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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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    • CommentAuthorTriassic
    • CommentTimeJul 16th 2014
     
    I'm in a high risk Radon area and need full protection. Architect has suggested a passive sump in addition to a Radon membrane. Where can I find reliable information regarding Radon Protection.

    I find it odd that Radon is the second largest killer in the Uk after smoking and yet the official radon protection document has to be paid for?
  1.  
    Yep, and it's dead hard to get clear info (or else a radon sump really is *sooooo* simple that it seems too easy.

    The sump below the extension I built last year consisted of a box made of 400 sq paving slabs below a certified radon-proof dpm, with a 100mm pipe coming off it to allow for a pump in future if required. It can also be of honeycomb brick construction.

    As for a retrofit sump, 'just dig out a bucket-sized piece of soil from below the slab'. Really? Does that really work?
    •  
      CommentAuthorted
    • CommentTimeJul 16th 2014 edited
     
    Our holiday extension has full radon protection including a pair of sumps just as Nick describes. Ends are capped "for future use". The DPM is red rather than black.

    Your BCO should be able to tell you exactly what he is looking for. Can't remember ever having to buy any document, though that may just be my bad memory as this was 10 years ago.

    Radon is heavier than air so always falls to the lowest point - hence a sump. If your build is on a slope then any sump is probably a complete waste of time but the BCO may still insist you have one.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 16th 2014
     
    Posted By: tedalways falls to the lowest point
    Do gases do that, except in high concentration, where rate of supply exceeds the rate of dispersal? That is, dispersal not by dilution (bulk air movement/mixing) but by diffusion thro still air powered by partial vapour pressure? Why should radon behave differently from other gases? Is this 'heavier than air so it sinks' one of those myths?
    • CommentAuthortony
    • CommentTimeJul 16th 2014
     
    It does tend to sink so removing air from a sump will help.

    But bear in mind that it forms inside solid rock, get out of that, it can get through concrete and polythene.
    • CommentAuthorEd Davies
    • CommentTimeJul 16th 2014 edited
     
    Radon is a lot denser than common atmospheric gasses. H₂0: 18, N₂: 28, O₂: 32, Ar: 40, CO₂: 44 g/mol whereas Rn is 222 g/mol (all give or take a few isotopes).
    •  
      CommentAuthorted
    • CommentTimeJul 16th 2014
     
    Radon comes up through the ground so the issue is to keep it out of the living space. That's what the radon-grade DPM is for. I think radon is something like ten-times heavier than air so, in the absence of draughts, it will displace air from below. If you have a good DPM then I personally cannot see the use of a sump. It seems to have become accepted as a 'belt and braces' approach where, in extremis, a fan can be connected to the pipe to suck the radon out from the foundations.
  2.  
    Where it seemed 'loosest' to me is in retrofit applications, where the removal of a bucket-sized lump of soil from below a slab which may not even have a dpm in is supposed to make everything hunky dory - sometimes even without a fan. But maybe it's fine, and at very least better than nothing.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 16th 2014 edited
     
    Posted By: Ed DaviesRadon is a lot denser than common atmospheric gasses
    Posted By: tedRadon is something like ten-times heavier than air so, in the absence of draughts, it will displace air from below
    This is assuming that radon only disperses by dilution and air movement. As I said, what about PVP-driven diffusion through still air, by which any concentration of a particular gaseous compound seeks to disperse away from its centre of concentration, even if the air etc that it's 'in' is totally static, indeed might be a sealed box.

    Maybe radon has exceptionally low PVP. That - more than its density - might be the factor that minimises its dispersal. Anyway it must be quite wrong to think of radon in air as if it's 2 immiscible liquids.
    • CommentAuthorTriassic
    • CommentTimeJul 16th 2014
     
    Forgot to say, the building in question is quite small 7.3 x 4.9m, so around 36m2. It's only 2.45m from the centre of the building to the external walls.
    • CommentAuthortony
    • CommentTimeJul 17th 2014
     
    is it on a slope?
    • CommentAuthorTriassic
    • CommentTimeJul 17th 2014 edited
     
    Posted By: tonyis it on a slope?
    at the bottom of a sloping limestone hillside.

    Having looked at various sump designs on-line, the plan is to construct a 500mm square sump out of open jointed bricks and a paving slab, with 110mm pipework running horizontally to the outside of the building and finished with a domed cover.
    • CommentAuthorTriassic
    • CommentTimeJul 17th 2014 edited
     
    Do I have to use a specific type of vapour control membrane, thickness, colour etc?

    Were should the Radon VCL be located in a ground floor slab construction? The Architect has the following build up from top to bottom -

    1 - engineered timber floor covering,
    2 - 22mm thick P5 moisture resistant chipboard, joints glued,
    3 - 1000 guage polythene VCL,
    4 - 70mm Celotex FF4000,
    5 - 150mm thick concrete slab,
    6 - Universal DPM and radon control membrane,
    7 - 75mm concrete blinding,
    8 - 150mm sub-base.

    The base is 7.3 x 4.9m, so around 36m2. Stated target U value is 0.22
  3.  
    Errr.....

    You have no floor insulation?
    • CommentAuthorTriassic
    • CommentTimeJul 17th 2014
     
    Nick - Updated to include insulation.

    Rather than a simple list, the architect has done a long written description with some repetition in other parts of the document, this somewhat confuses things.
    • CommentAuthortony
    • CommentTimeJul 17th 2014
     
    Usually you would want suspended or at least honeycomb design under the floor to allow free movement of air or radon will go through the whole floor construction. There used to be guidance on this available.
    •  
      CommentAuthorted
    • CommentTimeJul 17th 2014 edited
     
    The radon barrier is in place of the normal DPM so number 6 in your list. 1200 gauge is normal I think. Either your radon survey report or your BCO should tell you what to use.
    • CommentAuthorTriassic
    • CommentTimeJul 17th 2014
     
    The radon report makes reference to a BRE report, "Radon: guidance on protective measures for new buildings (including supplementary advice for extensions, conversions and refurbishment) (2007 ed)", costing £25.
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