Types of Construction Contracts: The 4 Most Common

Every construction project runs on a contract. Before work starts, the owner and contractor agree on what gets built, what it costs, and who pays for surprises. The types of construction contracts differ mainly in how they answer that last question.

Most owners focus on the bottom-line price. The contract type matters just as much. Two contractors can quote the same number and still leave you with very different risks. The difference is in how that number is built, billed, and paid.

This guide explains the four most common types of construction contracts in plain language. It covers how each one works, which projects it fits, and where the risks hide. It also covers how specialty trades bid and bill, and how each contract holds up in a dispute. Finally, it shows how project size and complexity point to the right choice.

What Does a Construction Contract Do?

A construction contract is a legally binding agreement between the person paying for the work and the company doing it. It turns a set of plans into enforceable promises.

A few terms come up throughout this guide:

Owner:

The person or company paying for the project. This could be a homeowner, a small business, a startup, or a developer.

General Contractor (GC):

The company the owner hires to build the whole project. The GC manages the schedule, the site, and the trades.

Trades (Subcontractors):

Specialty companies the GC hires for one part of the work. Examples include electricians, plumbers, roofers, and drywall installers.

Scope of Work:

The exact work activities being paid for, as defined by the drawings and specifications. “Install 24 feet of base cabinets and a quartz countertop” is a scope. “Redo the kitchen” is not.

Whatever its type, a construction contract typically spells out:

1. The scope of work
2. The price, and how that price is calculated
3. The schedule, including start and completion dates
4. How often the contractor can bill, and how much the owner holds back from each payment. That holdback is called retainage. It is commonly 5 to 10 percent until the job is finished.
5. How changes are requested, priced, and approved. A change order is a signed amendment that adds, removes, or alters work.
6. Who pays for unexpected problems, such as buried rock, price spikes, or hidden damage in an old building
7. How disputes are resolved

Most of the rules for how the owner and contractor work together sit in the general conditions of the contract. The contract type is chosen in the agreement form itself. For example, the American Institute of Architects (AIA) publishes a separate owner-contractor agreement for each major pricing method:

• Document AIA A101: Lump sum, which AIA calls a “stipulated sum”
• Document AIA A102: Cost of the work plus a fee, with a guaranteed maximum price
• Document AIA A103: Cost of the work plus a fee, without a guaranteed maximum price

Time and material and unit price work are usually handled through custom contracts. Standard lump sum forms also include a section for listing unit prices.

Why Are There Different Types of Construction Contracts?

Every project has unknowns. Soil conditions, hidden damage, material prices, weather, and design changes can all move the final cost. The main job of any contract type is to decide who carries those risks.

A contractor who knows exactly what it is building can safely promise a fixed price. A contractor facing big unknowns cannot. It will either add a large cushion to its price or ask the owner to share the risk.

An everyday comparison helps. Think about the different ways people pay for services:

LUMP SUM:

This is like buying a new car at an agreed price. You know the total “bottom line, out the door price” before you sign.

COST-PLUS:

A cost-plus contract is like hiring a wedding planner who passes along every vendor receipt, plus a planning fee.

TIME & MATERIAL:

This type of contract is like paying a mechanic by the hour to track down a strange noise in your engine.

UNIT PRICE:

Compare this to buying gas. The price per gallon is set, but the total depends on how much you pump.

Several factors decide which approach makes sense for a project:

• Design completeness: Are the drawings finished, or still being developed?
• Hidden conditions: Is this new construction on a clear site, or a remodel of an old building?
• Speed: Does work need to start before the design is done, or right away in an emergency?
• Budget certainty: Does the owner or its lender need a firm number before work begins?
• Owner involvement: Does the owner have the time or staff to review invoices, time sheets, and receipts?

Construction lenders, for example, usually want to see either a fixed price or a guaranteed maximum price before they fund a loan. They want to know the project can be finished with the money available.

The four types of construction contracts covered below are the most common in the United States. Each one handles price and risk in a different way. Many projects combine more than one type, which is covered later in this guide.

#1 – Lump Sum (Fixed Price) Contracts

How a Lump Sum Contract Works

In a lump sum contract, the contractor agrees to build a defined scope of work for one fixed price. It is also called a fixed price or stipulated sum contract.

That price includes everything the contractor expects to spend. It covers labor, materials, equipment, subcontracts, job overhead, and profit. It also includes a cushion for the risks the contractor is taking on.

