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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthordelprado
    • CommentTimeApr 19th 2017
    Providing there are no thermal bridges that lead to mould, is it really all that bad? Everyone talks about indoor air quality, but heating dries the air out. And dry air is also bad.

    No one complains when they are on holiday in the Philippines that the air is humid.

    Is it actually a problem? If so, what is the problem with it?
    • CommentAuthorlineweight
    • CommentTimeApr 19th 2017
    As I understand it, the risks associated with it decrease the more confident you are that you don't have any thermal bridges, as you suggest. In practice - whether they are unavoidable ones in refurb scenarios, or ones that exist thanks to bad design or workmanship - they can still be there even in supposedly well insulated buildings.

    But there is a level, I think, at which point it becomes about comfort. You'll certainly find me complaining about the humidity in hot countries. Of course, they tend to be hotter than most people would choose to have their homes.
    There are problems being too moist. Should really aim for the Goldilocks area not too dry and not too moist.
    • CommentAuthorEd Davies
    • CommentTimeApr 19th 2017
    But the red pokey things from the right are drawn on the assumption of a typical house with cold bits round the outside. The question is, if there weren't cold bits where would they end and why.

    E.g., I think the fungi, at least, need actual liquid water which will only appear below about 95% RH or so (depending on the materials) if those materials are cooler than the air.
    • CommentTimeApr 19th 2017
    Gd point - apart from this diagram I've heard lately that 80% RH is OK, comfortable.
    • CommentTimeApr 20th 2017
    Posted By: Ed DaviesBut the red pokey things from the right are drawn on the assumption of a typical house with cold bits round the outside.

    Are they? Do you have a reference that states that, Ed? I'm just asking as it seems equally likely they could be based on the actual RH reading for the effect being described.

    Fungus growth can occur at much lower humidity than you suggest according to e.g.:
    • CommentAuthordelprado
    • CommentTimeApr 20th 2017
    What are the actual requirements for fungi, though, ie why dont I get it in my hut in the the Phillipines which might be 100% humidity?
    • CommentAuthorGreenfish
    • CommentTimeApr 20th 2017
    Location (the weather outside) certainly makes a difference as to what is possible without air conditioning, and living comfortably (and I feel healthily) in the 60 to 70% RH range for most of the year leads me to question the accuracy of the 50 - 60 sweet spot.

    Good to hear 80% is "OK" Tom, any sources for this?

    Just had a dry couple of weeks, but in West Cornwall it is often "moist" outside. In spring and autumn when the outside temps are nearer the inside temps, this means that the RH inside is often on the moist side too. This is normal for Cornwall (few houses here have air-con). After getting anxious about the general RH not being in the sweet spot all the time I now accept it as the seasonal climate.

    From past experience in an old house mould can be an issue on cold spots without air movement - just being cold is not enough, lack of air movement seems to be a key thing too. Maybe your hut is drafty delprado? No mould issues in new house, MVHR keeps air moving and we have no cold spots. :)
    • CommentTimeApr 20th 2017 edited
    Posted By: GreenfishJust had a dry couple of weeks, but in West Cornwall it is often "moist" outside
    Been strange hasn't it. High RH though and mean temperatures close to dew point temperatures.
      Helston Weather.jpg
    • CommentAuthorEd Davies
    • CommentTimeApr 20th 2017 edited
    Posted By: djhAre they? Do you have a reference that states that, Ed?
    Sorry, should have phrased it better. Maybe:

    For all we know the red pokey things from the right are drawn on the assumption of a typical house with cold bits round the outside.

    I.e., just because people talking about typical houses say there's a problem at a particular RH doesn't mean there's necessarily a problem in a house which is free of cold bridges or, at least, free of cold bridges involving suitable substrates for various growths.

    The fact that there doesn't seem to be a problem with high RHs in Cornwall when everything's at around the same temperature is a pointer that those red bits aren't entirely context-free.
    • CommentAuthorgravelld
    • CommentTimeApr 20th 2017
    I was wondering as to whether the visualisation has anything to do with cold surfaces necessarily and may actually be saying that bad stuff can happen "in the air". Or something.
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