What height above ground level must a Polythene DPC be installed?
Under UK Building Regulations (Approved Document C), a horizontal damp-proof course must be laid at least 150mm above the finished external ground level to prevent rainwater splashback from bridging above the moisture barrier.
How far should Polythene DPC roll edges overlap at joints?
When joining two ends of DPC along a wall run, the strips must overlap by a minimum of 100mm. At corners or junctions, overlaps should extend across the full width of the wall junction and be sealed with double-sided DPC jointing tape to ensure a continuous water seal.
How do you choose the right width of DPC roll for your wall?
DPC should match the width of the leaf or wall skin being built (100mm, 112.5mm, 150mm, etc.). It should extend completely across the mortar bed without protruding excessively from the brickwork face, which could cause external rendering or plastering to crack.
Can Polythene DPC be used under structural timber walls or wall plates?
Yes. Laying a strip of DPC directly beneath timber sole plates or wall plates sitting on concrete slabs/brick foundations prevents moisture in the masonry from transferring directly into the timber frame, avoiding wood rot.
Does Polythene DPC degrade over time inside a wall?
Low-density polythene DPC is inherently rot-proof, chemically resistant to mortar alkalis, and protected from solar UV degradation once enclosed within masonry. When correctly installed, it lasts the lifetime of the building structure.
