How to Estimate a Duplex or Townhouse Development
Estimating a duplex or townhouse development means pricing two things at once: the repeated cost of each individual dwelling, measured and priced as if it were its own small house, and the shared or common works — driveways, stormwater detention, shared service trenching and site-wide preliminaries — that apply once across the whole site rather than once per unit. Because most of the dwellings in a duplex or townhouse development are identical or near-identical, the estimate is built around a base unit rate that gets repeated across the development, with the shared works and preliminaries added on top as a separate site-wide layer — and any small error in that base unit rate is repeated, and therefore multiplied, every time the unit type appears again.
Key takeaways
- A duplex or townhouse estimate prices repeated unit costs across every dwelling plus shared works — driveways, stormwater, common services — that apply once across the whole site, not once per unit.
- A full Bill of Quantities across every trade is still needed for each dwelling type, because a multi-unit development is priced and contracted as one job even though the units repeat.
- Preliminaries scale with a bigger site and a longer program than a single house, covering supervision, site establishment and holding costs across all dwellings and the shared works.
- A small pricing error on one dwelling type compounds across every matching unit, so a modest shortfall on one townhouse becomes a much larger shortfall once it is multiplied across the development.
- Automated takeoff applied once and repeated automatically across a plan set of near-identical units is 60-75% faster than measuring and pricing each dwelling by hand.
A full Bill of Quantities across every trade, per unit
A Bill of Quantities for a duplex or townhouse development still needs to cover every trade for each dwelling type — site works and slab through frame, external envelope, services and fit-out — the same full scope as a single new home build, just organised so that repeating unit types are clearly identified rather than re-measured from scratch each time.
Where units are identical or mirror-imaged, the quantities for one unit type can be measured once and applied across every matching dwelling, with variations — corner units, end-of-row units, or units with an extra bedroom — measured and priced as their own distinct unit type rather than forced into the same rate as the standard unit.
- Substructure and structure — footings, slab, frame and roof, per dwelling type.
- External envelope — cladding or brickwork, roofing, windows and doors, per dwelling type.
- Services — plumbing, electrical and hydraulics, roughed in and fitted off, per dwelling.
- Internal fit-out — linings, cabinetry, tiling, flooring and painting, per dwelling type.
- Unit variations — corner, end and larger-format units measured and priced separately from the standard type.
Staging and program across a multi-dwelling site
Staging a duplex or townhouse development means deciding whether dwellings are built simultaneously, in overlapping stages, or one at a time — and that decision changes both the program and the estimate, because shared works like the common driveway or trenching often need to be substantially complete early to give every stage access, rather than left until the last unit is built.
A staged program also changes preliminaries and cash flow: sequencing units one after another lengthens the overall program and increases site supervision and holding costs, while building several units in parallel shortens the program but increases the number of trades on site — and therefore the site management — at any one time.
| Stage | Scope | Illustrative share of contract sum |
|---|---|---|
| Shared site establishment & works | Common driveway, shared stormwater, site-wide preliminaries | 12-16% |
| Units 1-5: substructure & frame | Footings, slab, frame — per dwelling, repeated 5 times | 18-22% |
| Units 1-5: external envelope | Roofing, cladding, windows, doors — per dwelling | 15-18% |
| Units 1-5: services & fit-out | Plumbing, electrical, linings, cabinetry, tiling — per dwelling | 30-34% |
| Provisional sums & PC items | Per-unit selections plus site-wide allowances | 6-10% |
| Completion & staged handover | Fixtures, final trades, staged practical completion per unit | 6-9% |
Preliminaries that scale with a bigger site
Preliminaries on a duplex or townhouse development scale with the size of the site and the length of the program, not with the number of dwellings alone — a five-unit site with a longer shared-works program can carry higher preliminaries than a larger development built quickly on a compact, single-stage program.
Because preliminaries cover the whole site for the whole program — supervision, site establishment, temporary fencing and services, insurances and holding costs — they need to be priced against the actual staging and program you have planned, not carried over unchanged from a single-house estimate.
Provisional sums and PC items across every unit
Provisional sums and PC items still apply on a duplex or townhouse development, but they need to be considered both per dwelling and at a whole-of-site level, because some allowances — a kitchen or tapware selection, for example — repeat identically across every matching unit, while others — a service connection allowance, or ground conditions for the shared driveway — apply once to the whole site.
