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Drainage for patio raised to near threshold/DPC

  • 17-05-2023 4:01pm
    Registered Users Posts: 153 ✭✭

    We extended our house a couple of years ago, including the obligatory wide sliding door that currently opens onto a disaster zone of a garden. With the bank account finally replenished, we're now planning to get a patio laid.

    We want to raise the patio up to the level of the doors: not literally flush with the internal floor, but level with the cill that the doors sit on. The cill is 35mm below the internal floor level and the DPC in the walls on either side of the door.

    We asked three contractors to quote for the job. All three recommended installing an aco drain where the patio meets the garden, which is fine. However, when I asked about drainage at the threshold/walls to avoid damp, they all looked baffled and said it wasn't necessary since the patio would fall away from the house.

    This conflicts with what I've read on Paving Expert, on some other DIY/construction forums, and some discussions here.

    Just wanted to ask a little more about the requirement for external ground level to be at least 150mm below the DPC, and also the concept of splashback -- I can't wrap my head around rain from the ground bouncing up at the wall being worse than rain coming in sideways at the wall as it often does.

    With a patio 35mm below the DPC and slightly below the doorframe (and its inbuilt drainage holes) would it be necessary/advisable to run an aco drain across the entire length of the house, across the doorway only, or to just rely on the fall draining water away?

    Post edited by Roy Rogers on


  • Registered Users Posts: 127 ✭✭FJMC

    We would always put an Aco type drain immediately in front of the patio doors - and often carry it along the line of the extension just to maintain paving lines, etc. - although depends on area of door and area of wall.

    You get a lot of wash off large patio doors and its also good to have additional drainage as a fail safe + removing water off the patio quicker.

    You can get different types of Aco so you could only see a 10mm slot(s) if preferred.

    Ideally dpcs, etc. would be detailed to account for higher ground levels for patios, etc.