In the construction world, from towering skyscrapers to residential homes, the foundation isn’t just in the concrete or steel—it’s also in the contracts that bind the vision to reality. These contracts are blueprints for expectations, budgets, and timelines, guiding projects to successful completion. But they’re more than just paperwork; they’re a critical tool for managing risk, detailing responsibilities, and ensuring clear communication between all parties involved.

Understanding the nuances of the different types of contracts is crucial for any construction professional, as the right contract can mean the difference between a project’s success or a spiral into dispute.

In Australia, construction disputes are commonly centred around issues of time, cost, or quality, and are often escalated due to breakdowns in communication and differing interpretations of contractual obligations. It’s evident that understanding and choosing the right contract type is vital in avoiding these disputes and ensuring project success.

As we dive deeper into the eight types of construction contracts you should have, we’ll explore how each can effectively manage different aspects of construction projects, mitigate risks, and pave the way for a successful build.

1. Cost-Plus Construction Contract

A Cost-Plus Construction Contract is an agreement where payment is based on the actual costs of construction plus an additional fee as profit. It’s like when you do a project, and you get paid back for all the materials you bought, plus a bit extra for your hard work. This type of contract is often used when the project scope isn’t entirely clear from the start, or when there’s a chance that the plan might change along the way.

When to Use It:

You’d go for a Cost-Plus Contract when the project details are not set in stone, or when you want high-quality work without cutting corners. It’s perfect for jobs where new ideas might pop up during the construction process that could change the direction or design of the project.


  • Flexibility: This contract, often supported by construction solicitors, allows changes to be made during the project.
  • Transparency: You get to see exactly where your money is going since all expenses are reported.
  • Quality: Since the contractor gets paid for all the actual costs, they’re not tempted to go cheap on materials.


  • Budget Uncertainty: You don’t know the final cost until the end.
  • Detailed Accounting: The contractor has to keep a detailed record of all expenses, which can be a lot of paperwork.
  • Potential for Higher Costs: If the contractor finds out they need more materials or if a job takes longer, the cost will go up.

2. Design and Build Contract

A Design and Build Contract, often negotiated with the help of a building contract solicitor, is a deal where one team is responsible for both designing and constructing a project. This contract is handy because you only have to talk to one group of people instead of a separate designer and builder.

When to Use It:

Use this type of contract when you want a one-stop-shop for your project. It’s ideal if you’re looking for speed in the construction process and when you want to minimise the hassle of coordinating between different teams.


  • Simplicity: One team does it all – from the initial design to the final nail, reducing the number of people you need to deal with.
  • Time-Saving: Because the same team is designing and building, the process can move faster than traditional methods.
  • Accountability: One team is accountable for the entire project, which means less finger-pointing if something goes wrong.


  • Less Control: Since the same team is doing everything, you might feel like you have less say in the individual stages of the project.
  • Potential for Higher Costs: Without separate bids for design and construction, it’s harder to compare prices.
  • Limited Flexibility: Changes mid-project can be trickier because everything’s more interconnected.

3. Guaranteed Maximum Price Contract

A Guaranteed Maximum Price Contract, often shortened to GMP, means that the contractor agrees to complete the project at a set maximum price. If the project goes over this price, the contractor covers the extra costs.

How It Works:

The GMP is determined based on the contractor’s estimate of the total project cost, including labour, materials, and their own fee. This cap protects the project owner from unexpected expenses during construction.

Financial Caps:

The “guaranteed maximum” part is the financial cap, the max amount the owner will pay. The contractor is responsible for any costs that exceed this cap, giving them an incentive to manage the project efficiently.


  • Budget Control: The owner knows the most they will have to pay, which helps with financial planning.
  • Potential Savings: If the project comes in under budget, the owner might benefit from the savings.
  • Incentive for Efficiency: Contractors have a reason to keep costs down and work efficiently to avoid paying out of pocket for overages.


  • Possible Quality Compromise: Contractors might choose lower-quality materials or methods to stay under the cap.
  • Complexity in Accounting: Keeping track of costs can become complex, especially if there are many changes during the project.
  • Risk for Contractors: Contractors take on the risk of cost overruns, which could reduce their profit or even lead to a loss.

4. Incentive Construction Contract

An Incentive Construction Contract is a type of contract where the contractor gets extra benefits, often financial, for finishing a project early or under budget, or for meeting certain performance goals. It’s designed to motivate the contractor to work efficiently and effectively.

Structure of Incentives:

The incentives are usually set as clear targets in the contract. For instance, if the contractor finishes the project two weeks early, they might get a bonus. Or if they manage to save money on the budget, they could get a percentage of those savings. These targets are agreed upon at the start and are meant to align the contractor’s goals with the project owner’s.


  • Motivation to Perform: Contractors are driven to meet or exceed project goals.
  • Cost Savings: If the project is completed under budget, both the contractor and the owner can benefit financially.
  • Timely Completion: Incentives for early completion can lead to a quicker project turnaround.


  • Complex Negotiations: Figuring out the incentives can require a lot of back-and-forth discussions before starting.
  • Potential for Cutting Corners: Contractors might prioritise speed over quality to meet incentive targets.
  • Risk of Disputes: If the goals aren’t crystal clear, disagreements can arise about whether the incentives should be paid out.

