A duplex tender can look straightforward until the two dwellings start creating twice the interfaces, shared-site constraints and assumptions that no trade has actually priced. This NSW duplex tender checklist is built for builders who need to lodge a commercially defensible price from DA-stage plans without leaving their margin exposed to documentation gaps.
The goal is not to create a longer estimate. It is to establish measured scope, separate unknowns from known work, and issue trades with pricing packs they can return cleanly. A duplex is rarely just two single dwellings side by side. Party-wall construction, services coordination, access, civil works, authority requirements and programme sequencing need to be visible in the tender from the start.
Start with a documentation gap review
Before measuring anything, review the plan set as a tender document, not simply as a drawing package. Confirm the latest architectural, structural, hydraulic, stormwater, electrical, BASIX/NatHERS, landscape and survey information. Check revisions carefully. A superseded floor plan or structural sketch can distort quantities quickly, particularly where retaining, slab design or external works have changed.
For an NSW duplex tender checklist, the first commercial decision is whether each item is measurable, assumed or excluded. Do not bury missing information inside a composite rate. If the stormwater design is incomplete, for example, allow only for what is shown and identify the unresolved design, authority and connection risk. The same principle applies to engineering certification, acoustic details, service authority upgrades and finished levels.
Create an assumptions register alongside the BOQ. It should identify the source drawing, revision date, inclusion, allowance basis and the party responsible for confirming it. This protects the tender position and gives the project team a usable handover document if the job is won.
Measure the duplex as a coordinated site, not two houses
Split the estimate into clear cost centres: preliminaries, each dwelling, common or shared work, external works, authority-related work and provisional allowances. This structure makes it easier to see whether a cost belongs to Unit 1, Unit 2 or the development as a whole.
Measure both dwelling footprints separately, even where layouts mirror each other. Small plan variations can alter wet-area finishes, glazing, cabinetry, fire separation, roof geometry and facade quantities. Use the shared elements as their own package rather than spreading them across trade rates. Typical examples include the party wall, shared driveway, common drainage runs, crossover works, retaining walls, fencing and site establishment.
The party wall deserves a dedicated review. Confirm its construction type, structural support, fire-resistance requirements, acoustic treatment, penetrations, roof junctions and sequencing. A wall that appears simple on a DA plan may require specialist details that materially change framing, masonry, fire stopping and certification costs.
Check site and civil risk before relying on a build rate
Site costs are where a duplex tender can become uncompetitive or unprofitable if they are treated as a broad allowance. Read the survey for contours, easements, sewer location, existing structures, trees, boundary discrepancies and available access. A narrow infill site with restricted laydown and no practical material storage needs a different preliminaries and logistics allowance from a level suburban block.
Review the likely extent of demolition, excavation, spoil removal, rock, shoring, dewatering, temporary works and retaining. If geotechnical information is absent, state the allowance basis and define what sits outside it. Avoid presenting an untested excavation assumption as a measured cost.
Stormwater should be checked against the civil or hydraulic documentation, council conditions and site levels. Detention systems, on-site detention tanks, pump systems, charged lines, drainage pits and legal-point connections can all affect price and programme. Where the design is incomplete, create a provisional allowance with a clear scope boundary rather than a vague contingency.
Price preliminaries against the actual programme
Preliminaries should follow an indicative construction programme, not a percentage copied from the last job. Map the sequence from demolition and earthworks through slab, frame, roof, lock-up, services rough-in, linings, finishes, external works and approvals. Then test the period required for supervision, site amenities, fencing, scaffold, temporary power, traffic control, waste removal, security and site cleaning.
A duplex often has programme efficiencies, but not everywhere. One mobilisation can serve both dwellings, and trade continuity may improve. However, shared access, staged inspections, limited storage and the party-wall sequence can slow the job. Price those constraints honestly. A lower preliminaries figure only works if the programme supports it.
Include a realistic supervision allowance based on the builder's delivery model. A project run by a working supervisor requires a different allowance from one needing a dedicated site manager, especially on constrained sites or where multiple subcontractors need daily coordination.
Issue subcontractors a pack they can price
Do not ask trades to price from a loosely marked-up architectural set and expect comparable returns. Issue subcontractor pricing packs that clearly identify scope, drawings, specification references, tender return date, inclusions, exclusions and provisional items.
The highest-risk duplex packages usually warrant early trade engagement: excavation, concrete, framing, masonry, roofing, windows, hydraulic, electrical, mechanical ventilation, waterproofing, tiling, joinery, painting, landscaping and external civil works. For each package, check that quantities, installation requirements and interfaces are aligned. The bricklayer needs clarity on lintels, articulation joints, party-wall detail and scaffold. The plumber needs fixture schedules, sewer connection assumptions, stormwater design and meter arrangements.
Compare returns on scope, not just total price. A lower number may exclude cranage, penetrations, certification, cartage, waste, flashings, temporary protection or after-hours delivery. Normalise quotations within the BOQ so the tender comparison shows like-for-like trade coverage.
Treat allowances as controlled risk
Provisional allowances are useful when used with discipline. They are not a place to hide uncertainty. Every allowance should state what it covers, why it is provisional, whether it includes labour and margin, and what event will trigger a variation from the allowance.
For a NSW duplex, common allowance areas include rock excavation, latent conditions, authority upgrades, service connections, retaining, stormwater detention, acoustic upgrades, detailed landscaping and selected finishes where schedules are incomplete. Keep these visible in the Cost Estimate Report and avoid blending them into the base construction total.
Selections require the same treatment. If sanitaryware, appliances, tapware, tiles, flooring or joinery finishes are not fully specified, nominate an allowance level and confirm whether installation, wastage, freight and associated trade labour are included. A product allowance without the installation impact is not a complete tender position.
Test compliance and approvals before lodging
The tender should be checked against the approval pathway and the conditions already known. Review the DA conditions, BASIX commitments, bushfire or flood requirements where applicable, heritage constraints, acoustic provisions, waste management requirements, developer contributions and driveway or crossover conditions.
Some items do not sit neatly in a trade package but still affect cost and programme. These can include dilapidation reports, occupation of footpath permits, council inspections, service authority applications, asset protection measures, Section 73 requirements and certification fees. Confirm whether they are included, excluded or carried as an allowance.
This is also the point to test the estimate for construction practicality. Can excavation occur before temporary protection is installed? Does the roof design allow efficient sequencing around the party wall? Are meters, NBN pathways and service trenches coordinated before landscaping closes access? Tender risk often sits in these handovers rather than the headline building work.
Run a final margin and value-engineering review
Before submission, review the estimate at trade, cost-centre and project-total level. Check measured quantities against drawings, labour productivity against site conditions, rate cards against the project's metro or regional market, and subcontractor quotes against the stated scope. Make sure builder's margin, overheads, supervision and programme-related costs are deliberate settings, not leftovers after a target price has been chosen.
If the price needs to move, value-engineer with traceable options. Consider facade simplification, rationalised structural spans, revised retaining solutions, finish alternatives or construction sequencing improvements. Do not reduce the tender by stripping allowances or assuming trades will absorb scope gaps later. That simply transfers risk into the delivery phase.
A complete tender pack should leave the builder with an editable BOQ workbook, a builder-ready Cost Estimate Report, trade comparison detail, stated allowances and an indicative programme. EstiFlow can turn DA-stage plans and supporting documents into these tender-ready outputs in under three hours, giving the team a practical basis to review scope before quotes go out.
The useful final test is simple: could your supervisor, estimator and key trades explain exactly what the tender includes without reopening every drawing? If the answer is no, upload the plans for a measured estimate or compare the BOQ against a past priced duplex before lodging the bid.