Building up off retaining wall

8 Feb 2021
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United Kingdom
Good evening 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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It depends on the foundations, and how much higher you plan to build.
They put the footings in when they built the wall and it’s for the a garden room 6x4m by 2.5m high? I’ve had another builder come up and say it might be an issue as there’s no DPC built in? But the guy who built it said he would sort it if we went ahead with the build? I just don’t know how? The floor would be level with the current ground level as I was hoping to put ago drains in? If not a 150mm raised slab and try and reduce the roof hight so we maximise the internal head height? The garden behind is in line with the top of the current wall height? He mentioned tanking the whole wall so no moisture would come through? cheers,
They put the footings in when they built the wall
Yes, but how wide and how deep, that's the question.

The there are several ways to deal with any dampness, but whoever does it needs to know what they are doing. The wall/ floor junction of this situation can be problematic and needs to be done correctly.
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Quite wide and deep by the looks I’ll send a photo on I’m not sure exactly I’ll have to ask but he was aware i wanted to build up off it.
What’s the best practise I ensure no damp comes up through into the internal skin? My only concern is that I can’t use that retaining wall to build up off and I’ll be building another 2 walls in front of that one.


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