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Cavity tray single storey extension

Discussion in 'Building' started by xdrive, 2 Dec 2020.

  1. xdrive

    xdrive

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    Hi.

    Is it necessary to put a cavity tray/dpm above the window and door openings on a single storey extension with lean to roof and will be rendered Externally.

    Or is this more for double storey?

    Regards
     
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  3. ^woody^

    ^woody^

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    No need
     
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  4. xdrive

    xdrive

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    Cheers.

    How about where the roof will join the existing property? Will tray be required. The complete house Will be rendered Externally.

    Cavity_Wall_Abutment_with_Cavity_Tray.jpg
     
  5. ^woody^

    ^woody^

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    Yes a tray is definitely required above an attached roof even is the wall above is rendered. There is a relaxation for the requirement for weep holes in rendered walls, but I'd still put some in (the very small 10mm or so square ones) unless its imperative not to have them purely for design and aesthetics.

    If you don't form weep holes, then be sure to fit stop ends or turn the tray up at ends to hold any water in the tray and not let it spill over the edges and down the cavity.
     
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  6. xdrive

    xdrive

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    @^woody^ thank you.

    my next question is how do I go about fitting one?
     
  7. ^woody^

    ^woody^

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    You have to take out alternate sections of wall 3-4 bricks long by 3-4 course high, chase the inner leaf joint at a suitable level and then fit the tray. Then you do the adjacent sections and make sure you lap (and tape/seal the lap not just lap) the tray sections to form a continuous tray. You can use wide DPC - 300 or 450 width.

    You may have to pack the replaced bricks with slate like you do when fitting a steel beam.

    When you come to render, as its a lean-to, fit a stainless stop bead just above where the flashing will be, and chase the flashing into the wall, not the render.
     
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  8. xdrive

    xdrive

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    Awesome. Thank you very much mr woody.
     
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