Garage base & retaining wall

[Pitprop]

I would appreciate some advice on damp-proofing a new concrete base for a wooden garage. As the ground where the base is to be positioned slopes up towards the rear of the base, I need a retaining wall on 3 sides. Does a dpm need to be fitted as in the diagram, or have I carried it too far?

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• Pitprop
• 1 Nov 2010
• 1

Thanks in advance for any help.

 

[freddiemercurystwin]

You're on the right track, the dpm should link up with your wall tanking. Id' do it more like the following image so that the blockwork inside the retaining wall is holding the tanking layer in place. Then at dpc level next to the coping stone I'd come off with your timber garage wall instead of blockwork. at the end of the day there are several solutions and this is just one. In principle though your floor dpm (blue) needs to be sealed with your wall dpm (or tanking (in red)) and that needs to be held in place in such a way that the pressure of the damp seeping through the earth cannot force it away from the wall if you get my drift!

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• freddiemercurystwin
• 1 Nov 2010
• 2

 

[Pitprop]

That solution looks ideal, but there are a couple of details I didn't mention that complicate things. Because the garden slopes, I had in mind that the side retaining walls would step down (approx 1m to 0 from back to front) just above ground level, rather than a constant height, and the garage I have in mind is "off the peg", so needs to be full height and therefore sit inside the retaining walls. Then I think there needs to be a small gap between the retaining wall and wooden garage wall, just large enought to be able to get in and treat the wood from time to time. However, I can see that my scheme doesn't provide any way of keeping the dmp in place at the sides.

 

[theoldun]

Personally, with no disrespect to Fred, I think you are way of track.
Whilst 1000 is no great height for a retaining wall, you are building it on top of your visqueen Slightest lateral thrust from retained ground and wall will slide of poly like sh*t of shovel. Never put poly dpc or visqueen into a retaining wall. Also unless you put lot of meat into base or a good deep toe on slab, retaining wall will only be sitting on 100mm concrete slab.
If we were doing it, we would make it two jobs. Shutter your base to size. Make sure she is square, sub base her, blind, wack, lay your dpm and turn it up side of shutter. lay slab.
Decide how much maintenance space you need, dig and concrete founds for wall, rattle up wall, MOT and wack maintenance space and spread 25mm shingle.
Take advice on construction of retaining wall.
oldun

 

[freddiemercurystwin]

Oldun, I detail the tanking for retaining walls like this all the time and always use an SE's design for the wall and found. Am not aware of one ever slipping like sh*t of shovel.

 

[theoldun]

Oldun, I detail the tanking for retaining walls like this all the time and always use an SE's design for the wall and found. Am not aware of one ever slipping like sh*t of shovel.

Freddy, Have I criticised your drawing? NO
Have I said your drawing for such a situation that you show is not correct? NO.
Have I said that I would not work to your drawing? NO.
Does your drawing show retaining wall sitting on 100mm slab and no foundation? NO
Does your drawing show retaining wall being bedded on visqueen dpm forming classic slip joint? NO
Does your drawing show maintenance access? NO

OPs drawing. Have I criticised drawing? YES
Have I said that his drawing is not correct? YES
Have I said that I would not work to his drawing? YES.
Does his drawing show retaining wall sitting on 100mm slab and no foundation? YES
Does his drawing show retaining wall being bedded on visqueen dpm forming classic slip joint? YES
Does his drawing show maintenance access? YES

See the road I am going down. Visqueen slip joint and drainage tween retaining wall and garage.
Regards, oldun

 

[Static]

Just to backup what theoldun is saying, you should never put a dpc in the bottom of a retaining wall as it creates a slip plane and basically kills the retaining wall design..
Would be worth considering making the retaining wall independant to the garage, not an integrated wall.. as you then have the option to leave the ret wall as is and modify the garage at a future date without having to rebuild both. It also means you do not need to 100% waterproof the wall and can allow some water to weep through.. this also allows you option to build a stepped retaining wall..

 

[Pitprop]

Thanks to all of the above. I have a much better idea of what needs to be done now.

 

[theoldun]

If you have any problems Pitprop, come back.
oldun