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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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    • CommentAuthorkilmo
    • CommentTimeJan 12th 2012
    can anyone confirm that i am doing this correctly?
    exposed permitter (m) divided by floor area m2 = unisulated floor uvalue?

    and the "exposed" is just the area on the outside walls?
    • CommentAuthorkilmo
    • CommentTimeJan 12th 2012 edited
    orange area is the solid floor, 33.6m2
    yellow line, is the perimeter 13m

    so p/a ratio is 0.38


    whats the uvalue?
    A firm on the web had a ready-reckoner which reckoned uninsulated U = 0.5 for P/A of 0.3, and U = 0.62 for P/A = 0.4. Pretty good when you consider that the blanket assumption for floors used to be 'approx. 2.0'. I gather te change in method does not make the floor any warmer, though.:(
    • CommentAuthorCWatters
    • CommentTimeJan 13th 2012


    A simplified method of calculating the U-Value of an uninsulated floor has been described in BRE Information Paper IP 3/90.

    The IP 3/90 formula is:

    U = 0.05 + 1.65(P/A) - 0.6(P/A)²


    U = U-Value of the uninsulated floor (W/m²K).

    P = Length of the exposed perimeter (m).

    A = Area of the floor (m²)
    • CommentAuthortony
    • CommentTimeJan 13th 2012
    Yea but er but majority of heat is lost from near and round the edge, it would be better to use perimeter and thickened insulation at the edges and forget the calcs!
    • CommentAuthorkilmo
    • CommentTimeJan 13th 2012
    many thanks guys

    so for my above floor with a p/a ratio of 0.38
    U = 0.05+1.65 0.38-0.6 0.38^2
    u =0.59036W/m²
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