Provisional Sums in New Home Contracts: A Tasmanian Guide

When you sign a fixed-price building contract in Tasmania, not everything in it is literally fixed. Provisional sums and prime cost items are budgeted allowances for work or selections that cannot be fully specified at the time you sign — and understanding them is the key to avoiding budget surprises on your new home build.

What Is a Provisional Sum?

A provisional sum (PS) is an estimate included in your building contract for a scope of work that cannot be accurately priced when the contract is signed. The builder allows an amount based on their best assessment — but because the exact cost cannot be determined yet, the final figure is reconciled at actual cost when the work is done.

Common reasons a provisional sum is needed: the site survey and soil test have not yet been completed (so the extent of excavation is unknown), the utility connection point from the street has not been confirmed, or the civil works required to bring services to the building pad depend on as-built conditions that can only be verified during construction.

A provisional sum is not a blank cheque. Your builder must name each provisional sum, state the amount allowed, and provide you with documentation when the actual cost is known so you can see the reconciliation.

What Is a Prime Cost Item?

A prime cost (PC) item is an allowance for a specific fitting, fixture, or appliance that you — the homeowner — will select after the contract is signed. The contract includes a nominated dollar allowance; if you choose something that costs more, you pay the difference. If you choose something cheaper, you receive a credit.

Prime cost items are used for things like kitchen tapware, light fittings, appliances, floor tiles, and bathroom accessories — selections that depend on personal taste and that many homeowners want to research and choose themselves rather than being locked in at contract stage.

Why They Exist in Custom Home Contracts

Custom homes are inherently complex. Every site is different, every design is unique, and some costs genuinely cannot be confirmed until the build is underway. Standard residential building contracts used across the Australian industry — including in Tasmania — explicitly provide for both provisional sums and prime cost items. The key obligations on the builder are to:

• Clearly identify and label each provisional sum or prime cost item in the contract
• Specify the amount allowed for each
• Notify you when actual costs become known and the reconciliation is applied
• Provide documentation for any movement on the provisional or prime cost amount

Transparency is the safeguard. A provisional sum or prime cost item that is clearly named, explained, and tracked is not a risk — an unexplained one is.

Common Provisional Sums and Prime Cost Items in Tasmanian New Home Builds

Tasmania's terrain creates specific provisional sum risks that mainland builds may not face to the same degree. Basalt rock is common across the Devonport corridor and parts of the north-west — rock excavation costs vary significantly depending on volume and hardness. Coastal sites often require engineered solutions for soil stability and wastewater. Rural blocks commonly have no reticulated sewer, requiring an on-site wastewater system whose design and approval cost depends on soil permeability testing results that may not be complete at contract time.

For a builder's-eye view of what site-specific costs to anticipate, see our guide to choosing land in Tasmania.

How to Reduce Budget Uncertainty Before You Sign

The most effective way to minimise provisional sums and prime cost items is to resolve as many unknowns as possible before you sign your contract. Some practical steps:

• Commission a soil test and site survey early. A geotechnical report gives your builder the data they need to price earthworks and footing systems accurately, converting what might have been a provisional sum into a fixed-price line item.
• Get utility connection quotes before contract. TasNetworks (power), TasWater (sewer and water), and NBN Co can provide indicative connection quotes for a specific block. Getting these numbers early means your builder can quote a fixed cost rather than an allowance.
• Make your key selections during the design phase, not after signing. The more fixtures and finishes you resolve during design, the fewer prime cost allowances remain in your contract. A good builder or designer should walk you through selections before contract.
• Ask your builder to name every PS and PC item. A well-prepared contract won't have a single blanket "provisional sum — $15,000." Each item should be itemised with its own allowance and explanation.

How Davies Design & Construction Handles Provisional Sums and Prime Cost Items

At Davies Design & Construction, we work hard to minimise provisional sums and prime cost items. Where any remain, we name them, show you the allowance we have made, and reconcile them at actual cost — so you can see any movement coming before it hits an invoice.

We carry out detailed pre-contract work — site assessments, soil test reviews, design resolution — specifically to reduce the unknowns in your contract. Your price is locked for everything that has been fully specified. Where a provisional sum or prime cost item remains, it reconciles at actual cost and we show you that movement as it happens.

The building contract specifies an agreed construction period, not a calendar completion date — which is standard industry practice and honest. Factors outside any builder's control (weather events, supplier lead times, utility connection timing) affect actual completion, and promising a specific date would be misleading.

For a full overview of how pricing and contracts work at Davies, visit our Pricing Guide.

Frequently Asked Questions

Can a builder remove all provisional sums from my contract?

In practice, rarely — and a builder who claims to have done so has either resolved every unknown through extensive pre-contract work (which is valuable but time-consuming) or has absorbed the unknowns into the fixed price as contingency (which you'll pay for whether or not those risks materialise). The better approach is to minimise provisional sums through proper pre-contract work, and to ensure any that remain are clearly named, allowanced, and explained. That transparency is more valuable than a false promise of a "no provisional sums" contract.

What happens if my prime cost item selection costs more than the allowance?

If you choose a tapware range, tile, or appliance that costs more than the prime cost allowance in your contract, the difference is added as a variation. Your builder should notify you of the cost difference before you confirm the selection. If you choose something cheaper than the allowance, you receive a credit. This is why PC allowances matter: they need to be realistic, not set artificially low to make the headline contract price look smaller.

How do provisional sums affect my construction loan?

Lenders base construction loan approval on the contract price at signing. If provisional sums reconcile above allowance — or if you select PC items above allowance — the total build cost increases. You will need sufficient contingency funds to cover variations without renegotiating your loan. Most lenders and financial advisors recommend a 10% contingency buffer above your contract price. For more on construction finance, see our guide to construction loans in Tasmania.

Are provisional sums and prime cost items regulated in Tasmania?

Residential building contracts in Tasmania are governed by the Building Act 2016 (Tas) and fair trading legislation. Builders must provide a written contract for residential work over a prescribed value and must clearly disclose any provisional sums or prime cost items, including the amount allowed. Consumer, Building and Occupational Services (CBOS — cbos.tas.gov.au) is the regulatory body for building practitioners in Tasmania and handles complaints where a builder has not met their contract obligations.

How is a provisional sum different from a variation?

A provisional sum is included in the contract from the start — it's a planned allowance for known unknowns. A variation is a change to the contract scope or specification requested by you (or made necessary by unforeseen site conditions) that was not included in the original contract. Both result in adjustments to your contract price, but they arise differently and are documented differently. Your contract should define how both types of adjustments are handled and signed off.

Ready to Start Planning Your New Home?

Understanding provisional sums and prime cost items is part of being a well-prepared client. The best builder–client relationships are built on transparency about costs — including the ones that cannot be fully locked in at contract stage.

If you are considering building in northern Tasmania and want to understand exactly how your contract and budget will work, get in touch with the Davies Design & Construction team. We have been building custom homes in Tasmania since 2009 and can walk you through the contract process in plain language before you commit.