A revised floor plan lands two days before tender close. The ensuite grows, a retaining wall appears, ceiling heights change and the engineer updates the slab detail. If you update BOQ quantities by changing only the obvious line items, the tender can carry gaps through concrete, framing, linings, finishes, preliminaries and programme allowances. That is where margin disappears.
For residential builders, a BOQ revision is not an admin task. It is a controlled remeasurement and pricing exercise. The aim is to ensure every affected trade package still reflects the latest documented scope, while keeping a clear record of what has changed, what remains provisional and what needs subcontractor confirmation.
When you need to update BOQ quantities
Not every drawing revision warrants a full estimate rebuild. A changed window schedule with no change to openings, framing or finishes may only require a targeted update. But where a revision affects geometry, construction methodology or trade interfaces, assume the impact extends beyond the item that first catches your eye.
Typical triggers include revised architectural plans, structural engineering changes, civil or stormwater documentation, updated BASIX or energy requirements, consultant schedules and tender clarifications. For a granny flat, single dwelling, duplex or triplex, even a small layout movement can alter wall areas, floor finishes, waterproofing, skirtings, joinery, electrical points and the sequence of work.
The right level of review depends on the change. Moving an internal wall is not just a plasterboard quantity adjustment. Check demolition if applicable, slab set-downs, framing, insulation, doors, joinery, electrical rough-in, painting and floor finish transitions. A new deck is not merely extra square metres of decking. It may need footings, excavation, concrete, balustrades, stairs, drainage treatment and an allowance for access.
Start with a revision register, not the spreadsheet
Before editing quantities, establish exactly which documents control the pricing. Save the revised plans, schedules, engineering and written clarifications in one tender folder. Record the revision number and date against each file. Then compare them with the documents used for the current BOQ.
A simple revision register should identify the document, revision, description of change, affected BOQ sections, responsible person and pricing status. This prevents the familiar problem of a revised drawing being measured while an earlier window or finishes schedule remains in the workbook.
Mark each change as one of three types: a measured scope change, a rate change, or an allowance change. This distinction matters. A larger roof area is a quantity change. A regional builder receiving updated truss supply pricing has a rate change. Unresolved rock excavation remains an allowance issue until site information supports a measured quantity and a defensible rate.
Do not bury uncertainty inside a measured item. Keep measured scope and provisional allowances separate. It makes the tender easier to interrogate, gives the client a clearer basis for comparison and stops an unknown condition from distorting the apparent cost of known work.
How to update BOQ quantities properly
Work through the BOQ in the same order the project will be built, rather than jumping between highlighted drawings. Start with preliminaries and siteworks, then structure, envelope, internal trades, external works and project-specific allowances. This sequence exposes downstream impacts early.
Re-measure the changed area from source documents
Use the latest issued drawings as the measurement source. Do not apply a percentage uplift to the old quantity unless the scope is genuinely repetitive and the revision clearly supports it. Percentage adjustments are fast, but they create tender risk when wall types, levels, openings or construction details have changed.
Measure the revised element and retain the original take-off reference. If the slab increases by 12 square metres, check whether the perimeter has also increased. The former affects concrete, reinforcement and vapour barrier. The latter may affect edge beams, formwork, termite treatment and excavation. A quantity without a traceable source is difficult to defend when a subcontractor challenges it or the job team takes over.
Follow the change across trade boundaries
The strongest BOQs are structured so a design movement can be tracked across related packages. For example, an added bedroom may affect:
- earthworks, slab, framing and roof area
- insulation, plasterboard, cornice and painting
- flooring, skirtings, doors, hardware and wardrobe joinery
- power, lighting, data, heating and cooling capacity
- windows, flyscreens, window furnishings and façade finishes
This is not list padding. These are the line items routinely missed when a change is treated as an architectural adjustment only. A revised scope should be checked through the building fabric and then through the services that connect to it.
Check units, waste factors and inclusions
A BOQ can be numerically correct and still commercially wrong. Check that each revised item is measured in the same unit used by the relevant trade: linear metres for skirtings and gutters, square metres for linings and waterproofing, cubic metres for concrete, and itemised counts for fixtures, doors and appliances.
Review waste factors where the design has changed the cutting pattern or material type. Large-format tiles, angled roofs, raked ceilings and detailed cladding may warrant different waste allowances from a standard layout. Apply these deliberately and document the basis. Do not add blanket contingency to every trade because the drawings are incomplete.
Also confirm what is included in each line item. A plasterboard rate may include supply, fix, set and sanding but exclude insulation and access scaffolding. A roofing rate may exclude craneage or complex flashings. When quantities increase, exclusions can become more material, particularly on constrained sites or regional projects where mobilisation and freight do not scale neatly with quantity.
Reprice the BOQ without creating false certainty
Once the quantities are updated, test the rates against the revised scope. Rate cards are useful for fast tender-stage estimating, especially across NSW, QLD, VIC and regional markets, but they are not a substitute for current trade input on unusual or high-value packages.
Use subcontractor pricing packs for trades where design changes alter methodology, labour loading or procurement exposure. Structural steel, glazing, joinery, roofing, electrical, hydraulic and civil works often need this check. Issue a clean scope extract showing revision details, quantities, inclusions, exclusions and return date. Sending a subcontractor an unmarked drawing set and asking for a number invites apples-to-oranges pricing.
Where quotes have not returned, maintain a clearly stated estimate rate and identify it in the tender report. The objective is not to imply certainty that does not exist. It is to give the builder a usable position, show where the exposure sits and prioritise follow-up before contract commitment.
Protect the programme while you update quantities
Quantity changes can affect time as well as cost. More retaining, excavation or structural complexity may change lead times, crew durations, inspections and sequencing. A revised BOQ should therefore be reviewed against the indicative construction programme.
Ask whether the changed work sits on the critical path, requires an earlier shop drawing or selection decision, or creates a trade clash. An added steel beam may be a modest cost item but a major programme risk if fabrication is not allowed for. Likewise, revised joinery or glazing can move procurement dates well before the physical work reaches site.
Preliminaries deserve the same attention. If the programme lengthens, check supervision, site establishment, temporary services, hire equipment, amenities, insurance-related allowances and project management inputs. These costs are often left unchanged because they are not tied to a visible square metre quantity, yet they can materially erode margin.
Make the revised BOQ easy to audit
A builder-ready workbook should not force the next person to reverse-engineer the tender. Keep the original quantity, revised quantity, variance and reason for change visible where practical. Use revision notes at trade-package level, particularly where a change has been priced using an assumption rather than final documentation.
Your final check should reconcile the dashboard total, detailed BOQ, subcontractor packs and report assumptions. If the electrical pack has 42 downlights but the BOQ carries 38, resolve it before issue. If the programme assumes a 16-week build but preliminaries cover 14 weeks, correct the mismatch. These checks are simple, but they are where a controlled estimate separates itself from a fast spreadsheet edit.
EstiFlow’s editable BOQ workbooks are designed for this exact stage: measured quantities, rate-card logic, provisional allowances and trade breakdowns sit in a format builders can adjust without losing visibility of the estimate basis.
A revised BOQ does not need to become a full re-estimate every time a plan changes. It does need a disciplined trail from drawing revision to measured scope, trade pricing, allowances and programme. If a change is significant, compare the revised workbook against a past priced job or issue it to key trades before submission. That small check is usually cheaper than carrying an avoidable gap into a signed contract.