Having read the dpc section I’m still struggling to understand what drainage requirements will be needed, given part of our patio will be level with dpc.
We have a stepped dpc in our north-facing extension - with bifolds on 2 sides. Everywhere except the bifolds the patio will be 150mm down from the DPC. However, underneath the bifold doors – the DPC is at the level the patio needs to sit. We cannot lower it further as it would expose the blockwork. We are planning to lay porcelain tiles and will have a fall away from the property to grass.
I think I have narrowed down to three options:
a) Pave up to DPC – as if it were a level threshold, with fall going away from house.
b) Leave a ‘splash’ strip – which will still be level with DPC. Unsure on width here, maybe 150mm but will that actually make any difference?
c) Run a linear channel drain against the extension, but again I can’t get this 75mm below the dpc, it would need to be level. On this I’m unclear how to position it relative to the overhanging cill of the bifolds. Should it be under the cill to catch water flowing off it or parallel to the edge of the cill like the diagrams on the site shows for level threshold drainage? Either way there is a risk of ending up with a gap that gets filled with leaf debris just behind it, as wouldn’t be fully flush to house at some points.
Any advice on which would be preferable or other suggestions on things I’ve missed? Thanks