A construction contract is a legally binding agreement between a project owner and a contractor that sets out what work will be done, how much it will cost, and when it must be finished. Beyond those basics, it allocates risk, establishes the rules for handling surprises like hidden subsurface conditions or scope changes, and spells out how disputes get resolved. The type of contract you choose matters because it determines who absorbs the loss when costs run higher than expected, and the individual clauses determine how daily problems get handled once work begins.
What Makes a Construction Contract Legally Valid
A construction contract rests on the same legal foundations as any other enforceable agreement. If one of these elements is missing, a court can treat the whole document as void.
- Offer and acceptance. One party proposes specific terms and the other agrees to them. In construction, the owner usually solicits bids and the contractor submits one the owner accepts. Changing the price or timeline in the response creates a counteroffer, not a contract.
- Consideration. Each side gives something of value. The contractor provides labor and expertise; the owner provides payment. A promise without this exchange is not enforceable.1Legal Information Institute. Contract
- Capacity. Both parties must be legally able to enter a contract. For individuals, that means being of legal age and of sound mind. For businesses, the person signing must have authority to bind the company.1Legal Information Institute. Contract
- Lawful purpose. The contract cannot involve illegal activity. An agreement to build a structure that violates zoning laws or building codes on its face could be unenforceable.
Most construction contracts do not technically have to be in writing to be valid, but relying on an oral agreement is reckless. Written contracts protect both sides when memories differ, and many states require written agreements for residential work above a set dollar threshold.
Types of Construction Contracts
The contract type decides who bears financial risk when actual costs land above or below the estimate. No single type is universally better. The right choice depends on how clearly the scope is defined before anyone picks up a tool.
Lump Sum (Fixed Price)
The contractor agrees to complete the entire project for a single predetermined price. The owner knows the cost up front (barring change orders), and the contractor keeps any savings if actual costs come in under the bid. The contractor also absorbs any overruns. This structure works best when the design is complete and the scope is well defined, because the contractor needs accurate information to price risk. When the scope is fuzzy, bids get padded, and the owner pays for the uncertainty.
Cost-Plus
The owner reimburses the contractor for actual project costs, including labor, materials, equipment, and subcontractors, and pays an additional fee for overhead and profit. That fee can be a fixed dollar amount or a percentage of total costs. A fixed fee gives the owner more budget predictability. A percentage fee means the contractor earns more as costs rise, which creates an incentive problem worth watching. Cost-plus arrangements fit projects where the scope is not fully defined at the outset, but they demand open-book accounting and regular cost reporting.
Guaranteed Maximum Price (GMP)
A GMP contract is cost-plus with a ceiling. The contractor agrees to complete the project for no more than a stated maximum. If actual costs exceed the cap, the contractor eats the difference. If costs come in under, the contract usually specifies how the savings are shared. GMP contracts give owners protection against runaway costs while allowing cost-reimbursable flexibility during design. Contractors face real downside risk if they underestimate the GMP, so accurate early pricing matters.
Time and Materials
The contractor bills for hours worked at agreed rates plus the cost of materials. There is no cap and no fixed total. This approach is common for small-scope or emergency work where no one can predict the full extent of what is needed. Risk sits almost entirely with the owner, so these contracts often include a not-to-exceed amount as a rough spending limit.
Unit Price
The parties agree on a fixed price per measurable unit of work, such as per cubic yard of excavation or per linear foot of pipe. The total price depends on the actual quantities installed. Unit price contracts suit projects where the type of work is known but the quantities are not, which is common in civil and infrastructure work. The owner pays only for work actually performed, but the final number is uncertain until the job is done.
Choosing Between Them
The decision usually comes down to how complete the design is at signing. A finished design with clear specifications favors a lump sum, because the contractor can price it accurately. An evolving design or an unknown subsurface condition favors cost-plus or GMP, which let the work start before every detail is settled. Projects with known types of work but unknown quantities, like excavation or pipe installation, fit a unit price arrangement. Time and materials is the fallback when neither the scope nor the quantities can be predicted at all.
