!!


    The Celotex technical department did a free condensation analysis for me. This was for a different set up though - IWI using PIR onto a cavity wall in which the cavity is filled with Rockwool fibre.
    • CommentAuthordaveking66
    • CommentTimeJan 23rd 2021 edited
     
    Very useful to know - thanks
    • CommentAuthordaveking66
    • CommentTimeFeb 15th 2021
     
    Posted By: Nick ParsonsThe 'Bristolian's guide...' is good, but IIRC the author is fairly dogmatic that 60mm WF should not be exceeded. Other opinions exist. I usually used 100mm Pavadentro (with its 'mineral functional layer') when it was available, but do your homework. 60mm would be 'safe', I think, in most situations (on the right sort of substrates, of course), but be prepared to stand your ground when BCO is looking for 0.3W/m2K. (The 'get-outs' are in AD L1B)


    Can anyone advise which part of the L1B regulations will help me fight my corner in regard to the application of a thinner layer of insulation to reduce condensation risks in a solid brick walled Victorian property? Nothing jumps out at me so far
  6.  
    General Guidance, sections 3.8 - 3.10, page 8. Annoyingly I cannot cut and paste from a pdf. Seems pretty unequivocal.
    •  
      CommentAuthordjh
    • CommentTimeFeb 17th 2021
     
    Works for me: :cool:

    "Historic and traditional buildings where
    special considerations may apply

    "3.8 There are three further classes of buildings
    where special considerations in making reasonable
    provision for the conservation of fuel or power
    may apply:
    a. buildings which are of architectural and
    historical interest and which are referred to as
    a material consideration in a local authority’s
    development plan or local development
    framework;
    b. buildings which are of architectural and
    historical interest within national parks, areas
    of outstanding natural beauty, registered
    historic parks and gardens, registered
    battlefields, the curtilages of scheduled
    ancient monuments, and world heritage sites;
    c. buildings of traditional construction with
    permeable fabric that both absorbs and
    readily allows the evaporation of moisture.

    "3.9 When undertaking work on or in
    connection with a building that falls within one
    of the classes listed above, the aim should be to
    improve energy efficiency as far as is reasonably
    practicable. The work should not prejudice the
    character of the host building or increase the risk
    of long-term deterioration of the building fabric
    or fittings.

    "3.10 The guidance given by English Heritage 3
    should be taken into account in determining
    appropriate energy performance standards for
    building work in historic buildings.
    In addition English Heritage has produced detailed
    technical guidance on how to implement specific
    energy efficiency measures. (See list of available
    guidance documents at http://www.english-
    heritage.org.uk/professional/advice/advice-by-
    topic/climate-change/energy-efficiency/.)"
  7.  
    Thanks @djh!

    Wonder why it won't let me copy and paste?

    It seems to me that the particular risk is that your BCO does not agree with you when you invoke the clause in 3.9:

    "3.9 When undertaking work on or in
    connection with a building that falls within one
    of the classes listed above, the aim should be to
    improve energy efficiency as far as is reasonably
    practicable. The work should not prejudice the
    character of the host building or increase the risk
    of long-term deterioration of the building fabric
    or fittings.

    If the BCO maintains that, for example, IWI with PIR will *not* ''increase the risk
    of long-term deterioration of the building fabric
    or fittings'' then you may be at stalemate.
  8.  
    Unfortunately the building regs and the "guidance given by English Heritage" are quite subjective, lots of phrases like 'reasonably practical” but nowhere does it say XX W/m2K. This for the reasons mentioned at the top of this page.

    Something official-looking from an insulation supplier might be what you are looking for, but remember that Victorian properties can be retrofitted to BReg standards, so the building control people might have a good point?
    Eg https://research.historicengland.org.uk/Report.aspx?i=15746
    • CommentAuthordaveking66
    • CommentTimeFeb 18th 2021
     
    Thanks all,

    Let’s see what they have to say about those clauses. My references to the advice in the Bristolian report have so far fallen on deaf ears though.

