Patio above dpc -- landscaper wants to use lead flashing...

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7 May 2009
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Hi,

Is it ok to protect a DPC by chasing in lead one course above it and laying patio up to it? Any hints on how to do it?

Landscaper has built a 120mm reinforced concrete raft for a patio to replace part of an existing patio (it's 3 ft above garden level but same level as kitchen). The raft is on top of compacted sand and aggregate. Paving slabs (not yet laid) will end slightly above the existing DPC. It was supposed to be one brick below the DPC, as the old patio was. It was always going to be tight on the DPC because the far end is fixed and we need a minimum fall. I reckon it could be at 40mm lower and still achieve the fall.

It's an old house and I've successfully resolved multiple damp issues. He's put some damp proof membrane between the raft and the wall but not everywhere and it's below the raft in places.

I'm worried water will get between the lead and the wall bricks and cause damage. They're soft bricks with lime mortar. They are already crumbling in places below the DPC. Up to the DPC we have extensive algae but almost none above the DPC. He's put the concrete raft so close to the wall (<10mm ie almost touching) we can't get in to replace or repair the bricks. With lead on top, how will water get out?

Should I ask him to dig it up and redo it lower (the falls will still work). Or to cut a trench in the raft and put in a French drain (not clear where the outlet would be)? Or to give me a guarantee (insurance backed?) against damp in the house? I quite like the guarantee solution as it's less work for him. I hate to ask him to re-do two weeks' work. Maybe there is no cause for concern?

Worrying about addressing this is making lockdown Christmas worse :(
 
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