The Clauses That Decide What Happens When Things Go Wrong
The contract type sets the financial framework. The clauses below determine how specific problems get handled, and they are where most construction disputes are won or lost.
Scope of Work
The scope of work defines exactly what the contractor is responsible for delivering, including tasks, materials, quality standards, and project boundaries. A vague scope is the single most common source of construction disputes. If the scope does not clearly state whether the contractor handles site grading or permit fees, both sides will assume the other one does. Specificity here prevents arguments later.
Payment Terms and Retainage
Most construction contracts use progress payments tied to completed work rather than a single lump sum at the end. The owner or a representative like an architect reviews the work, certifies the amount completed, and authorizes payment.
Retainage is the portion of each progress payment the owner withholds until the project is finished. It gives the contractor a financial reason to close out punch-list items and finish properly. On federal construction contracts, retainage cannot exceed 10 percent of the approved payment amount and must be paid promptly once all contract requirements are met.2Acquisition.GOV. FAR 32.103 Progress Payments Under Construction Contracts Private contracts historically used 10 percent as well, though a growing number of states have capped retainage at 5 percent. Verify the rate and release conditions before signing.
Change Orders
Almost every project deviates from the original plans. A change order clause establishes how modifications to scope, schedule, or price get handled. A properly executed change order is a written document, signed by both parties, that describes the changed work and any adjustment to cost or timeline.
The common and expensive mistake is performing extra work on a verbal instruction without a signed change order. Most contracts require written approval, and a contractor who proceeds without it risks not being paid for the additional work. Courts have sometimes found that a pattern of accepting oral changes throughout a project can waive the written requirement, but counting on that is a gamble, not a strategy.
Liquidated Damages
A liquidated damages clause sets a predetermined dollar amount, usually charged per day, that the contractor owes if the project finishes late. These clauses exist because actual delay damages are often hard to calculate when the contract is signed. To be enforceable, the provision generally has to meet two conditions: the actual harm from a breach was genuinely difficult to estimate at signing, and the daily rate is a reasonable forecast of probable losses rather than an arbitrary penalty. Courts that find the amount unreasonable or punitive will refuse to enforce the clause. Contractors should push for a bonus for early completion if the contract imposes per-day penalties for delays.
Differing Site Conditions
Subsurface surprises are a fact of life. A differing site conditions clause allocates the cost of dealing with unexpected ground conditions. Standard contract forms recognize two categories. The first covers conditions that differ from what the contract documents indicated, such as hitting rock when the geotechnical report showed only soil. The second covers unusual conditions that no reasonable contractor would have expected for that type of work, regardless of what the documents said.3Acquisition.GOV. FAR 52.236-2 Differing Site Conditions
With this clause in place, the contractor has a path to additional compensation for genuinely unforeseeable conditions. Without it, the contractor generally bears the full risk, which is why fixed-price bids on sites with uncertain subsurface conditions tend to include heavy contingencies. Owners who strip the clause to shift risk often pay more through inflated bid prices.
Indemnification
Indemnification clauses decide who pays when a third party is injured or suffers property damage during the project. They come in three general forms. A broad-form clause requires one party (usually the contractor) to cover losses even when the other party is entirely at fault. An intermediate-form clause does the same unless the other party is solely responsible. A limited-form clause only requires indemnification to the extent of the indemnifying party’s own fault. The limited form is the most commonly enforceable version, because a majority of states have enacted anti-indemnity statutes that void broad-form clauses in construction contracts. Any indemnification provision should be reviewed by an attorney before signing.
Force Majeure
Force majeure clauses address events outside either party’s control, such as natural disasters, wars, government shutdowns, or pandemics that prevent or delay the work. The typical effect of a qualifying event is an extension of the timeline, not extra money. Some contract forms do allow cost recovery for certain force majeure events; many do not. Contractors who assume the clause automatically gives them both more time and more money are often disappointed when they read the fine print. Both parties should check exactly which events qualify and what relief is available.
