Stepped DPC or cavity tray?

22 Dec 2015
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United Kingdom
I'm building an extension (cavity walls) and the ground level varies. The doors and FFL will be at 150mm but the ground will be approximately 200mm higher on one wall.

One suggestion I've had is to do a cavity tray instead of DPC as a tray doesn't need to be at 150+mm above the ground level. After thinking about it, I'm not too sure whether this would be better as it would give me a high DPC on the inside (outer DPC height + 150mm).

I'm wondering whether I can do the inner and outer DPC's at different heights. ie. +450mm on the outside and +150mm (FFL) on the inside. I've read that you can but also read that you can't :D
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