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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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    • CommentAuthorGBP-Keith
    • CommentTimeJan 20th 2008
    Based on what has been said so far maybe first principle advice of this article should be "Fully investigate options for external insulation first. Only when this option is ruled out should one turn to internal insulation as an option."
    • CommentAuthorjon
    • CommentTimeJan 21st 2008 edited
    >Is this actually proven Jon?<<

    There's evidence that it does Keith. For instance, damp environments accelerate the deterioration of wall ties (particularly older types common before 1990) and increase the probability of rot: The rate of deterioration found in older types of cavity wall building may be one of the reasons for moving over to stainless from galvanised. In older cavity buildings, it may also create a damp point around the timbers that sit on the inner leaf (another vulnerable detail that building regulations have changed in the last 30 years or so). Just read Tony's note: Yes, spalling is another decay mechanism that would be accelerated by internal insulation. Also, of top of head.. in some buildings where a vapour barrier has been installed, by internally insulating, one might be putting the frame into a condition where this barrier becomes on the 'cold side' and thus helping condensation to form at the interface (which again might impact on the vulnerable connections to external structure)

    Edit: lower temperatures do lower humidity (% by volume or mass) but this condition would cause higher relative humidity (% of maximum possible relative to temperature): So by lowering the temperature and not having driving energy to help evaporation, you're creating a condition where condensation is more likely to occur because in cooling cycles the relative humidity is at 100%: The lower absolute humidity would be a result of condensation.

    There are some building types that internal insulation wouldn't impact on at all.

    However, I couldn't state with certainty the CO2 impact of internally insulating versus increased demolition rates: I ran it through the model and got, for a sample timber building, a worst case impact of 10kg so it would probably be environmentally good to do this (if not financially good).

    If the mortgage and insurance companies realise that this is going on and the potential impact of doing it, there may be a problem, (in disposing of a building to which a detrimental refurb has been undertaken), in the future.

    I agree with your comment above: This is what I would do if there was even the remote possibility that the local planning department would allow it. For most people, there would be no chance of getting planning for external insulation: There may be some advantages in waiting until the Government sorts out its priorities regarding existing stock.
    • CommentAuthorNoyers
    • CommentTimeFeb 12th 2008
    All very interesting! Still got a (small) uninsulated stone farmhouse with 800+mm thick walls with no possibility of using external insulation and still clueless as to the "best" form of internal insulation. The green options (Hempcrete, Pavawall) are expensive, use a lot of space and don't have the performance of plastics foams.
    As an ex-biochemist/chemist interested in pesticide. pollutant and heavy metal analysis I'm struggling to find a solution that doesn't involve plastic foams.
    Somewhat off topic but why can't one use a totally impermeable inner wall insulation (e.g. foil based) and consider that the wall breathes (in and out) through its outer skin? Why does the inner skin need to be allowed to breathe at all? Is the wall really likely to deteriorate any faster because the inner skin doesn't breathe? The inner skin is nearly a meter away from the rain/wind/frost/sun. The interior surfaces never appear damp in winter or get warm in summer, even in 40+C summer weather.
    • CommentAuthorGBP-Keith
    • CommentTimeFeb 13th 2008
    I've got some sketches on my desk for this thread which I need to turn into drawings but I'm held up on the spring edition of green Building mag at the moment.
    • CommentAuthorpostwall
    • CommentTimeJan 31st 2009
    I share Noyer's problem: 800mm stone (dolerite) walls with rubble centre. External insulation not an option. Internal surfacea are roughly pointed and painted (emulsion).
    I would like to coat these with a thermally insulating plaster. The thickness will vary; less around areas like window reveals, more where I can get away with it. I'm thinking of using a perlite and lime mix (perhaps with some fibre added too). Does anyone have any experience of doing something similar? Is it likely to be effective. At least it should eliminate the draughts from the hairline cracks in the pointing. What about the emulsion paint, should I scratch it off?
    • CommentAuthorsinnerboy
    • CommentTimeApr 23rd 2009 edited
    Any body ever look for and/or find insulated joist hangers ? I have looked but not found . When dry lining continuity of insulation is important - and whilst it is possible to insulate in between joists of intermediate floors - how can you at the joist ends ? The worst place for interstitial condensation to arise

    Compromises occur such as - use pressure impregnated joists + fingers crossed ?
    Or firstly anchor a hardwood joist bearer along the wall and hang the joists off it

    Anybody else cracked this one ?
    • CommentAuthortony
    • CommentTimeApr 23rd 2009
    External insulation :bigsmile:
    • CommentAuthorsinnerboy
    • CommentTimeApr 24th 2009 edited
    So that's a no then Tony :cry:
    The problem of mice eating the insulation should be added to this.
    • CommentAuthorjfb
    • CommentTimeMay 20th 2014
    which type of insulation did they eat?!
    I gather from other threads that they eat anything oil based! But I believe they may be tucking into the Kingspan behind my plasterboard.
    • CommentAuthorYanntoe
    • CommentTimeMay 20th 2014
    There are a series of reports from SPAB where real life research seems to address several of concerns raised in the initial questions. There are a number of approaches being tested out in real time and in real life - and the results are re-assuring (and even a little surprising!)

    Here's a link;


    I too have an old rubble built house and there is no acceptable way to add External Wall insulation. So it has to be internally insulated where this is possible.

    The solution which seems to fit the bill is Woodfibre boards plus lime internal plastering (or PIR board).

    I think I'll go for the woodfibre option (but probably more like 100mm) plus lime and see how things go .....


    • CommentTimeMay 21st 2014 edited
    Posted By: NoyersIs the wall really likely to deteriorate any faster because the inner skin doesn't breathe?
    Most definitely yes! Much current research and WUFI simulation shows this. Water content of such a wall goes up and up year on year. Drying inward is vital.

    The totally safe way is to treat the wall as just a rain screen, copiously ventilated (to outside) on both outer and inner faces.

    Then build your insulated shell 500mm inboard of that Not everyone will like that!

    Alternatively, settle for only modest levels of internal insulation (IWI), as found safe by WUFI simulation based on local climate data - and make it very breatheable to inside. SPAB-type advice is pitched at about that level, where 'achieving Building Regs standard' is considered a triumph. We need to go much further than that.

    That you can do, if the wall's outer face is very resistant to driving rain absorbtion e.g. engineering brick. Whereas most walls - ordinary brick, ashlar stone, especially rubble stone have variously high levels of liquid absorbtion.

    It's important to distinguish between liquid water absorbtivity, and water vapour permeability. The two are largely independent. Engineering brick has low liquid water absorbtivity but good vapour permeability.

    Thorough repointing (the old deeply raked and the new 'rubbed' recessed) will help with absorbtivity.

    Then consider surface treatments which can considerably reduce absorbtivity - but note, only the highest quality, most 'scientific' ones which fully maintain vapour permeability - there are lots of gloopy retail products which clog up the pores, or form a coating and disastrously reduce vapour permeability.

    With the latter, high, almost 'eco' levels of IWI can be found safe by WUFI simulation.
    • CommentTimeMay 21st 2014 edited
    Posted By: NoyersI'm struggling to find a solution that doesn't involve plastic foams
    The worries you rightly point to, about lifetime exposure to low level cocktails of toxins, vanish completely with MHRV.

    Far from the conventional 'I wouldn't want to live in an airtight box', everyone who's lived with MHRV reports a wonderful 'mountain fresh' indoor environment because all the headachey sleepy toxins we think are 'normal', are swept away - radon too.

    That being the case, feel free to use plastic insulants - no more beneficial, eco-friendly use of petrochemicals could be imagined.
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