A builder assumptions register is where a residential tender stops being a collection of rates and becomes a controlled commercial position. This builder assumptions register guide explains how to document what has been priced, what remains unresolved and what must be confirmed before a job moves from DA-stage pricing into contract.
For a granny flat, single dwelling, duplex or triplex, the biggest estimating failures rarely come from a missed line of plasterboard. They come from drawing gaps, unclear site constraints, consultant information that does not align, and allowances treated as though they are firm scope. If those matters are sitting in an estimator's head, buried in an email, or spread through subcontractor quotes, they will be hard to defend later.
An assumptions register gives the project team one source of truth. It also gives the client a clear record of the basis of the price before they compare your number with another builder's tender.
What a builder assumptions register does
An assumptions register is a live schedule of decisions, qualifications, unknowns and pricing bases used to prepare an estimate. It should sit alongside the BOQ, Cost Estimate Report and subcontractor pricing packs, not replace them.
The BOQ records measured quantities and trade structure. The register explains the conditions behind those quantities and rates. For example, a BOQ may include excavation, spoil removal and retaining wall items. The register should state whether the allowance relies on a geotechnical report, assumed rock classification, nominated disposal location, access for plant and any preliminary engineering available at tender stage.
That distinction matters. A measured quantity can still be priced against incomplete information. Calling it measured does not turn an unresolved condition into a fixed cost.
Used properly, the register helps a builder do three things: issue a consistent tender, obtain comparable subcontractor returns, and identify the items that need client or consultant resolution before contract. It is tender risk management in a format people can actually use.
Build the register from the estimate, not after it
The strongest register is produced as the estimate is assembled. Do not wait until the total is complete and then attempt to recreate every judgement call behind it. At that point, qualifications tend to become vague: “allow for all works as required” or “subject to site conditions”. Those statements offer little protection and create little clarity.
Start with the documentation received. Record the drawing revision, consultant reports, planning conditions, specifications, schedules and any written client selections. Then review each trade package for information that is either missing, contradictory or not capable of firm pricing.
At DA stage, this commonly includes engineering, energy assessment requirements, detailed hydraulic design, electrical layouts, joinery documentation, external works and final finishes. The solution is not to exclude everything. It is to separate each item into one of three positions: measured and priced scope, a defined provisional allowance, or an explicit exclusion pending information.
A provisional allowance needs a basis. “Allow $X for landscaping” is weak unless it identifies the included work, the assumed area or specification, and the trigger for adjustment. A clear allowance might cover basic turf, planting, irrigation and edging to a nominated budget, while excluding retaining, feature paving and works outside the documented landscape area. The amount may change, but the commercial intent is clear.
The fields that make a register useful
A register does not need to be a complicated risk system. It does need enough detail that a project manager, estimator or director can understand the issue without reopening every plan sheet. For each item, include the following fields:
| Field | What it should establish | | --- | --- | | Reference | A unique number, trade and drawing or document reference | | Assumption or issue | The exact basis used for pricing, written in plain construction language | | Pricing treatment | Measured scope, provisional allowance, exclusion or client-supplied item | | Cost exposure | The likely direction and materiality of change if the assumption is wrong | | Action owner | The client, architect, engineer, certifier, builder or subcontractor responsible for confirmation | | Due point | When it must be resolved, such as before tender acceptance, contract or procurement | | Status | Open, confirmed, revised or closed, with the relevant revision date |
The key field is pricing treatment. Without it, a register can become a list of concerns rather than a commercial control document. Every entry needs to answer: is this included in the tender total, allowed as a variable amount, or excluded until the missing information is issued?
Write assumptions that can be tested
Avoid broad wording that creates more argument than it resolves. “Site costs allowed” tells no one what has been included. “Access assumed suitable for 10-tonne delivery vehicle and concrete pump from street frontage, with no road occupation permit or traffic control included” is specific and testable.
The same approach applies across trades. For structural steel, identify whether the price is based on preliminary engineering, architectural levels or a subcontractor concept. For glazing, identify the assumed frame system, performance level and whether final energy compliance may alter the scope. For services, state whether authority upgrades, pit relocations, sewer encasement or stormwater detention are included, excluded or carried as provisional allowances.
This precision does not make a tender look difficult. It makes it professional. A well-written register shows that the builder has understood the documents and has not hidden uncertainty inside a lump sum.
Focus on the assumptions that move margin
Not every note deserves the same prominence. A revised door hardware selection can be managed through normal procurement. A wrong assumption on excavation, access, authority works or engineering can remove the job's margin before the slab is down.
Prioritise items by cost exposure and likelihood of change. On low-rise residential work, the register should usually bring the following issues to the front:
- Site access, demolition, contamination, rock, groundwater, dewatering and spoil disposal.
- Structural design maturity, retaining, temporary works and existing-building support for additions.
- Services authority requirements, stormwater discharge conditions, fire services and utility relocations.
- Planning, certifier and council conditions that affect working hours, protection works, trees, footpaths or traffic management.
- Client selections and incomplete schedules for kitchens, bathrooms, appliances, flooring, landscaping and external works.
This is also where local knowledge matters. A rate card can provide a consistent starting point across NSW, QLD, VIC and regional areas, but local subcontractor capacity, delivery distances and site constraints can materially change the final trade price. Flag that exposure rather than pretending a metro rate transfers without adjustment.
Use the register to improve subcontractor pricing
Subcontractor pricing packs should include the relevant assumptions register entries, particularly where they affect scope boundaries. Otherwise, each trade will make its own judgement. You may receive three excavation quotes that appear comparable but carry completely different views on rock, disposal, shoring or machine access.
Ask subcontractors to confirm or qualify the stated assumptions against their price. Their response should then feed back into the register and estimate. If a plumber excludes authority fees, do not leave that exclusion in a quote email. Decide whether it is a builder exclusion, a provisional allowance or an amount to be included elsewhere in the BOQ.
This process takes discipline, but it reduces false comparison. The objective is not simply to find the lowest trade number. It is to establish what each number actually buys.
Keep it live through tender and contract
The register should be issued with the tender qualifications and reviewed at every material document revision. When drawings change, record whether the affected item is closed, revised or replaced. Do not overwrite the original assumption without preserving the decision trail.
Before contract, run a short assumptions review with the estimator, construction lead and whoever owns the client relationship. Confirm the high-value open items, the allowances that require client sign-off and the exclusions that must be carried into the contract documents. The construction programme is useful here too: an unresolved selection or engineering package may not change the tender total immediately, but it can delay procurement and create site downtime later.
Once construction starts, closed assumptions should become part of the handover pack. Open assumptions should become an action list with an owner and due date. That handover is where many tender controls fail. A site team cannot manage a qualification they have never seen.
A practical register is better than a long disclaimer
A builder assumptions register is not a legal disclaimer pasted at the end of a proposal. It is a working document that connects plans, quantities, rates, subcontractor input and programme risk. The better it is, the easier it becomes to explain the estimate, negotiate variations and protect the margin you priced.
If the documentation is still at DA stage, use the register to show what needs resolution rather than manufacturing certainty. A measured BOQ, clear provisional allowances and a disciplined assumptions register give the client a far more useful tender position than a rounded number with hidden exposure. When time is tight, upload the plans for an estimating pack that makes those assumptions visible before they become site problems.