The owner does not see the contractor’s actual costs. If the job costs less than expected, the contractor keeps the difference. If it costs more, the contractor absorbs the loss.

The price only changes through a change order. That happens when the owner adds or removes work, or when conditions differ from what the contract documents described.

Lump sum work is usually competitively bid. Several contractors price the same set of drawings, and the owner compares the totals. The owner then weighs price alongside references, experience, and schedule.

Best Projects for a Lump Sum Contract

A lump sum contract works best when the contractor can price the work with confidence. Good fits include:

• New buildings with complete drawings and specifications
• Remodels where existing conditions are simple and easy to see, such as a kitchen update in a newer home
• Tenant build-outs in empty commercial space, where the drawings define every wall and finish
• Projects where the owner wants to compare several bids on the same drawings
• Any project where the owner or lender needs a firm number before work starts

It is a poor fit when the design is unfinished or when much of the work is hidden. Pricing a remodel of a 90-year-old building as lump sum often leads to a long list of change orders.

Risks of a Lump Sum Contract

For the owner, the main risks are:

• Change orders cost more. Once the contract is signed, there is no competition. The contractor prices each change without another bidder to compare against.
• Incomplete drawings become change orders. Anything missing or unclear in the documents can turn into an added cost.
• Hidden padding. Contractors add money to cover risk called contingency. The owner pays that cushion whether or not the risk ever shows up.
• Pressure on quality. A contractor who bid too low may cut corners or push hard for change orders to recover its losses.

For the contractor, the main risks are:

• Estimating mistakes, which come straight out of profit
• Rising material and labor prices after the bid
• Crews that work slower than planned
• Weather and other delays that stretch job overhead costs

Of all the types of construction contracts, lump sum shifts the most cost risk to the contractor. That is why the scope must be clear. A contractor can only guarantee a price for work it can see.

Real World Example: A Café Build-Out

#2 – Cost-Plus Contracts

How a Cost-Plus Contract Works

In a cost-plus contract, the owner pays the contractor’s actual costs, plus a fee. The fee covers the contractor’s home office overhead and profit.

The contract must define exactly what counts as a reimbursable cost. That usually includes:

• Wages and payroll costs for workers and project staff
• Materials and equipment used on the project
• Payments to subcontractors
• Job-site overhead, such as trailers, temporary power, and cleanup

It is an open-book arrangement. The owner receives copies of invoices, payroll records, and receipts. The owner usually has the right to audit the contractor’s records.

Cost-plus contracts come in three main forms:

Cost Plus a Percentage Fee:

The fee is a percentage of the total cost. The more the project costs, the more the contractor earns. That is why many owners avoid this version or pair it with a cap.

Cost Plus a Fixed Fee:

The fee is a set dollar amount agreed up front. The contractor earns the same fee whether costs rise or fall.

Cost Plus a Fee with a Guaranteed Maximum Price (GMP):

The owner pays actual costs and the fee, up to a cap. If costs go over the cap, the contractor pays the overage unless the owner changed the scope.

Many GMP contracts include a shared savings clause. If the final cost comes in under the cap, the owner and contractor split the savings. Common splits are 50/50 or weighted toward the owner, such as 70/30.

Fees vary by project. With smaller residential and commercial work, fees of 10 to 20 percent are common. On large commercial projects, fees are often much lower as a percentage, because the dollar amounts are so large.

With larger projects, the contractor is often hired while the design is still underway. This arrangement is called construction manager at risk. During design, the contractor helps with pricing and planning. Once the drawings are far enough along, it commits to a GMP.

Best Projects for a Cost-Plus Contract

• Projects that must start before the design is finished, often called fast-track projects
• Renovations of older buildings where the condition behind the walls is unknown
• Custom homes where the owner is still choosing finishes as work progresses
• Large or complex buildings, such as medical offices, labs, and hotels, where a GMP gives cost protection before the design is final
• Owners who have the staff or consultants to review costs every month

Risks of a Cost-Plus Contract

For the owner, the main risks are:

• No final price – Without a GMP, the owner does not know the total until the project is finished.
• Weak cost control – Without a cap or a fixed fee, the contractor has little reason to save money.
• Paperwork – Someone must review invoices, payroll, and receipts every month. That takes time or a paid consultant.
• Disputes over what counts as cost – Gray areas include staff who split time between jobs, company-owned equipment, and rework to fix mistakes.
• A GMP has limits – The cap goes up when the owner adds scope. It also usually contains a contractor contingency, which the owner is paying for.

