Waterproofing
Cavity Drain / Drainboard Calculator
Calculates area of cavity drain membrane for internal waterproofing
Updated June 26, 2026 · Live
What this tool does
Calculates area of cavity drain membrane for internal waterproofing.
Formula Used
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How the cavity drain membrane calculator works
Calculates area of cavity drain membrane for internal waterproofing. The calculator takes your dimensions and supplier rates, applies a standard Canadian trade formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.
Typical Canadian waterproofing wastage
Membranes and slurries waste 5–10% on laps and cutouts. Penetrations, internal corners, and floor drains typically increase offcut wastage. Our defaults reflect common Canadian trade allowances, and can be adjusted upwards for non-standard geometry or downwards where experience supports a lower figure.
What this tool does not do
It does not replace a professional quote, factor regional pricing, assess structural adequacy, or confirm National Building Code (NBC) compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building inspector.
On-site considerations for cavity drain membrane
Below-ground waterproofing to NBC 9.13 must be designed — Type A (barrier), Type B (structurally integral), or Type C (drained cavity), or a combination. Wrong system choice is the most common retrofit failure.
the National Building Code (NBC) and compliance
Habitable basements need full NBC 9.13 Grade 3 performance. the National Building Code covers site preparation and resistance to contaminants and moisture. When in doubt, a pre-application enquiry to the municipality can give early clarity, which tends to be less costly than retrospective correction.
Before you order
Systems from a single manufacturer are typically warrantied as a unit, and mixing products can void that warranty and complicate liability if it ever leaks. Cross-checking the calculator’s output against a supplier quote helps catch differences in pricing assumptions; the exact product specification (grade, finish, batch number) and delivery timescale are worth confirming against your programme.
Adjusting the defaults
Every input in this calculator is editable. Enter your own dimensions, supplier prices, and wastage allowance — the output recalculates instantly. If the defaults feel off for your region or project type, your own numbers always override them.
Using this cavity drain membrane calculator alongside other BuildMetricLab tools
This calculator works best as part of a planning workflow. Pair the quantity with our project contingency, labour-hours, and material-cost calculators to build a complete estimate before you pick up the phone to a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.
Sources & methodology
Calculates area of cavity drain membrane for internal waterproofing. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are cavity drain membrane calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
What wastage percentage should I use?
The calculator defaults to the typical Canadian trade allowance for waterproofing. Higher allowances suit complex cuts, awkward shapes, or first-time DIY. The default reflects common trade practice; values below it may underestimate offcuts.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, the National Building Code (NBC), property-line or shared-wall, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the unit prices?
Yes — every price field is editable. Plug in your supplier's quote to get a total that matches your project.
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