Cavity trays - pre-formed or DIY corners?

6 Jun 2007
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United Kingdom
Hi. Hope you can help me out.

I'm trying to form a cavity tray immediately above the DPC in a new extension. I'm using Ruberoid Hyload DPC (the same as I used for the DPC) but I'm not sure what to do at the corners.

I think trying to join corners at an angle will be pretty impossible and, in reality, the tray will sit almost flat through the cavity. With the bottom of the tray flat I can join it using overlaps and jointing tape but I'm concerned this won't be acceptable to the BCO.

I see that most cavity tray manufacturers produce pre-formed cavity corners - is this the only acceptable method? (hopefully not, I'd really like to make progress during the bank holiday).

Any thoughts/advice would be appreciated.

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You would normally set the tray at dpc level externally and one course of blocks internally thus creating a slope.

This is best done with something as flexible as polythene dpm. I would not lose too much sleep over the corners so long as they are lapped and taped.

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