Hidden Costs to Look for in a Building Quote: 12 Things to Check

A building quote can look detailed, professional and competitively priced—and still leave substantial costs outside the headline price.

That does not necessarily mean the builder is being dishonest. Building projects contain unknowns, selections may not be finalised and different builders include different levels of work. The problem is that most homeowners compare the large number at the bottom of each quote without first checking what sits behind it.

The lowest quote is not always the least expensive build. Before choosing a builder, you need to understand the allowances, exclusions, assumptions and items that may be charged later.

Quick answer: what hidden costs should you look for in a building quote?

The most common hidden costs in a building quote are prime cost items, provisional sums, site works, external works, utility connections, approval and consultant fees, low selection allowances, electrical upgrades, builder's margins, variations, price-adjustment clauses and owner-supplied items.

The details below explain how each cost can affect the final amount and what questions to ask before you commit.

Prime cost items

A prime cost item, commonly shown as a PC item, is generally an allowance for an item that has not been finally selected or whose exact price is not known when the contract is prepared. Common examples include:

• tapware and bathroom fittings
• tiles and flooring
• kitchen appliances
• door furniture
• sinks, basins and toilets

The allowance may look reasonable until you begin making selections. If the quote allows $30 per square metre for tiles but the products you prefer cost $65 per square metre, you will usually need to pay the difference. Depending on the contract, delivery, installation, wastage, builder's margin and GST may also affect the adjustment.

Do not simply ask whether tiles or appliances are "included". Ask:

• What exact amount has been allowed?
• Is the allowance per item, per square metre or a total amount?
• Does it include supply, delivery, installation, wastage, margin and GST?
• Can suitable products actually be purchased for the allowance?

Consumer Affairs Victoria recommends selecting fixtures and fittings and identifying them in the contract where possible, warning that unspecified prime cost and provisional sum items can increase costs and cause delays. See its guidance on managing residential building project costs.

2. Provisional sums

A provisional sum, usually shown as a PS, is an estimated allowance for work where the builder cannot determine the exact cost at the time of quoting.

Provisional sums commonly appear against:

• excavation and earthworks
• rock removal
• foundation work
• retaining walls
• drainage
• demolition
• service connections
• landscaping

If the actual cost exceeds the allowance, the owner may have to pay the difference, often with the builder's stated margin added. If the actual cost is lower, the contract should explain how the adjustment is handled.

Provisional sums are not automatically a problem. Some work is genuinely difficult to price before investigations or construction begin. The risk appears when a quote contains numerous provisional sums, unusually low allowances or vague descriptions.

Ask what information would allow each provisional sum to be converted into a fixed price. A soil test, feature survey, engineering design or clearer scope may reduce uncertainty before you sign.

South Australia's Consumer and Business Services explains that prime cost items can increase the contract price when the products selected exceed the stated allowance. It describes provisional sums as fair and reasonable best estimates for building work that cannot be accurately priced when the contract is prepared. See the SA Consumer and Business Services guidance on prime cost items and provisional sums.

3. Site costs and unexpected ground conditions

Site costs are one of the largest sources of budget movement, particularly when a quote is prepared before the site has been fully investigated.

Check whether the quote covers:

• soil classification and foundation design
• excavation and removal of excess spoil
• rock excavation
• additional piers, screw piles or deepened footings
• importation and compaction of fill
• dewatering or groundwater management
• retaining walls and batter treatment
• difficult or restricted site access
• concrete pumping, cranage or traffic control
• protection of neighbouring property

Phrases such as "standard site costs included" provide very little certainty unless "standard" is clearly defined. Ask the builder to identify the site information used to calculate the price and which conditions would trigger an additional charge.

4. Works outside the house itself

Many quotes cover the building but not everything required to make the property finished, accessible and ready to live in.

Frequently excluded external works include:

• driveways and crossovers
• paths and patios
• fencing and gates
• landscaping, turf and garden beds
• retaining walls
• decks, pergolas and outdoor structures
• clotheslines, letterboxes and television antennas
• pools and pool fencing
• sheds
• stormwater treatment outside the nominated scope

A brochure may describe a home as "turnkey", but the contract documents determine what you are actually buying. Every external item should be marked as included, excluded or supplied by the owner, with the scope clearly described.

