Inputs
The calculator derives required DPC width from wall thickness and skins; preset widths are shown for reference only.
Note: This is an estimating tool. Verify DPC selection and detailing with current standards and manufacturer data.
Results
Enter your wall details then click Calculate.
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