Yes, another question about garden retaining walls....

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Sorry if this one has been asked elsewhere, but I haven't been able to find a clear answer. I'm building a garden retaining wall across a sloping plot, about 1m high, about 7m long, and with a 2m length return back into the slope. I'm planning to use concrete blocks laid on side with expanded metal lath for extra strength and then face the block wall with a local stone wall using 140mm coursed split face. The back of the block wall will be infilled with 20mm pea gravel, and the whole thing will retain a patio onto which a concrete slab and summerhouse will be built. 2 questions:

1) Do I need to put DPM on the back of the blockwork? I'm not clear whether it's better to protect the blockwork from damp with DPM, or if by using it I'm effectively creating a dam, albeit with the usual drainage holes in the wall.

2) Is there any merit in leaving a cavity between the block wall and the decorative stone facing wall? If so, presumably I'll need to tie the 2 walls together, or should I do that anyway even if I build without a cavity?

Thanks in advance for any advice,

Mike
 
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Yes its best to keep the wall dry from the ground behind it. No cavity. The rear should be drained vie a land drain or weep holes in the wall
 
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I did something similar once for a freind, and we did include dpm.

Doesn't cost much and gives the added assurance even if nots a absolute requirement.
 
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Thanks 5steves, all ordered and underway from week after next.....
 
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Hey,

How did you get on with this?

I'm building a similar wall 1.2 meter high. Going 215mm thick solid block on flat.

I'm stuck trying to figure out if I need some pillars or piers to help support the wall?

Or is the block on flat enough.

Thanks.
 
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Hi Cian,
Still on with the project, been held up due to an endless set of very cold nights. I think we've had frost nearly every morning here all this month, so I've been holding off doing any cement-based work till it gets a bit warmer. Just poured some footings today, but I think it's going to be a couple of weeks before we start the blockwork. I'm no expert on any of this, so maybe others can comment, but 1.2m sounds to be getting quite high and might need a wider/deeper foundation, or maybe some rebar and hollow blocks. Or blocks laid flat and with their longest side running into the wall instead of along the wall. I've been told a rule of thumb is a maximum height of 4-5 times thickness for a retaining wall, but I guess it depends what's on the retained bit of land behind the wall. If it's just to get some more workable garden, it's obviously far less critical than an extension to the house for example.....
Sit tight, I'm sure a proper builder will be able to post some proper advice!
 

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