5. Utility connections and authority charges

The quote may include services within the house but exclude the cost of connecting those services to the street, existing infrastructure or authority assets.

Check responsibility for:

• water and sewer connections
• stormwater connections or on-site detention
• electricity supply, meter installation and upgrades
• gas connections
• telecommunications and NBN infrastructure
• water tanks, pumps and treatment systems
• septic or wastewater systems where relevant
• authority application, inspection and connection fees
• trenching or unusually long service runs

Do not assume "electrical included" means the electricity connection, meter and all authority charges are included. Ask for each component to be listed separately.

6. Approvals, reports and consultant fees

A builder's quote may exclude some or all of the professional work required before construction can begin.

Depending on the project and location, these costs may include:

• planning and building approvals
• private certifier or building surveyor fees
• architectural or drafting changes
• structural, civil or hydraulic engineering
• soil testing and land surveying
• energy-efficiency assessments
• bushfire, flood, acoustic or environmental reports
• council fees, bonds and infrastructure charges
• asset-protection permits

Ask for an approvals and consultants schedule showing who arranges each item, who pays for it and whether the cost is fixed or estimated. Requirements and terminology vary between Australian states, territories and councils, so the quote should reflect the project's actual location.

7. Incomplete selections and low allowances

The words "included" and "allowance" do not mean the same thing.

A quote might include an allowance for cabinetry without stating the cabinet finish, internal layout, drawer quantity, benchtop material or hardware. Likewise, a flooring allowance may not cover preparation, trims, stairs or wastage.

Pay particular attention to:

• kitchen and bathroom cabinetry
• benchtops
• tiles and flooring
• tapware and sanitaryware
• appliances
• windows, glazing and screens
• internal and external doors
• paint systems
• wardrobes and shelving
• stairs and balustrades

Ask for brands, model numbers, quantities, dimensions and finish levels wherever possible. The more decisions made before contract signing, the fewer price surprises are likely to appear during construction.

8. Electrical, lighting, heating and cooling

Electrical allowances are often based on a basic number of points rather than the final layout a homeowner expects.

Check the quantities and specifications for:

• power points and USB outlets
• internal and external lights
• downlights and feature-light allowances
• ceiling fans
• data, television and communications points
• smoke alarms
• security systems and cameras
• air-conditioning units, zones and controls
• solar panels, batteries and electric-vehicle charging

Clarify whether decorative light fittings are supplied by the builder, allowed as a prime cost item or supplied by you. Also check who pays for installation of owner-supplied fittings.

9. Builder's margin and administration charges

The extra cost of an upgrade or variation may be more than the difference in the product price.

Depending on the contract, the builder may apply a margin or administration charge to:

• prime cost adjustments
• provisional sum adjustments
• owner-requested variations
• additional work caused by incomplete documentation
• items purchased or coordinated on the owner's behalf

Before signing, identify the percentage or fee that applies and whether GST is included. This allows you to calculate the real cost of changing a $5,000 item rather than discovering the markup later.

10. Variations after signing

A variation is a change to the agreed work after the contract has been signed. Some variations are requested by the owner; others may arise from site conditions, authority requirements, documentation gaps or necessary changes.

Variations can affect both price and completion time. Ask the builder to explain:

• how variations are requested and approved
• what supporting breakdown will be provided
• which margin or fee applies
• how credits are calculated
• whether a time extension will be claimed
• when payment is required

Do not rely on verbal agreements made on site. NSW Government guidance says large residential building contracts must include a clause requiring any agreement to vary the contract, plans or specifications to be in writing and signed by both the homeowner and contractor. See the Building Commission NSW guidance on home building contract requirements.

For a more detailed explanation, read our guide to building variations and budget blowouts.

11. Quote expiry dates and price-adjustment clauses

Quotes are usually based on current labour, material and supplier prices and may only remain valid for a limited period.

Check:

• the quote expiry date
• the assumed contract-signing date
• the assumed construction-start date
• whether the price can change if approvals or finance are delayed
• whether the contract includes price-rise, delay or legislative-change provisions
• which materials or suppliers are subject to repricing

Do not treat a quoted price as fixed until you have checked the proposed contract. The rules governing residential building contracts differ between states and territories, and significant contract clauses should be reviewed before signing.

12. Owner-supplied items

Supplying your own appliances, tiles or fixtures may appear to save money, but it can create additional costs and responsibilities.