For the contractor, the main risks are:

• Costs above a GMP that it cannot tie to an owner change
• Costs an owner’s auditor rejects as not reimbursable
• Heavy record-keeping requirements

Real World Example: An Outpatient Clinic Expansion

#3 – Time and Material Contracts

How a Time and Material Contract Works

In a time and material (T&M) contract, the owner pays for the hours worked and the materials used. There is no fixed price for the finished job.

The contract sets the rates in advance:

• Hourly labor rates: A set rate for each worker type, such as foreman, journeyman (a fully trained tradesperson), and apprentice. These rates are usually “loaded.” That means they include wages, payroll taxes, insurance, benefits, overhead, and profit.
• Materials: Billed at actual cost plus a markup. Markups of 10 to 30 percent are common, so this number is worth negotiating.
• Equipment: Billed at set hourly or daily rates for items like lifts, excavators, and generators.

The key record is the daily time ticket. It lists each worker, the hours worked, the materials installed, and the equipment used that day. The owner’s representative should review and sign each ticket daily.

Most T&M contracts also include a not-to-exceed (NTE) amount. The contractor cannot bill past that ceiling without written approval. An owner should never sign a T&M agreement without one.

Of all the types of construction contracts, T&M has the least built-in cost control.

Best Projects for a Time and Material Contract

• Emergency repairs, such as storm, fire, or water damage, where work must start immediately
• Small jobs where the scope cannot be defined until work begins, such as opening a wall to trace a leak
• Exploratory demolition to find out what is behind walls or under floors
• Small changes on a larger project that are hard to price in advance
• Ongoing maintenance and service work

T&M is rarely a good choice for an entire building. It works best on short, contained jobs that the owner can watch closely.

Risks of a Time and Material Contract

For the owner, the main risks are:

• No reward for speed. A slow crew earns more than a fast one.
• Hours are hard to verify. If no one from the owner’s side is on site, the owner is simply trusting the tickets.
• Late signatures. Tickets signed days or weeks after the work are much harder to check.
• Budget creep. Small jobs can grow when the contractor keeps finding “one more thing.”

For the contractor, the main risks are:

• Unsigned tickets the owner refuses to pay
• Work past the NTE amount that was not approved in writing
• Lower profit than a well-run lump sum job could earn

Real World Example: Emergency Roof Repair After a Windstorm

#4 – Unit Price Contracts

How a Unit Price Contract Works

In a unit price contract, the owner pays a set price for each unit of work installed. A unit is any measurable quantity. Common examples include:

• Cubic yards of soil or rock excavated
• Linear feet of pipe installed
• Tons of asphalt placed
• Square yards of paving or square feet of sidewalk
• Each manhole, fire hydrant, or light pole

The owner’s engineer prepares a bid form listing every item with an estimated quantity. Contractors fill in a price for each unit. To compare bids, the owner multiplies each unit price by its estimated quantity and adds up the totals.

The owner then pays for the actual quantities installed, not the estimates. Quantities are verified by field measurement, surveys, or delivery tickets. For example, each truckload of asphalt arrives with a weight ticket from the plant.

Estimates are rarely exact. Many unit price contracts include a variation in quantities clause. If an actual quantity differs from the estimate by more than a set percentage, either side can request a price adjustment.

The contract sets that threshold. Thresholds between 15 and 25 percent above or below the estimate are common.

Why adjust at all? Part of a contractor’s cost is fixed, such as moving equipment to the site. If quantities drop sharply, those fixed costs are spread over fewer units. If quantities soar, the contractor may recover those fixed costs many times over.

Best Projects for a Unit Price Contract

• Private roads and drives inside a new development or business park
• Site utilities, such as water, sewer, and storm drain lines serving a development
• Earthwork, grading, and rock excavation
• Parking lots, sidewalks, and curbs
• Subdivision and commercial site work

Unit prices also show up inside other contract types. A lump sum contract may list unit prices for extra rock excavation or replacing unsuitable soil. Unsuitable soil is ground too soft or unstable to support the work. Setting these prices up front avoids arguments when the quantity turns out larger than expected.

