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Building up off a retaining wall

Postby Ashleyhopkin » Sat Jul 24, 2021 3:21 pm

Good afternoon all,

I’m after some advice if possible, we have built a retaining wall at the back of the garden. The neighbours garden behind us has a higher garden than ours which starts roughly in line with the top of the wall.

My question is could we use this wall to build up off for a twin skin garden room in block work? Could we add dpm to the existing wall now or if not how would we stop damp coming though? The builder has put weep holes in could these be blocked? Isit possible and if so what would we have to do?

Thanks in advance.
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Ashleyhopkin
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Postby stoneyboy » Mon Jul 26, 2021 9:56 pm

Hi ashleyhopkins
The fact that the retaining wall is holding up a 1m high soil level means that it probably be incorporated in your proposal. Raise the height of the wall by 150mm, lay a DPC on this lapped onto a vertical DPM down the wall. You could run a perforated pipe along the base of the wall to remove any seeping.
Regards S
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Postby Ashleyhopkin » Wed Jul 28, 2021 4:02 pm

Thanks stoney, the original builder said the dpm was going to be trayed across the block work? Would he have to do this at the 1m +150mm level of the external retaining wall and bring it down to 150mm to the single skin? Would you put that drainage in the cavity to exit either side of the build?

Cheers,
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Postby stoneyboy » Wed Jul 28, 2021 9:05 pm

Hi ashleyhopkin
Your builder should be able to instal a suitable arrangement for external DPC + vertical DPM against retaining wall + DPC for internal wall + DPM for floor.
Generally the vertical DPM should be lapped onto the outer DPC and down to the inner DPC, the floor DPM also lapped here. If you can drain both ways effectively that would be ideal.
Regards S
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