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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: flat roof help

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  1.  
    • CommentAuthormarsaday
    • CommentTimeMar 8th 2016
     
    have just bought a house and the flat roof is fully flat and actually has a fall away from the gutter and into a section which has a raised edge. So it pools here.

    I am doing a lot of work on the house and will be rewiring. So the plaster board ceiling is coming down in the kitchen, where the flat roof is.

    Currently there is some cotton wool type insulation. I would like to fit kingpan in there instead, but understand it is not quite as straightforward as that. I will need to leave a 50mm gap and provide ventilation.

    At the moment there is no ventilation and i am not sure if i can get any in there. So could i just fit the kingspan and fit a vapour barrier on the underside of the joists before i fit the plaster board ?

    I also need to fit firings to give the roof a proper fall.

    A warm roof sounds ok to do, but my flat roof area is 23sq/m, but only about 13 sq/m is actually a room (kitchen). The rest is a garage and so i don't need to insulate the whole area and i would need to do that is i made a warm roof.
    • CommentAuthortony
    • CommentTimeMar 8th 2016
     
    Take off deck do warm roof over kitchen, cold over garage all with min fall 1:40
    • CommentAuthorringi
    • CommentTimeMar 8th 2016
     
    Assuming the drainage works, you can have the warm flat roof higher then the rest of the roof.
    • CommentAuthormarsaday
    • CommentTimeMar 9th 2016
     
    Would i be able to insulate the void between the joists and just do a normal deck on top ? Would i get much condensation?

    It is going to make things so much harder for myself if i have to insulate on top of the deck and then make a new deck. I also need to put in some firings to create a fall. I am a bit lost with it.
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2016
     
    Posted By: marsadayIt is going to make things so much harder for myself if i have to insulate on top of the deck and then make a new deck. I also need to put in some firings to create a fall. I am a bit lost with it.

    You can buy insulation sheets that already have a fall built-in, which might make things simpler for you, but probably more expensive; I don't know their price.
    • CommentAuthortony
    • CommentTimeMar 9th 2016
     
    Likely they won't have enough fall.

    You are committed to taking the deck off I reckon as difficult to add firings without.
    • CommentAuthormarsaday
    • CommentTimeMar 9th 2016
     
    What about following the instructions in this link. This looks like what i want to do. Fill the joist space full of kingpin (150mm) and fit the boarding + furrings and fibre glass on top. Any good ?

    http://www.diydoctor.org.uk/project_images/building_a_flat_roof/warm-flat-roof.jpg

    Warm Flat Roof: By fully packing a warm flat roof with insulation there can be no air to condense. However this type of warm roof relies on there being absolutely no voids whatever otherwise interstitial condensation will occur and this can go unnoticed for many years.
  8.  
    That is not a Warm Roof. Some might say it was an accident (a condensation accident, that is) waiting to happen, unless the workmanship is 100% perfect. Yours might be, but what about someone who subsequently pricks holes in your VCL?

    A Warm Roof (note the capitals) has the structure below, and the insulation on top.
    • CommentAuthorgyrogear
    • CommentTimeMar 9th 2016 edited
     
    Hmm, I suspect you need a vapour control layer between the plasterbard and the insulation, and an airspace between the top of the insulation and the roof decking.

    (Otherwise, how will the latter breathe ?)


    Posted By: Nick ParsonsA Warm Roof (note the capitals) has the structure below, and the insulation on top.


    +1 for that ...

    gg
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2016
     
    Posted By: tonyLikely they won't have enough fall.

    available ex–stock in falls of 1:30, 1:40, 1:60 and 1:80.

    They all have BBA of course.

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