Risks of a Unit Price Contract

For the owner, the main risks are:

• No final price until the work is measured. The total depends on the actual quantities.
• Bad estimates. If the engineer’s quantities are wrong, the budget is wrong too.
• Unbalanced bidding. A contractor may inflate prices on items it expects to overrun and cut prices on the rest. Its total looks competitive, but the final bill climbs as quantities grow.
• Measurement disputes. Both sides must agree on how and when each unit is measured.

For the contractor, the main risks are:

• Quantities far below the estimate, leaving fixed costs unrecovered
• Slower production than planned, such as rock that is harder to dig than expected
• Measurement disputes that delay payment

Real World Example: Hard Caliche Under a New Subdivision

How Trades Bid to General Contractors Under Each Contract Type

On most commercial projects, the general contractor does not perform most of the work itself. Specialty trades handle the concrete, framing, plumbing, electrical, roofing, and finishes. The GC collects bids from those trades and builds its own price from them.

Here is a point many owners miss. The GC’s contract with the owner and the GC’s contracts with its trades do not have to match. An owner can sign a T&M contract with a GC, while the GC holds lump sum contracts with its trades. That mismatch is where risk quietly shifts.

Trade Bids Under a Lump Sum Contract

When the GC is bidding a lump sum job, it sends each trade a bid package. That package includes the drawings, specifications, and a description of the trade’s scope.

Each trade returns one lump sum price for its scope. A typical trade bid also lists:

• Inclusions: What the price covers, such as “all rough-in and trim for 32 light fixtures”
• Exclusions: What the price does not cover, such as permits, patching, or after-hours work
• Alternates: Separate prices for optional upgrades or deductions the owner may choose
• Unit prices: Rates for extra work, such as a cost per added outlet

GCs typically aim for at least three bids per trade. They then line the bids up side by side, a process called bid leveling. This confirms each bid covers the same scope before the prices are compared.

A low bid that excludes half the work is not really low. Bid leveling catches that. The GC then adds its own costs, overhead, and profit to reach its lump sum price.

Trade Bids Under a Cost-Plus Contract

Under a cost-plus contract, trades still usually bid lump sum. The difference is who sees the bids and who keeps the savings.

Because the arrangement is open book, the owner can typically review every trade bid. Many cost-plus contracts give the owner the right to approve which trade is selected. Some require the GC to explain in writing if it does not choose the lowest qualified bidder.

Awarding these subcontracts is called the buyout. Under cost-plus, the owner pays the actual subcontract amounts. If the buyout comes in under budget, those savings belong to the owner. Under a GMP, they typically go into the shared savings pool.

Any work the GC performs with its own crews is billed at actual cost. That usually includes wages, payroll costs, materials, and equipment.

Trade Bids Under a Time and Material Contract

Under a T&M contract, the GC asks each trade for a rate sheet instead of a total price. A rate sheet usually includes:

• Hourly rates for each worker classification, such as foreman, journeyman, and apprentice
• Overtime and weekend rates
• The markup the trade will add to materials
• Hourly or daily rates for the trade’s equipment

The GC may also ask each trade for its own not-to-exceed amount. That helps the GC stay under the NTE in its contract with the owner.

Trade Bids Under a Unit Price Contract

Under a unit price contract, trades usually bid unit prices that match the owner’s bid form. For example, a utility trade might bid a price per linear foot of sewer pipe and a price per manhole.

The GC adds its markup to each trade’s unit price. The result becomes the GC’s unit price on the owner’s bid form. When the trade’s pricing matches the owner’s units, the payment chain lines up cleanly.

How Trades Invoice Under Each Contract Type

Most projects bill on a monthly cycle. Each trade sends its pay request to the GC by a set day of the month. The GC combines those requests with its own costs into one pay application to the owner.

A pay application is the formal monthly invoice on a construction project. On many private commercial jobs, it follows the AIA G702 and G703 forms. The G702 is the summary page, and the G703 lists each line item.

Two things travel with every payment, whatever the contract type:

• Retainage: The percentage held back from each payment until the work is complete. The owner holds it from the GC, and the GC typically holds it from each trade.
• Lien waivers: Signed documents in which the GC or trade gives up its right to file a lien for the amount paid. A lien is a legal claim against the property for unpaid work.

