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p / a ratio foundation

  • 03-06-2013 10:34AM
    #1
    Dully
    Registered Users, Registered Users 2 Posts: 21 ✭


    Somebody who can explain the p/a ratio of foundation systems and the way it is calculated and effects the u-value?
    Best on a real life project:
    It´s a 200mm concrete raft / slab on:
    Foundation area 179.5m², perimeter 57.1m, p/a ratio = 0.32
    Insulation base thickness 250mm, thermal conductivity 0.0338W/mK, u-value = 0.132 W/m²K
    Perimeter element thickness ("wrapping" the edge of the concrete raft) is between 150mm-200mm, lets call it 175mm for simplicity and 450mm high (level with underside of base element ), lambda 0.0388W/mK.
    All foundation / perimeter is in the ground, no perimeter exposed to the air.
    To me the change from 250mm base thickness to 175mm perimeter thickness is rather a decrease in thermal performance.

    Still the manufacturer claims a u-value 0f 0.10 for the above.
    Justified by the particuar p/a ratio for the above build up.

    How do they get this number?

    Thanks


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