Draught Proofing Calculator

How the draught proofing calculator works

Estimates draught seal strip lengths for doors and windows. The calculator takes your dimensions and supplier rates, applies a standard UK trade formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.

Typical UK insulation and energy wastage

Rigid boards cut with 5–10% wastage depending on stud centres. Mineral wool batts waste less when cut with a sharp knife and measured with a cavity gauge. Our defaults reflect common UK 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 Building Regulations compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building control officer.

On-site considerations for draught proofing

Vapour control layers must be continuous and sealed at every service penetration. A leaky VCL lets moist air into the insulation and reduces U-value by condensation.

Building Regulations and compliance

New and renovated building fabric must meet the U-value targets in Approved Document L. SAP 10.2 is the current calculation methodology for dwellings. When in doubt, a pre-application enquiry to the local authority can give early clarity, which tends to be less costly than retrospective correction.

Before you order

Mineral wool stored outside gets damp and loses performance. Bring boards and rolls inside the weathertight envelope before install. Cross-checking the calculator’s output against a supplier quote helps catch differences in pricing assumptions — ask for exact product specifications (grade, finish, batch number) and confirm delivery timescales 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 draught proofing 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.