I was somewhat surprized to notice recently that the damp proof course of the outer wall of my house extension (origonal house 1911, extensions in 1990s) is higher in some places than the DPC on the inner wall.
Is this a common practice?
SR
Yes.
The ground is often built up around the existing - patios and the like - and the B Regs requirement of the new DPC being min 150mm above ground level will not be achieved if matching the height of the original DPC.
The important point is to ensure they are lapped, so there is a continuity of DPC's, (and DPC to DPM) to there is not a round about route for damp to get in.
regards
RT
I disagree. Assuming there is a cavity between the inner and outer wall then there is no need to lap the DPC as there would be no way damp could cross the cavity. In fact I think it would be incorrect to bridge the cavity in this way as any water which had penetrated the outer wall would be directed towards the inner wall where the DPC is lower and is more likely to cause damp.
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