Question 1

What height should a DPC be above ground level?

Accepted Answer

The DPC must be at least 150 mm above finished external ground level per Approved Document C. This prevents rain splash bridging the DPC. If ground levels are raised (e.g. by paving or landscaping), the 150 mm clearance must be maintained — a common defect is paths or patios built up above DPC level, which can cause rising damp.

Question 2

What width DPC do I need?

Accepted Answer

The DPC width should be at least as wide as the wall it sits in, but should not project beyond the wall face. For a standard 100 mm blockwork inner leaf, use 100 mm DPC. For a 215 mm solid wall, use 225 mm DPC. For a full cavity wall, separate DPCs are used in each leaf. Common roll widths: 100, 112.5, 150, 225, 300, 337.5, 450 and 600 mm.

Question 3

Can I use engineering bricks instead of DPC?

Accepted Answer

Yes, two courses of Class A engineering bricks (DPC1 or DPC2 designation per BS EN 771-1) laid in 1:3 cement mortar can serve as a DPC. This was the traditional method before flexible DPCs and is still acceptable under Building Regulations. Engineering brick DPCs are very durable but more expensive and time-consuming than flexible DPC.

Question 4

What is the difference between DPC and DPM?

Accepted Answer

DPC (damp proof course) is a horizontal barrier in walls, typically at or just above ground level. DPM (damp proof membrane) is a sheet membrane under floor slabs, typically 1200-gauge (300 micron) polyethylene. The DPM must be lapped with the DPC to form a continuous barrier. Joints in DPM should be lapped at least 150 mm and taped.

Type	Material	Thickness	Notes
Polyethylene (polythene)	High-density polyethylene	~0.5 mm	Most common modern DPC, flexible, durable
Pitch polymer	Bitumen/polymer composite	~1.5–3 mm	Self-adhesive, good on uneven surfaces
Bitumen felt	Hessian-based bitumen	~2–3 mm	Traditional type, less common now
Lead-cored	Lead sheet in bitumen	~2–3 mm	Heritage buildings, cavity trays
Engineering brick	Class A engineering bricks	2 courses (150 mm)	Traditional, very durable, labour-intensive

UK DPC Specifications & Placement

DPC Material Types

Standard DPC Roll Widths

DPC Placement Rules (Approved Document C)

Related Calculators

Frequently Asked Questions

Related Calculators

Related Calculators

UK Cavity Tray Sizes

Notching and Drilling Rules

Part E Sound Reduction

UK Adhesive Types

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Width (mm)	Typical Application
100	100 mm blockwork inner leaf
112.5	Half-brick walls (102.5 mm + overhang)
150	150 mm blockwork, cavity closers
225	One-brick walls (215 mm)
300	Cavity trays, wide walls
337.5	One-and-a-half brick walls
450	Full cavity wall (both leaves + cavity)
600	Wide cavity walls, parapet walls