Thin Warm Deck Flat Roof Build-up

Discussion in 'Building' started by howbut82, 7 Feb 2021.

  1. howbut82

    howbut82

    Joined:
    30 Aug 2020
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    Country:
    United Kingdom
    Hi All

    I like the warm deck idea but would like to limit the roof build-up to the minimum to maximise internal headroom within a single storey extension (PD rules apply).
    Rather than the conventional "120mm PIR board above plywood deck" arrangement, I am thinking of the following buildup instead:

    (External)
    1. EPDM Waterproofing
    2. 50mm PIR Board (0.022 W/mK)
    3. 19mm Plywood
    4. 150mm Rafters with 100mm PIR Board (0.022 W/mK) between
    5. Plasterboard below rafters
    (Internal)

    This buildup should achieve a U-Value of 0.16 W/m2K and saving me 70mm in height. I checked condensation risk also in SAP software (attached) and it seems to be okay and no risk.

    I just wondering if I have missed anything here, it seems just too good to me (basically warm roof within the cold roof buildup + clear void for services above plasterboard).

    Thank you

    H
     

    Attached Files:

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