Damp Proof Course Calculator
Calculate Damp Proof Course (DPC) requirements including material quantities, overlap lengths, and a basic height check against common UK guidance.
What is a Damp Proof Course?
A Damp Proof Course (DPC) is a horizontal barrier in a wall designed to prevent moisture rising through the structure by capillary action (rising damp). DPCs are typically installed at least 150mm above ground level.
Building Regulation Requirements
- Minimum Height: DPC must be at least 150mm above finished ground level (Building Regulations Part C)
- Lap Length: Joints in DPC should overlap by at least 150mm
- Continuity: DPC must extend the full width of the wall, projecting slightly beyond the face
- Cavity Trays: Required above openings and at abutments to direct water out of the cavity
Common DPC Materials
- Polyethylene: Flexible, durable, most common for standard walls
- Bituminous Felt: Traditional material, good flexibility
- Lead: Historic buildings, very durable but expensive
- Copper: Premium option, extremely long-lasting
- Engineered Brick: Dense engineering bricks as a DPC
Standard DPC Widths
| Wall Type | Recommended DPC Width |
|---|---|
| 100mm Block | 112mm |
| 100mm Brick | 115mm |
| 215mm Brick (double) | 230mm |
| 300mm Cavity Wall | 337mm |
| Cavity Tray | 450mm |
Installation Tips
- Lay DPC on fresh mortar bed, minimum 5mm thickness
- Ensure DPC is level and free from punctures
- Maintain minimum 150mm overlap at joints
- Do not bridge DPC with continuous mortar droppings in cavity
- Ensure vertical DPC is used in cavity where external ground level is higher
UKUK Building Regulations
References & Sources
Standards Cited
- Approved Document C — Building Regulations Approved Document C: Site preparation and resistance to contaminants and moisture
Requires DPC to be installed at minimum 150 mm above external ground level to prevent rising damp; defines moisture resistance requirements for walls - BS 8215 — Code of practice for design and installation of damp-proof courses in masonry construction
Provides detailed guidance on DPC selection, lap lengths (minimum 150 mm), installation methods, and compatibility with mortar and wall types - BS 6398 — Specification for bitumen damp-proof courses for masonry
Specifies material properties, dimensions, and performance requirements for bitumen-based DPC products - BS 8102 — Code of practice for protection of below ground structures against water from the ground
Relevant to vertical DPC in cavity walls and below-ground moisture protection strategies
Formulas Used
- DPC width (single skin):
width = wall thickness + 20 mm
Source: BS 8215 — Extra 10 mm overhang each side to ensure full coverage of the mortar bed - DPC width (cavity wall):
width = (wall thickness x 2) + 25 mm
Source: BS 8215 — Allows for cavity overlap in double-skin construction - Number of laps:
laps = ceil(wall length / effective roll length) - 1
Source: BS 8215 — Effective roll length = roll length minus lap overlap (typically 150 mm). Minimum 150 mm lap at all joints - Mortar bed volume:
V = wall length x DPC width x bed depth (5 mm)
Source: BS 8215 — DPC is bedded in mortar; 5 mm bed joint depth is standard
Key Assumptions
- Minimum DPC height of 150 mm above external finished ground level — Approved Document C
- Lap length of 150 mm at all DPC joints — BS 8215
- Standard DPC roll lengths of 10 m, 20 m, and 30 m are assumed for roll quantity calculation — Manufacturer standard sizes
- Vertical DPC requirement for cavity walls estimated at 10% of wall length (for door/window reveals) — BS 8215 / building practice estimate
- Cost estimate uses approximate rates of GBP 2.50/m (narrow) to GBP 4.00/m (wide > 200 mm) — actual prices vary — Industry estimate