Damp Proof Membrane 4x25m
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Product Details
Damp Proof Membrane 4x25m is a large, durable plastic sheet designed to prevent moisture from passing through floors or walls, helping to protect your home from damp and mould. This membrane is typically made from tough black polyethylene and is supplied as a roll measuring 4 metres wide by 25 metres long, covering up to 100 square metres. It is commonly used under concrete floors, in basements, or behind wall finishes to create a waterproof barrier in new builds or renovation projects. The material is highly resistant to punctures and tears, making it suitable for heavy-duty DIY applications. Sometimes called DPM, it should be overlapped and sealed at the joints for maximum effectiveness.
As of August 2026, PriceNailer data confirms that the cheapest price for Damp Proof Membrane 4x25m is £49.90 from B&Q across 6 suppliers. Prices have increased by 4.0% over the last 9 months.
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Frequently Asked Questions
What area does a 4x25m damp proof membrane cover?
A 4x25m DPM covers exactly 100 square metres. This makes it suitable for medium to large domestic projects like single-storey extensions, garages, or basement areas.
How much should I overlap damp proof membrane joints?
Overlap DPM joints by at least 150mm (6 inches) and seal with appropriate tape or mastic. This ensures a continuous waterproof barrier and prevents moisture penetration at the seams.
Can I use 4x25m DPM under concrete floors?
Yes, this membrane is ideal for under concrete floors in new builds and extensions. It prevents ground moisture rising through the concrete slab and must be installed on a blinded hardcore base.
What thickness is standard for damp proof membrane?
Standard DPM is typically 0.25mm (250 microns) thick, providing excellent puncture resistance. This thickness meets Building Regulations requirements for most residential applications.
Do I need to protect DPM during concrete pouring?
Yes, cover the membrane with a thin sand blinding layer before pouring concrete. This prevents damage from reinforcement bars, boots, or concrete placement equipment during construction.