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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Replacing a Damp Proof Course https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1512483658 Message started by Carlir86 on Dec 5^th, 2017, 2:20pm

Title: Replacing a Damp Proof Course
Post by Carlir86 on Dec 5^th, 2017, 2:20pm

We brought a new build ground floor flat and after flooding 3 times in 7 years the insurance company pulled up the entire DPC within the flat and lifted the block slabs to view the sub floor void were they discovered water. The Sub Soil of the development is clay and the soakaways obviously do not work.

The NHBC are scoping works and have said tanking the property is not an option as the rest of the site would still flood. Whatever solution they come up with for the site, in respect of our contained flat the DPC has been removed so can this be replaced??? or does the property need to be tanked anyway?

Title: Re: Replacing a Damp Proof Course
Post by CWatters on Dec 5^th, 2017, 6:41pm

Presumably you mean the Damp Proof Membrane (DPM) rather than the Damp Proof Course (DPC). The DPC goes between brick courses in the wall. The DPM is a sheet in/on the floor that should be lapped up the wall to at least the DPC.

Yes the DPM can and should be replaced once any investigation has been completed. Joints between sheets overlapped or better still sealed.

If soakaways don't work where does rainwater falling on the roof go? Ideally you would like rainwater/surface and water under the floor to go into the drains but not many water companies allow "mixed connections" any more.

The alternative is very large soakaways or even a soakaway mound covering a large area of land. Possibly discharge to a watercourse/ditch if one handy.

The void below the floor should also be ventilated to encourage any water under the floor to evaporate away. Look for periscope vents alow down round the outside of the block.

Good luck.

Title: Re: Replacing a Damp Proof Course
Post by CWatters on Dec 5^th, 2017, 6:44pm

PS: There is little point in just tanking. For example if the flood water gets into the drains it will come in via your WC etc. I think there are ways to prevent this as well (one way flood valves?) but I'm no expert.

It needs a carefully thought out solution rather than a piece meal approach.

Title: Re: Replacing a Damp Proof Course
Post by woodsmith on Dec 5^th, 2017, 11:02pm

You would only normally tank a basement so they should be able to replace your damp proofing to your floor without the need to tank it. Even with water under your floor though it shouldn't have produced damp in the house unless it rose above floor level.

Title: Re: Replacing a Damp Proof Course
Post by thescruff on Dec 6^th, 2017, 10:56am

Sounds like it was built on a floodplain in which case you'll never stop it.

On the other hand, if you dry the clay out the place will likely crack and fall down anyway

Title: Re: Replacing a Damp Proof Course
Post by Natedog on Dec 8^th, 2017, 7:48am

thescruff wrote on Dec 6^th, 2017, 10:56am:

Sounds like it was built on a floodplain in which case you'll never stop it.

On the other hand, if you dry the clay out the place will likely crack and fall down anyway

There's a new estate just been built other end of town from me. It's been built in a field that was always the first place the river flooded into, but they did a bit of earthworks to make a mound along the river to stop it flooding. Roughly a third of the houses have visible movement in the roof already :-/