Damp Proofing & Membranes

What we supply

• DPC rollsPolymer and bitumen damp-proof course in standard wall widths.
• DPM sheetingHeavy-gauge polythene membrane under concrete floors.
• Radon barriersGas-resistant membranes for areas that need radon protection.
• Cavity trays and stop endsTo direct water out of the cavity over openings.
• Weep ventsFor drainage and ventilation at the base of cavities and over trays.
• Liquid DPM and tankingCoatings for screeds and below-ground walls.

Sizes and specifications

DPC widths	Common widths 100 to 450 mm
DPM	1200-gauge (about 300 micron) polythene is common
DPC standards	BS 6515 (polythene), BS 6398 (bitumen), BS EN 14909 (plastic and rubber DPCs), BS EN 14967 (bitumen DPCs)

Sizes and standards are typical for the UK market; exact figures depend on the manufacturer and are confirmed on your quote.

Common uses

• New walls and extensions
• Concrete floor slabs
• Radon-affected areas
• Over window and door openings

Choosing damp proofing

Is radon protection needed?

Parts of the UK need radon protection in new buildings and extensions. UKHSA radon maps show the areas; building control will tell you what applies.

DPC width

Match the DPC width to the wall leaf so it runs the full width of the masonry.

Laps and joints

DPM and DPC need generous laps and sealed joints; follow the manufacturer's guidance.

Building regulations differ across the UK. In England, building work is checked against the Approved Documents, for example Part A for structure and Part L for energy efficiency, through your council's building control team or a registered building control approver. Wales has its own Approved Documents, including its own Part L for energy efficiency, and building control is handled by the local authority or a registered approver. In Scotland most building work needs a building warrant from the local authority, assessed against the Building Standards Technical Handbooks. In Northern Ireland building work follows the Building Regulations (Northern Ireland), with guidance in the Technical Booklets, and applications go to the council's building control team.

How it arrives on site

Rolls are light enough to travel with a mixed load and are handed off at the kerb. We agree the drop point and offload method when we price your order. Read more about how delivery works.

How much do you need?

An extension with 20 m of cavity wall needs DPC in both leaves: about 2 rolls in 30 m lengths once laps are allowed for. A 20 m² floor slab needs about 23 m² of DPM including laps, which is 1 roll of 4 × 25 m sheeting.

Damp Proofing & Membranes: questions

What is the difference between DPC and DPM?

DPC is a strip built into walls to stop damp rising through the masonry. DPM is a sheet laid under a concrete floor slab. They are lapped together so there is no gap.

Do I need a radon barrier?

It depends on where you are. In radon-affected areas building control requires radon protection in new buildings and extensions.

How thick should a DPM be?

1200-gauge polythene, around 300 microns, is a common specification for floor slabs. Your design may call for something different.

Where does the DPC go?

Usually at least 150 mm above outside ground level, linked to the floor DPM.

Do you supply cavity trays?

Yes, with stop ends and weep vents for openings and abutments.