DIY Doctor

New Floor Level Below Existing DPC When Closing up Porch

Postby nathanimate » Mon Jun 10, 2019 2:45 pm

1920's house with solid brick walls and lime mortar. We are closing up our front porch (with door an glass panels) to turn it into an internal space. We have to raise the floor (tiles on old concrete slab) by about 2-3 inches. The existing DPC on the (soon internal) double-skin wall you meet as you enter the porchway, will be above the new finished floor level, by about 4 inches. The idea is to add DPC membrane over the existing tiled floor, then add 5cm screed and then tile over. As long as we keep this below the existing DPC, I don't think there will be a problem.The issues we are facing are the following:

- We can't lime plaster or dryline all the way down to the floor level, as this is below the DPC and will bridge the DPC.
- Where would the new DPC membrane finish? At the existing DPC, 4 inches above the new floor? Higher or lower than that?
- There is suspended timber floor on the other side of the wall, so the bricks could breathe from that side. How do I make sure they can still breathe from the front as well, with the new DPC added?
- Should I cover the gap between the new floor and the old DPC with a skirting board? Would that rot? Would it still allow the bricks to breathe?
- We might even leave the brick wall unplastered if advisable, still, where would the new membrane end/go ?

Complicated I know, so I attach a picture! Thank you in advance for your help.
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