    That historic England report is interesting, thanks for sharing. Could anyone see where the results of the condensation monitoring are held? I could only see results for thermal performance improvements
  9.  
    https://buildingconservation.com/books/retrofit2017/files/assets/common/downloads/publication.pdf

    Brief mention on page 8:

    Moisture monitoring at New Bolsover
    has been carried out continuously
    since 2011. During this period seasonal
    fluctuations have been observed, with
    walls becoming wetter in winter and
    drying out during the summer months.
    So far, no conclusive evidence of moisture
    accumulation behind either insulation
    system has been observed, but monitoring
    is continuing
  10.  
    Also here

    https://historicengland.org.uk/whats-new/research/back-issues/simulation-models-and-energy-efficiency-in-historic-buildings/

    the performance of the two insulation systems [PIR and woodfibre] are similar
    with defined seasonal cycles - high relative humidities in the winter and drier in the summer
    there are incremental increases in relative humidities year-on-year, which implies that moisture is accumulating at the wall-insulation interface, although we have not observed any signs of condensation or mould nor any reduction in thermal performance. This suggests that, if conditions at the wall-insulation interface are allowed to drop to lower relative humidities during the summer months, the insulation systems will recover sufficiently to manage the higher levels during the winter

    there are clear influences of the climate (in particular, solar radiation), orientation, exposure and degree of shading. The west elevation which is exposed to the sun is performing better than the south elevation which is relatively sheltered
    • CommentAuthordaveking66
    • CommentTimeFeb 21st 2021
     
    WillnAberdeen Cheers for digging those out and pasting up. Much appreciated.

    Quite a marked difference in the findings of those reports. I was surprised they found no differences in condensation build up in the walls treated with PIR and those treated with wood fibre board in the New Bolsover end of Terrace Victorian House in the Historic England report.

    I found myself wondering if I’d backed the wrong horse, favouring woodfibre insulation, until I read the building conservation report,
    page 23, internally insulated walls, which compares a building insulated with 40mm of woodfibre board (Shrewsbury) and one insulated with 100mm PIR (Drewsteignton)

    https://buildingconservation.com/books/retrofit2017/files/assets/common/downloads/publication.pdf

    Maybe I’m listening to what I want to hear, and although there are a number of factors at play in terms of wall type and aspect, the big takeaway for me is the conclusion:

    “In conclusion, we find that the performance of these walls is in part conditioned by their individual material components, including changes made to the fabric to improve energy efficiency. Interstitial condensation has been a particular concern, yet the internally insulated brick wall at Shrewsbury, which uses a limited quantity of insulation and does not incorporate a VCL, has stable vapour responses that operate within safe limits. In contrast, at Drewsteignton, where insulation has reduced the U-value of the wall to a fraction of its previous heat loss and a VCL limits the movement of vapour towards the internal side of the wall, vapour conditions are deteriorating.”
    • CommentAuthorArtiglio
    • CommentTimeFeb 22nd 2021
     
    I’m not great with the numbers in respectof the relative values but comparing 40mm of woodfibre with 100mm of pir is surely not a fair comparison, and you’d never expect them to perform in a similar manner, bring up the woodfibre to the same uvale as the pir or vice versa then monitor and record what happens. Does the comparison have any real value?
  11.  
    Indeed! And one of those places is on Dartmoor so unsurprisingly it gets wetter in Winter and dries out less in Summer than the other one in Shropshire......

    One is cob, the other brick.

    That's the problem that daveking is wrestling (and me) - there's so little clean data available! And because the 'right answer' seems to depend on how much water gets into the wall in winter (location, orientation, exposure, surface treatment, construction), nobody can give out a one-size-fits-all target U value, not even in building regs.

    Interesting piece in that historic England link about trying to make WuFi prediction match up with what actually happened in real life. WuFi seems to be used lots by architects before renovations. The key parameter was the "rain adherence fraction" (how much of the rain soaked into the wall, instead of running off) and depending what number was picked from 0 to 0.1, the software predicted either doom or happiness. Unfortunately the correct value couldn't be found until a few years of site data were collected after the renovation. Without that, the architect would have to guess a "cautious" or "risky" value.

    The heritage building conservation folks and the climate conservation folks obviously have different ideas of what 'risk' means, and the householder has to balance the two!

    Also interesting that historic brick was more moisture tolerant and more insulating than the data WuFi used for modern brick, because old brick was more porous.
    • CommentAuthorArtiglio
    • CommentTimeFeb 22nd 2021
     
    Thanks for that, especially the bit about “ rain adherence fraction” probably explains the fixation some suppliers seem to have with water repellant treatments for the exterior. I eventually got fed up with suppliers suggesting masses of woodfibre ( not a great surprise seeing as they sell it) , in the end i plumped for 60mm on all but one wall which is getting 80mm ( it has a step in it , so was an easy solution). Much of the decision based on aesthetics of overly deep reveals and seeking a more comfortable home rather than ultimate u values.
    Now the roofs done and guttering up , i’ll see how things look as the weather improves and maybe trial a surface treatment once the pointing has been repaired where needed.
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