The formula
For each line item we multiply a quantity by a national unit cost, then apply a quality-grade factor. A regional labor multiplier is applied to the labor portion only; materials are priced nationally. We show the itemized result as a ±22% range.
National unit costs
| Line item | National unit cost | Source |
|---|---|---|
| Outdoor condenser unit | £3,200.00 / m² | source |
| Furnace / heating unit | £2,400.00 / m² | source |
| Evaporator coil / air handler | £1,800.00 / m² | source |
| Refrigerant lineset & connections | £900.00 / m² | source |
| Ductless mini-split (outdoor + heads) | £2,600.00 / m² | source |
| Ductwork replacement | £18.00 / m² | source |
| Installation labor | £2,000.00 / m² | source |
| Permit, disposal & startup | £900.00 / m² | source |
Regional labor multipliers
Each region's labor multiplier is its mean construction-trades wage relative to the GB mean, from ONS ASHE Table 15 (SOC 531, Construction and Building Trades; 2024 revised edition) — used as a disclosed proxy because heating-system installation (ONS SOC 5314) has no usable all-region ASHE sample, mirroring the carpenter proxy in the US dataset. Multipliers are bounded to a sane range and applied to the labor share of each line item, so materials stay nationally priced while labor tracks local wages.
Data vintage and limitations
Compiled June 2026 from public cost aggregators and government wage data. These are derived estimates, not live contractor quotes. Local prices vary with project complexity, access, and material availability; always confirm with a licensed contractor before budgeting.
Tax and data notes
- VAT
- Roofing work on an existing home is standard-rated at 20% VAT across the whole UK — the same in every region. Published trade cost-guide figures are usually quoted before VAT, so we add it as a separate line and the headline estimate is VAT-inclusive — the price you actually pay. (US estimates carry no VAT; sales tax there varies by state and is excluded.)
- How firm these costs are
- The national £/m² unit costs are assembled from UK cost aggregators (Checkatrade, HomeOwners Alliance, priceyourjob) by surface, not taken from a single independent whole-roof figure, and the calculator is calibrated so the default estimate matches a cited national average. Individual line prices are therefore provisional; treat the figures as a guide and confirm with a licensed contractor before budgeting.