Single brick wall water penetration issues

22 Jan 2015
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United Kingdom
As as the title, I have a single brick wall outhouse. This issue is water seems to easily penetrate all the way through and cause damp. I'm looking to build another wall inside to create a cavity.
I'm not sure 100% the best way to go with regards to the damp proof membrane.

Option 1. Line walls with damp proofing membrane going about half meter into the room floor level. Lay floor membrane on top going half meter up the wall. Build wall leaving 20-40mm cavity. 2 blocks up fix membrane into the brick work.
Screed floor.

Option 2: do the above without wall membrane.

Option one I'll insulation, option 2 I'm not sure as it might pass the damp.

Thanks for any help
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You do not say what the "floor" is made out off. Take the first case, the water that penetrates the brick wall runs down between it and the vertical damp course, then spills out under the DPC but OVER the floor. This seems to be wrong to me.
I would like to see the DPC taken down into the earth lower then the prospective floor level (6"?), so the trapped water can flow(drip) away. Any DPC for the floor would have to be sealed to this vertical membrane.
Floor is concrete, so to take the water to earth I would have to either include a drainage of sorts into the lower exterior wall or dig a trench inside which is unfeasible in this case.
The floor dpc being sealed to the vertical wall membrane makes for a better idea, rather than going into the new interior wall.

I will also need to tie the walls together, I will be using right angled stainless steal brackets, fixed to the exterior and worked Into the new interior.
I may not have explained it well enough, but the floor membrane will be sat on top of the vertical membrane. Creating a bucket effect.
As for fixings is the normal method to batten the sheeting onto the wall?
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You';ll be much better off finding out why the wall is getting so wet and preventing that from happening. Outside ground level too high? Big tree nearby? Pointing fallen to bits? Insufficient eaves overhang? Missing slates/tiles? Failed flashing on an old chimney?

Much more profitable than trying to manage a damp wall...
This is a flat roofed outhouse as such. Ground level is ok, no trees etc.
It did have a concrete roof with a over hang when I bought the house. It had damp issues then.
Roof has been removed and I still need to install the guttering.
I don't think the above is helping but I also don't think it will solve the issue.
It has all been re pointed so that is sound.
If I was to treat the outside it would be a prevention and not a 100% solution.
Hence the installation of another wall to create a cavity and install of membrane at the same time.

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