Every line built from the ground up
Cost Stack is the master pricing model. It builds each priced line from its component layers, materials, labour, plant, sub-let, preliminaries, provisional sums, risk and overhead, then reconciles the layers to the Bill of Quantities. Risk and margin are applied at line level, never bottom-loaded, so every rate is defensible at QS review and at variation.
- Project
- B99 Malthouse Block · 14 weeks
- Reference
- ITT KW-2026-4471
- Opened
- 5 May 2026
- Closed for review
- 13 May 2026
- Lead estimator
- Iola Rees-Brown
- Reconciliation
- Delta £0.00 to BoQ
Illustrative example: fictional project and parties.
The tender total, layer by layer
The £481,954.33 baseline total resolves into eight cost layers. Materials dominate, driven by the IDEAL cascade and the Stokvis plate-heat-exchanger skids. Overhead and profit is the last layer applied, at line level.
| Layer | What it covers | Value | Share |
|---|---|---|---|
| Materials | Boilers, stores, PHEs, pipework, valves, cable, insulation | £245,680 | 51.0% |
| Labour | In-house operatives at all-in rates | £81,940 | 17.0% |
| Plant and tools | MEWP, mobile tower, lighting, consumables | £13,720 | 2.8% |
| Sub-let | LARC asbestos, BMS Prime Cost Sum, crane, fire-alarm | £41,850 | 8.7% |
| Site preliminaries | BuiltAI prelims share on a sub-contractor basis | £35,260 | 7.3% |
| Provisional sums | Section I, client-led drawdown only | £17,500 | 3.6% |
| Risk pot | Contingency against named risks, not a flat rate | £8,050 | 1.7% |
| Overhead and profit | Recovery applied at line level | £37,954 | 7.9% |
| Fixed tender total, excl. VAT | £481,954.33 | 100% | |
Layer values are shown to the nearest pound; the priced total is the exact £481,954.33.
How the layers land across the sections
The same money reads a second way, as the eight priced BoQ sections. Section F, mechanical and public health, carries almost two thirds of the total and is material-led. Strip-out is sub-let-heavy because the licensed asbestos removal sits there. Preliminaries are labour and plant. The two views reconcile to the same £481,954.33.
| Sec | Package | Layer character | Total |
|---|---|---|---|
| A | Preliminaries | Labour and plant led | £51,526 |
| B | Surveys | Labour led | £8,298 |
| C | Strip-out | Sub-let led, LARC asbestos | £26,377 |
| D | Builders' work | Labour and materials | £29,596 |
| E | Testing and commissioning | Labour led | £27,601 |
| F | Mechanical and public health | Material led, includes BMS PC Sum | £296,990 |
| G | Electrical | Material and labour | £24,066 |
| I | Provisional sums | Client-led drawdown | £17,500 |
| Eight priced sections | £481,954.33 | ||
Section H, statutory notifications, prices to nil on this contract; the Principal Contractor discharges the F10 and construction phase plan.
Representative build-ups
Five of the 84 priced lines, each carried from direct cost through a named risk allowance and a line-level overhead uplift to the final tender line total. Rates use the March 2026 all-in labour card: engineer £58, fitter £52, electrician £56 per hour.
| Ref | Line item | Risk | OH&P | Line total |
|---|---|---|---|---|
| F1.1 | IDEAL EVO Max 2 boiler, supply and install | 4.0% | 7.5% | £28,340.18 |
| C7.1 | LARC asbestos removal, thermal residue | 5.0% | 6.0% | £11,817.83 |
| A6.3 | Mobile crane and lifting rig, lift-in | 8.0% | 7.0% | £9,579.92 |
| F12.5 | Phenolic insulation to primary pipework, 65 LM | 3.0% | 8.0% | £3,326.63 |
| G1.1 | Schneider Acti 9 distribution board and connection | 3.0% | 8.0% | £3,276.02 |
Risk and overhead sit on each line, not in a general margin at the bottom. That keeps every rate independently defensible at QS review and at variation negotiation under JCT Intermediate 2016, with no hidden loading in inflated rates.
The risk pot, allocated not smeared
The £8,050 risk pot is 1.7% of the total, allocated against six specific identified risks rather than a flat percentage on everything. Risks that transfer cleanly through a Provisional Sum are kept out of the pot to avoid double-counting, so escalation and instructed variations are handled elsewhere.
| Named risk | Allowance |
|---|---|
| Phase 4 lift-in weather window | £2,400 |
| Asbestos underfinds during strip-out | £1,800 |
| Existing-condition verification surveys | £1,500 |
| OEM lead-time slip | £1,200 |
| Commissioning re-attendance | £800 |
| BMS interface clarification | £350 |
| Risk pot, six named risks | £8,050 |
Six value-engineering options, priced in full
Each option is a costed alternative to the baseline specification, built up on the same March 2026 rate card as the tender, so every figure is a real delta and not a headline discount. Any option may be elected on its own or in combination, subject to written sign-off. Accepting all six takes the fixed tender from £481,954.33 to £425,217.47, a maximum saving of £56,736.86.
| Ref | Alternative to baseline | Saving |
|---|---|---|
| VE 1 | Thermal store consolidation, one 6,000 L for three 2,000 L | £9,122.00 |
| VE 2 | DHW PHE consolidation, one for two 700 kW, foregoing N+1 | £24,200.00 |
| VE 3 | Flue fire rating, 3-hour for 4-hour | £3,000.00 |
| VE 4 | DHW PHE supplier substitution, per PHE | £9,401.42 |
| VE 5 | Heating PHE format, bare exchanger for packaged | £6,590.00 |
| VE 6 | Cold-water booster substitution | £4,423.44 |
| Maximum saving, all six accepted | £56,736.86 | |
Shares are each option against the £56,736.86 on offer. The plate-heat-exchanger options carry most of the saving. VE 4 is quoted at the conservative single-exchanger figure, and if VE 2 is rejected and the paired exchangers are retained the VE 4 saving doubles, because two exchangers are then in scope.
Value engineering is offered, never assumed. Each option is held as a separate priced line so the baseline total is never eroded silently, and a saving is only taken when the client elects it in writing. VE 2 carries a resilience trade-off, since foregoing N+1 removes the standby duty on the domestic hot water exchangers.