Clarify:

• who checks measurements and suitability
• who arranges delivery and storage
• who is responsible for loss or damage
• whether installation is included
• whether the builder applies a coordination fee
• who handles defects and warranty claims
• what happens if an item arrives late and delays the build

An owner-supplied item is not necessarily an owner-installed item. Make sure the labour and coordination required to install it have been priced.

Red flags when reviewing a building quote

Look more closely when you see:

• numerous items marked TBC, TBA, by owner or excluded
• large round-number allowances without calculations
• provisional sums that appear much lower than competing quotes
• no clear inclusions and exclusions schedule
• no quantities, brands or model numbers
• a quote that is not linked to dated drawings and specifications
• conflicting information between the quote, plans, specifications and sales material
• "standard range" without access to the range
• unclear margins on variations and allowances
• pressure to sign before questions are answered

These issues do not automatically make a builder unsuitable. They indicate that the price needs further clarification before it can be compared fairly.

How to compare building quotes properly

Do not compare the headline totals alone. Create an adjusted project cost for each builder:

If you are comparing several proposals, the Builder Quote Comparison service organises the differences between up to three quotes and presents them in an adjusted-cost format.

For a fair comparison:

1. Give every builder the same drawings, engineering information and written scope.
2. Confirm each quote references the same document revisions.
3. List every inclusion, exclusion, prime cost item and provisional sum.
4. Replace unrealistic allowances with the amounts you genuinely expect to spend.
5. Add work that one builder includes and another excludes.
6. Record the margin applied to allowances and variations.
7. Identify unresolved site, approval and service-connection risks.
8. Compare specifications and quality, not just price.
9. Ask all clarification questions in writing.
10. Update the comparison when written answers are received.

NSW Government guidance also emphasises the importance of written residential building contracts and associated plans and specifications. Review the NSW Government requirements and guidance for residential building contracts.

The cheapest quote can become the most expensive build

A strong building quote should do more than present an attractive total. It should give you a clear picture of what is included, what remains uncertain and what you may need to pay separately.

Taking time to examine the detail before signing can help you:

• compare builders on a like-for-like basis
• set a more realistic total budget
• reduce avoidable variations
• make selections earlier
• ask better questions
• enter the contract with fewer assumptions

You should not need to deliver hundreds of residential projects to know what an experienced builder looks for. Your Builder Co-Pilot turns real residential building experience into practical tools that help Australian homeowners identify gaps before they become expensive surprises.

Frequently asked questions about building quotes

What are the most common hidden costs in a building quote?

The most common hidden costs are unrealistic prime cost allowances, provisional sums, site works, rock removal, retaining walls, utility connections, approvals, consultant fees, external works, electrical upgrades and builder's margins on changes. The exact risks depend on the property, documentation, contract and state or territory.

What is the difference between a prime cost item and a provisional sum?

A prime cost item generally relates to a product that has not been finally selected or priced, such as tapware, tiles or appliances. A provisional sum generally relates to work whose scope or cost cannot yet be accurately determined, such as excavation, rock removal or drainage. The proposed contract should explain the definitions and adjustment method that apply to your project.

Can the final building cost be higher than the quoted price?

It can be. The final amount may change because of prime cost and provisional sum adjustments, properly authorised variations, site conditions or other price-adjustment rights contained in the contract and permitted by applicable law. Check what is fixed, what is variable and which events can change the price before signing.

Why can two builder quotes for the same home be so different?

The builders may be pricing different specifications, quantities, site assumptions, allowance levels or exclusions, even when both quotes refer to the same plans. Converting each quote into an adjusted project cost provides a more useful comparison than looking at the headline totals alone.

How should I compare building quotes?

Start with the same drawings, engineering information and written scope. Then compare inclusions, exclusions, specifications, prime cost items, provisional sums, site assumptions, margins and owner-paid costs line by line. Ask for written clarification wherever a description or allowance is unclear.

Want help reviewing the numbers behind your quote?

Your Builder Co-Pilot is independent of building companies. We do not recommend builders or receive builder referral fees or commissions.

This article provides general educational information for Australian homeowners. It is not legal, financial, engineering, certification or building-inspection advice. Contract requirements and consumer protections differ between states and territories. Consider obtaining advice appropriate to your contract, project and location before signing.

Last reviewed: 10 August 2026