5. Integrated Project Delivery Contract

An Integrated Project Delivery (IPD) Contract is where all the key players form one big team with a shared goal: to finish the project efficiently and effectively. They share the risks and the rewards, with the idea being that teamwork leads to better results.

Description of the Collaborative Contract Model:

The IPD contract, often crafted with QBCC lawyers’ expertise, establishes a partnership where the owner, designer, and builder all work closely from the project’s start to its finish. They make decisions together and share information openly, which helps to avoid surprises and delays. The contract typically includes a commitment to use efficient workflows and to make decisions that are best for the project as a whole, not just one party.


  • Enhanced Collaboration: Everyone works together, leading to better communication and problem-solving.
  • Shared Risk and Reward: If the project goes well, everyone benefits; if there are overruns, the pain is shared, too.
  • Efficiency: With shared goals, the project can often be completed faster and with less waste.


  • Complexity: Setting up an IPD contract can be complex because it has to define the roles and rewards for many different parties.
  • New Processes: Teams may need to learn new ways of working together, which can take time.
  • Reliance on Team Dynamics: The success of the project depends on the ability of the team to work together well, which isn’t always a sure thing.

6. Lump-Sum Contract

A Lump-Sum Contract is where the contractor agrees to complete the project for a fixed total price, no matter what happens during the building process.

Premise of a Fixed Total Price:

The contractor calculates the total cost of the project, including materials, labour, and their profit, and then gives you one total price. This price is set in stone, and you won’t pay more if the costs go up during the project.

Limitations and Project Suitability:

This contract is best for projects with a well-defined scope where not much is expected to change. It’s not so great for projects that are more open-ended or likely to change a lot, because there’s no wiggle room in the budget.


  • Budget Certainty: You know exactly how much the project will cost right from the start.
  • Simplicity: The contract is straightforward, with no need to track costs as the project goes along.
  • Incentive for Efficiency: Contractors have a reason to be efficient because any cost savings go straight to their profit.


  • Risk for Contractors: If the costs are higher than expected, the contractor has to pay the difference.
  • Potential for Disputes: If changes are needed, negotiating who covers the extra costs can cause arguments.
  • Less Flexibility: Once the price is set, it can be costly to make changes or add new features.

7. Time and Materials Contract

A Time and Materials Contract is where the owner pays for the actual time spent on the job and the materials used.

Pay Structure Based on Time and Material Costs

The contractor tracks the hours their team works and the actual cost of materials, then adds a markup for profit. This total becomes the bill for the project owner.

Transparency and Flexibility Considerations

This contract is transparent because the owner can see exactly where their money is going. It’s also flexible, allowing for changes in the project without renegotiating the entire contract.


  • Adaptability: If the project needs to change direction, this contract can handle it.
  • Clarity: Owners can see the cost of labour and materials, which can build trust.
  • Fairness: Contractors get paid for all the work they do, even if the project takes longer than expected.


  • Uncertain Costs: The final price isn’t known at the start, which can be nerve-wracking for owners.
  • Requires Oversight: Owners need to keep an eye on expenses to make sure they stay reasonable.
  • Potential for Higher Costs: If the project drags on, or if materials are expensive, the price can climb.

8. Unit Price Contract

In a Unit Price Contract, typically overseen by commercial contract lawyers, charges are based on the number of units completed, such as the square footage paved or the number of windows installed.

Pricing Based on Per Unit Costs:

The total project cost is determined by the quantity of work performed and the cost per unit of that work. For example, if it’s a painting job, the contractor might charge by square foot.

Project Types That Benefit From This Model:

This model works well for projects where tasks are repetitive and can be easily measured, like road construction or laying pipes. It’s less about the time spent and more about the amount of work done.


  • Fair Pricing: The owner pays only for the work that’s completed, which can feel fairer.
  • Scalability: The contract can easily adjust if the scope of the project increases or decreases.
  • Measurable: Since the work is paid per unit, it’s straightforward to see progress.


  • Estimation Risk: If the quantity needed is underestimated, costs can rise unexpectedly.
  • Oversight Needed: Owners need to monitor the count of units to ensure billing accuracy.
  • Variable Costs: The final cost can vary if the unit prices change due to market rates or other factors.

Get the Right Contract by Selecting the Best Construction Lawyer

Choosing the right type of construction contract is vital to the success of any building project. Each contract type, from Cost-Plus to Unit Price, offers its own balance of risks and rewards, transparency, and flexibility. These contracts serve as a critical roadmap, helping all parties navigate the complexities of construction, from skyscrapers to cosy homes.

However, having a contract is only half the battle. Ensuring that the contract protects your interests, addresses all project specifics, and complies with legal requirements is where a commercial contract lawyer becomes indispensable. An experienced construction lawyer can provide the necessary guidance to choose the right contract type, draft the fine details, and offer solutions that help avoid costly disputes. The significant surge in the financial impact of disputes in recent years only underscores the importance of getting it right.

Don’t risk the foundation of your project—invest in the right legal expertise to secure your construction’s future.

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