Timber frame building - Dwarf wall, or not?

15 Sep 2011
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United Kingdom
I'm about to construct a timber frame building 10m X 6m. It's going to go on a concrete slab of the same size. Obviously, once the cladding goes on, the building will be a tad larger than the slab. A few people have recomended laying a single course of engineered bricks on the slab, and then place the sole plate on top of this?

Is this neccessary? If so, what do i do with the DPM from the slab? Would you then need to leave ample DPM from the concrete slab to lap over the layer of bricks, or does it go under the single course of bricks, and then a strip of damp proof course on top the bricks, and then the timber frame on top of that?

Any advice would be great, thanks in advance
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What will the building be used for? Will you be insulating over the concrete slab? Is there no membrane anywhere in the slab construction at this time?
I would use 2 brick courses in any case.
Thanks Deluks for the response. The building will be a shower/toilet building on my campsite. Only being used in the summer. Haven't started it yet, but want to do it right. How does the DPM and DPC best connect?
Dpc should be min 150mm above external ground level, dpm should be lapped over wall to meet dpc.
If this will be rough and ready facilities for campers, would you be looking to do this as a wetroom type affair? If so you may not need a dpm but bricks and dpc are essential for the timber frame, as is lots of ventilation for the timber.
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Thanks. I was going to put a DPM under the slab. If i build a course of bricks on top of the slab it should be roughy 150mm above ground. Do i then fold the DPM over the top of the bricks? And then lay the DPC on top of that, and then put my sole plate on top?

I've included a diagram, sorry struggling to get my head around it, and there doesnt seem much info on this subject.
Not great. You are leaving the dpm exposed and could get damaged. What are you planning for the floor in this shower block?? Tiled or just bare concrete?

What are you doing for drainage?
I intend to tile the floor. I was going to have surface water soakaways around the perimeter of the building and a layer of pea shingle a metre wide around the edge of the building.

What do i do with the DPM? Does it go under the single course dwarf wall? So working up: Slab - DPM under the single course brick - DPC on top of brick - Sole plate???

I've bought books, hunted high and low on the internet, cant find a definative answer anywhere??
Thanks very much for the info guys, much appreciated. The slab should protrude about 3 inches up from ground level, so i'm not going to lay any dwarf wall. The slab will only be large enough for the timber frame and sheathing, and once i clad the building in horizontal shiplap, any rain, or splash back will fall onto the pea shingle below.

I think i'm going to place the timber frame on the slab with DPC inbetween and then run the DPM up the outside of the timber frame for 300mm or so. Then have my external breather membrane come down over the top of the DPM.

I'll then attached the soleplate to the slab using Tapcon type anchors. These dont appear to have a large diameter, so shouldn't damage the DPC???? Does this sound okay, or can anyone foresee any problems??

Or, is it worth using a precast 'J-Bolt' style fixing to fix sole plate to slab, and avoid puncturing the DPC??

Thanks again
Your 3" high slab will still leave the dpc less than the min 150mm from the ground level. In any case, this will make your bottom row of timber closer to the ground and thus more susceptible to decay.

Do your slab as intended, single course of brickwork around the perimeter, then build your frame. Lay the dp membrane over the concrete slab and lapped over the brickwork. You now have a 'swimming pool' approx 75mm deep. Fill this with screed over your dpm to level the concrete ready for tiling.

Don't run the dpm outside, although ultimately the need for one is questionable considering this will be a rough n ready outhouse for Sid James to spy on Babs through the knot in your woodwork.


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