Carrying a PC item once and assuming it covers every unit is a common way these allowances quietly under-price a multi-dwelling job — a kitchen PC item priced for one dwelling needs to be multiplied by the number of matching units, not left as a single site-wide allowance.
- Per-unit PC items — kitchen, tapware, tiles and light fittings, priced once per dwelling type and multiplied by the number of matching units.
- Site-wide provisional sums — authority service connections, ground conditions for shared works, and staging-related allowances.
Small errors, multiplied — and progress claims across a staged build
A small pricing error on one dwelling type is not a small error on the development as a whole, because it repeats every time that unit type appears — a rate that is a little light on one two-bedroom townhouse becomes a much larger shortfall the moment it is applied across five identical units, without a single extra mistake being made.
This compounding risk is why the base unit rate deserves more scrutiny on a multi-dwelling job than the same rate would on a single house, and why progress claims — usually billed per unit and per stage against the value of work actually complete — become harder to reconcile once an underlying rate error has been carried through every claim on every matching unit.
Why a 2% gap per unit is not a 2% gap overall
A 2% pricing gap on a single dwelling stays a 2% gap. The same 2% gap in a base unit rate that is repeated across five matching townhouses becomes a 2% gap multiplied five times over — and it shows up in every progress claim raised against that unit type, not just the final one.
How My Trade Hub helps estimate a duplex or townhouse development
My Trade Hub performs the automated takeoff across your full plan set, measuring each repeating dwelling type once and applying that measurement consistently across every matching unit, alongside a separate takeoff for the shared works — driveways, common services and site-wide preliminaries — so the two layers of a multi-dwelling estimate stay properly distinct.
Your own editable rates library is applied automatically across every measured quantity, which means a correction to a base unit rate is corrected everywhere that unit type appears, instead of being fixed in one place and missed in the other four — directly addressing the way small errors compound across a repeated-unit development.
The result is assembled into a structured Bill of Quantities and tender, organised by dwelling type and by shared works, ready to price provisional sums and PC items at the right level and issue as one tender document — and because the takeoff is automated rather than remeasured unit by unit, preparing a priced tender for a multi-dwelling development is 60-75% faster than doing it by hand.
Frequently asked questions
how do you estimate a duplex or townhouse development?
You estimate a duplex or townhouse development by pricing a repeated base cost per dwelling type — measured once and applied across every matching unit — plus a separate layer of shared works such as common driveways, shared stormwater and site-wide preliminaries. Automated takeoff applied once across a plan set of near-identical units is 60-75% faster than measuring and pricing each dwelling by hand.
how is pricing a duplex different from pricing a single house?
Pricing a duplex or townhouse adds a shared-works layer that a single house doesn’t have — a common driveway, shared stormwater detention, and service trenching that belongs to the site as a whole rather than to one dwelling — and it introduces repeated unit costs, where the same base rate for a dwelling type is applied across every matching unit rather than priced once.
what counts as shared or common works on a townhouse development?
Shared or common works typically include the common driveway or access way, shared stormwater detention and drainage, retaining walls serving more than one lot, shared service trenching and pits, and any easements or common-property landscaping — all priced once for the whole site rather than split across individual dwellings.
how do preliminaries work on a multi-dwelling development?
Preliminaries on a duplex or townhouse development scale with the size of the site and the length of the program rather than with the number of dwellings alone, covering site-wide supervision, establishment, insurances and holding costs for the whole build — and they need to be priced against your actual staging plan, not simply carried over from a single-house estimate.
why do small pricing errors matter more on a multi-unit development?
A small error in a base unit rate is repeated every time that dwelling type appears, so a modest per-unit shortfall is multiplied across every matching unit in the development — a rate that is a little light on one townhouse becomes a much larger shortfall once it has been applied across five or more identical units.
how do progress claims work across multiple dwellings?
Progress claims on a duplex or townhouse development are usually billed per unit and per stage, against the value of work measured as complete on each dwelling — which is why a Bill of Quantities organised by dwelling type and by shared works makes each claim straightforward to justify, and why an error in the base unit rate shows up in every claim raised against that unit type.
how do provisional sums and pc items work across multiple units?
Provisional sums and PC items on a duplex or townhouse development need to be considered both per dwelling and site-wide — a kitchen or tapware PC item repeats per matching unit and should be multiplied by the number of dwellings it applies to, while a service-connection allowance or ground-conditions provisional sum for the shared works applies once to the whole site.
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