How it works
Sketchr is a deterministic constraint model, not a chatbot. Every figure is derived from your inputs, published rates, encoded rules and stated assumptions — and every figure can show you its working.
- 01
You describe the project
Rooms and sizes, specification tiers, the site and its constraints, your savings, monthly contribution, any lender facility, your targets and what you care about most.
- 02
The engine derives the reality
Quantities → cost ranges by package → programme → planning reading (permitted-development rules) → heating cost and indicative band → embodied carbon → structural triggers.
- 03
Phases are scheduled against your money
A cash-flow scheduler holds each phase until it is fundable, modelling stage releases from your lender, interest and a reserve floor you never go below.
- 04
You change something
Only what depends on that change is recomputed — in about a millisecond — so the consequences appear as you type.
- 05
Sketchr proposes alternatives
If a constraint breaks, it searches single and paired compensating moves, re-simulates each, and ranks them by your priorities.
- 06
You test the future
Scenarios re-run the model under shocks; regret rules and procurement windows tell you what to decide now and what to leave.
What's inside the model
| Calculator | Method (prototype) | Output | Honest limit |
|---|---|---|---|
| Quantities | Parametric take-off from room areas, storeys, envelope and openings | Areas, perimeter, glazing, roof, upper floors | ±15% at concept stage |
| Cost | Package quantities × rates × region × tier × index; preliminaries, contingency, VAT treatment | P20 / P50 / P80 by package and phase | Seed rates until licensed data and calibration |
| Programme | Productivity norms per package, regional labour factor, phase dependencies | Months per phase, unconstrained duration | Concept-stage norms |
| Planning | Encoded householder permitted-development classes (GPDO Sch. 2 Pt. 1) plus site designations | PD-likely / PD-uncertain / planning required, rules cited, route and time | A reading, not advice; no approval probability |
| Energy | Steady-state fabric heat loss × degree-days ÷ system efficiency × tariff | kWh, £/yr, indicative band | Not an EPC |
| Carbon | Quantities × embodied-carbon factors (A1–A3) | kgCO₂e total and per m² | Indicative factors |
| Structure | Span rules and load-bearing removal triggers | Beam / heavy steel flags with cost items | Flags where an engineer is needed; never a calculation |
| Pathway | Monthly ledger simulation with stage-release rules, interest, reserve floor; policies compared by lookahead | Three variants: schedule, drawdowns, stress months | Lender stage tables are typical, not your lender's |
| Trade-offs | Operator library (12 moves), single and paired search, weighted ranking | Ranked alternatives with per-dimension deltas | Library grows with founder review |