I have just started building an exterior wall and have laid an internal concrete slab. I am placing the DPM over the slab and under the insulation and a screed.
I understand that the DPC on the outer wall leaf needs to be a minimum of 150mm above ground level and this can be achieved no problem. However, all of my reference books show that the DPC on the inner wall leaf should be at the same level as the outer leaf, but the assumption seems to be that the internal floor level is considerably higher than the exterior ground level.
In my case the inner floor is about 25mm above the outer level. This means that the DPM would have to rise about 125mm vertically above the top of the screed to lap over the inner wall leaf at the same level as the DPC. As I cannot plaster over the DPM, then the skirting board will have to be very high to meet a surface to bond to. This is unacceptable.
My questions are: Does the DPC on the inner leaf HAVE to be at the same level as the one on the outer leaf or can it be lower? Can the DPM lap on top of the wall bricks to create a DPC or should I use a seperate DPC and bond the DPM to it? If the latter, what should I use to bond the two together.
I hope this makes sense. Any help would be most appreciated. Thanks.
Provided there is sufficient cavity depth (ie you haven't filled it to the height of the outer DPC) the DPC in the inner cavity can be lower. Fit the inner DPC onto the inner brickwork (don't forget to fill the frogs flush) and lap the DPM onto the DPC. No sealing is needed between the two.
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