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.
CACalifornia Building Code (Title 24)
References & Sources
Standards Cited
- IRC R406 — International Residential Code Section R406: Foundation Waterproofing and Dampproofing
Defines moisture barrier requirements for below-grade walls including dampproofing and waterproofing methods - IRC R404.1.6 — International Residential Code Section R404.1.6: Foundation Drainage
Requires foundation drainage and moisture protection for habitable below-grade spaces
Formulas Used
- Moisture barrier width (single skin):
width = wall thickness + 20 mm
Source: IRC R406 — Extra overhang each side to ensure full coverage - Moisture barrier width (cavity wall):
width = (wall thickness x 2) + 25 mm
Source: IRC R406 — Allows for cavity overlap in double-skin construction - Number of laps:
laps = ceil(wall length / effective roll length) - 1
Source: Standard construction practice — Effective roll length = roll length minus lap overlap. Minimum 6" (150 mm) lap at all joints - Mortar bed volume:
V = wall length x barrier width x bed depth (5 mm)
Source: Standard construction practice — Barrier is bedded in mortar; 5 mm bed joint depth is standard
Key Assumptions
- NA terminology: "moisture barrier" or "dampproofing" rather than DPC; applied to below-grade foundation walls — IRC R406
- Dampproofing per IRC R406.1 required for below-grade portions of foundation walls enclosing habitable spaces — IRC R406.1
- Waterproofing per IRC R406.2 required where hydrostatic pressure exists — IRC R406.2