Dispute Resolution
Construction disputes are common, and litigation is slow and expensive. Well-drafted contracts use a tiered process. The first step is usually direct negotiation between the project managers, escalating to senior executives if that fails. If informal resolution does not work, the contract typically requires mediation before either party can proceed to binding arbitration or litigation. Some contracts also provide for a dispute review board or project neutral who stays informed about the project and can issue non-binding recommendations quickly. This is one of the most overlooked provisions in a construction contract, which is unfortunate because it is also one of the most frequently used.
Termination
Construction contracts typically allow termination in two situations. Termination for default happens when one party fails to perform its obligations, such as a contractor who abandons the work or consistently delivers defective results. Termination for convenience allows the owner to end the contract for business reasons even when the contractor has done nothing wrong. The consequences differ. A default termination can leave the contractor liable for the cost of completing the work with a replacement. A convenience termination entitles the contractor to payment for work completed and, in many contracts, lost anticipated profit on the unperformed portion.
Substantial Completion and Warranties
A project reaches substantial completion when the owner can use the building or structure for its intended purpose, even if minor punch-list items remain. This milestone matters because it typically triggers several events: the owner takes possession, warranty periods begin, retainage release may be initiated, and liquidated damages for delay stop accruing. Final completion occurs only when every punch-list item is corrected and all contract obligations are satisfied.4Acquisition.GOV. GSA 552.211-70 Substantial Completion
Every contractor carries an implied warranty that work will be performed in a competent manner and will be reasonably free of major defects. This warranty exists by operation of law in most states, regardless of whether the contract mentions it. It covers the quality of the contractor’s labor and installation but generally does not extend to defects in materials themselves. Express warranties in the contract may add protections, such as a one-year callback period during which the contractor must repair defective work at no cost. Confirm what warranty coverage the contract provides and how long it lasts before signing.
Bonds and Payment Protection
Large sums flow through construction projects across multiple layers of contractors and suppliers, and payment disputes can shut a job down entirely. Two mechanisms protect against that risk.
Performance and Payment Bonds
A performance bond guarantees that the contractor will complete the project according to the contract terms. If the contractor defaults, the surety company that issued the bond steps in to arrange completion. A payment bond guarantees that subcontractors and material suppliers will be paid. Federal law requires both types of bonds on any government construction contract exceeding $100,000.5Office of the Law Revision Counsel. 40 USC 3131 Bonds of Contractors of Public Buildings or Works Most states impose similar requirements for state and local public projects, though dollar thresholds vary. Private projects may or may not require bonds depending on the contract terms and the lender’s requirements.
Mechanic’s Liens
A mechanic’s lien gives a contractor, subcontractor, or supplier the right to place a legal claim against the property itself when they are not paid for their work. If the lien is not resolved, the lienholder can ultimately force a sale of the property to collect what is owed. Every state has a mechanic’s lien statute, but the rules differ significantly on who qualifies, what notices must be sent, and how quickly the lien must be filed after the last day of work. Filing deadlines range from as little as 30 days to several months depending on the state. Missing the deadline forfeits the lien right entirely, which is why tracking these dates is not optional for anyone performing construction work.
Licensing: The Threshold That Can Void Everything Else
Most states require contractors to hold a license before performing construction work, and the consequences of working without one go beyond fines. In many jurisdictions, an unlicensed contractor cannot sue for payment even if the work was completed perfectly. Some states allow the owner to recover every dollar paid to an unlicensed contractor, which means the contractor does the work, receives nothing, and has no legal remedy. Criminal penalties for unlicensed contracting also exist in many states, with fines and potential jail time for repeat offenders.
For owners, hiring an unlicensed contractor means forfeiting most legal protections. Insurance coverage, warranty claims, and bond protections may all be void if the contractor was not properly licensed. Before signing any construction contract, verify the contractor’s license status through the state licensing board.