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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorgoodevans
    • CommentTimeJul 5th 2018 edited
     
    I have mains water passing under my beam and block flooring and will therefore have to insulate the mains pipe.

    If I use Armaflex type O insulation what thickness of insulation will I need to wrap over 32mm (26mm id) of MDPE pipe?

    Only one water board seems to have had an attempt at giving this information publicly - southen water - bottom of page 5 on this document: https://www.southernwater.co.uk/Media/Default/PDFs/WaterSupplyRegs.pdf . But these numbers seem inconsistent (issues are no idea what the asterisked numbers are - or the numbers in brackets are - and for 35mm pipe the better the insulation value the more you need !)

    There is a WRAS pipe insulation tool https://www.wras.co.uk/consumers/resources/tools/pipe_insulation_tool/# which seems comprehensive - but this tool requires the anticipated coldest temperature of the pipe in the void.

    Depending on this temperature the thickness of insulation varies dramatically - assuming a plastic pipe as above, a supply temp of 2, an insulation value of .035 W/mk and an emissivity value of 0 - if I assume a cold ambient temp of -15 deg C I need 68mm thickness of insulation - if I assume -5 deg C I need 12mm of insulation.

    Within the suspended floor void there will be significant radiated warmth from the ground, walls and floor above - but the air passing through the void could be cold - very difficult to model.

    If I was to insulate with 19mm thickness of armaflex insulation (35mm id) - routed through a 110/96 twin walled blue duct will I get any issues with my water board.
    • CommentAuthortony
    • CommentTimeJul 5th 2018
     
    Can you bury the pipe, this would effectively insulate it with soil.
    •  
      CommentAuthordjh
    • CommentTimeJul 5th 2018
     
    Posted By: goodevansIf I was to insulate with 19mm thickness of armaflex insulation (35mm id) - routed through a 110/96 twin walled blue duct will I get any issues with my water board.

    My guess is no, that seems safe. But why not ask your water board?
    • CommentAuthorowlman
    • CommentTimeJul 5th 2018
     
    djh +1
    Aren't the water authorities only responsible up to and including the meter? If the incoming mains from the meter on is yours do you need to ask can't you simply make the decision? Or did you mean something else.
    •  
      CommentAuthordjh
    • CommentTimeJul 5th 2018
     
    Your entire system is still subject to the water regulations, and the water boards enforce those regulations as far as I know.
    • CommentAuthortony
    • CommentTimeJul 5th 2018
     
    I think no insulation needed under house
    •  
      CommentAuthordjh
    • CommentTimeJul 5th 2018
     
    Posted By: tonyI think no insulation needed under house

    Apparently you haven't read the link that goodevans posted to the PDF then.
    • CommentAuthorbarney
    • CommentTimeJul 5th 2018
     
    Typically you need to insulate to prevent freezing so far as is practicable and to avoid warming of cold water services

    If you follow BS 6700 for a nominal OD of 35mm you need about 9mm of insulation thickness at 0.025W/mK

    Given the location, this typically increases to circa 15mm thick by default

    If it really will see cold draughts etc, then I would increase the thickness to 25mm

    Note insulation can't prevent freezing, only delay it and you are most at risk, close to outside wall

    Assuming that you have little or no flow in the pipe (and it's a pretty big main for a house) then minimising the length in the void and using a robust insulation thickness would make sense if you ain't ever going to see the pipe again

    In the linked PDF, the insulation thickness are stated as commercial thickness readily available, the figure in brackets are calculated thickness and the asterisk I think relates to the table note

    I'd use a good quality phenolic insulation with foil facing or even better in aluminium cladding if it's going to be a fit and forget installation

    regards

    Barney
    • CommentAuthorowlman
    • CommentTimeJul 5th 2018 edited
     
    Posted By: djhYour entire system is still subject to the water regulations, and the water boards enforce those regulations as far as I know.


    I understand that water regs apply, back siphonage etc. to avoid mains contamination but my incoming mains is uninsulated as it is in the street AFAIK, and in 34 years I've never had a problem even in the coldest winters. Provided the pipes are deep enough, I think tony's right.
    • CommentAuthorbarney
    • CommentTimeJul 5th 2018
     
    If it's down at least 750mm, then it has a reasonable insulation from air temperatures by the surrounding ground.

    We don't get frost penetration to anything like that depth

    If it's in a draughty void however- that's a different matter and Water guidelines will all point to it being insulated

    If it's under a ground bearing slab, then it will generally need insulating if it rises within 750mm of an external wall (coldest part of the floor - if it travels further than 750mm under the ground bearing slab, before rising, then it generally doesn't need insulating

    Regards

    Barney
    • CommentAuthorMike1
    • CommentTimeJul 5th 2018
     
    If you don't want to ask then for the ultimate safety margin I'd suggest going with the WRAS pipe insulation tool, assume the worst case of it being fully exposed to the external air (it may well be in a draught), and use the minimum recorded temperature for your area (https://www.metoffice.gov.uk/public/weather/climate-extremes/#?tab=climateExtremes). But why not just ask your water company or BCO?

    BTW, the pipe is supposed to be ducted or otherwise accessible to allow future repair or replacement.
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