Invoicing Under a Lump Sum Contract

Each trade breaks its lump sum into a schedule of values. This is a list of line items that add up to the total price. An electrical schedule of values might look like this:

• Mobilization: $4,000
• Underground conduit: $18,000
• Rough-in: $42,000
• Panels and switchgear: $26,000
• Fixtures and trim: $30,000

Each month, the trade bills the percent complete for each line. If rough-in is half done, the trade bills $21,000 for that line. The GC’s superintendent checks the work in the field before approving the request.

Watch for front-loading. That happens when a trade or GC puts too much value on early line items to get paid sooner. It leaves too little money for the remaining work if the contractor walks away.

Invoicing Under a Cost-Plus Contract

Trades bill the GC the same way they would on a lump sum job, by percent complete against their schedule of values. The difference is in how the GC bills the owner.

The GC bills its actual costs for the month, plus its fee. The pay application usually includes backup such as:

1. Copies of each trade’s approved pay request
2. Payroll records for the GC’s own crews and project staff
3. Material invoices and equipment rental receipts
4. Job-site overhead costs, such as trailer rent and temporary utilities

The owner, or a consultant working for the owner, reviews this backup before paying. Anything without support can be held until the GC provides it.

Invoicing Under a Time and Material Contract

Each trade bills the GC for its hours, materials, and equipment at the agreed rates. The invoice should include the signed daily tickets and material receipts.

The GC checks each ticket against its own daily logs. It then adds its markup and bills the owner. Tickets that no one signed are the first ones an owner will question.

Invoicing Under a Unit Price Contract

Each month, the trade bills for the units installed that month, multiplied by its unit price. For example, 400 linear feet of pipe at $62 per foot equals $24,800.

Quantities are usually confirmed jointly by the trade, the GC, and the owner’s engineer. Field measurements, survey data, and delivery tickets serve as proof.

What Happens When a Trade Bids Lump Sum Under a T&M or Unit Price Contract?

Under lump sum and cost-plus contracts, lump sum trade bids are normal. The friction shows up under T&M and unit price contracts.

Many trades refuse to break out their costs. Some want to protect their pricing from competitors. Others do not want the extra paperwork of daily tickets or unit tracking. Many simply price all their work as a lump sum and will not change that for one job.

The GC then has a choice. It can find another trade, negotiate, or accept the lump sum bid. If it accepts, the risk on that scope shifts in ways the owner should understand.

Lump Sum Trade Bids Under a T&M Contract

When a trade prices its work as a lump sum inside a T&M contract, that one scope behaves like a small fixed-price job. The risk shifts like this:

• The trade carries its own cost risk. If its work takes longer than planned, the trade absorbs the extra cost.
• The owner loses any savings. If the work goes faster than planned, the owner still pays the full lump sum.
• The owner loses visibility. There are no hours or material receipts to review for that scope.
• The billing backup changes. The owner’s contract may require time tickets for all work. A lump sum trade cannot produce them.

Under T&M, the GC generally does not convert the lump sum into hours. There is no honest way to do that without the trade’s real labor data. Instead, the GC treats the lump sum as a subcontract cost.

How the GC Passes Through a Lump Sum Trade Bid Under a T&M Contract

A careful GC gets the owner’s written approval before awarding a lump sum subcontract under a T&M contract. Once approved, the pass-through usually works like this:

1. The subcontract gets its own line on the GC’s pay application, listed as a lump sum.
2. The trade provides a schedule of values for its lump sum.
3. Each month, the GC bills the owner the trade’s percent complete, verified in the field.
4. The trade’s invoice and lien waiver replace time tickets as backup.
5. The GC adds the markup its contract allows on subcontracted work. Many T&M contracts set a lower markup on subcontracts than on the GC’s own labor.
6. Retainage applies to the line like any other.

Real World Example: Fire Sprinkler Work in a T&M Office Repair

Lump Sum Trade Bids Under a Unit Price Contract

Under a unit price contract, the mismatch is sharper. The owner pays the GC for each unit measured. The GC owes the trade one fixed amount, no matter how many units are installed.

That leaves the quantity risk with the GC:

• If quantities come in high, the owner pays the GC more. The GC still pays the trade the same lump sum, so the GC gains and the trade absorbs the extra work.
• If quantities come in low, the owner pays the GC less. The GC still owes the trade the full lump sum, so the GC loses money.

One exception matters. If the owner changes the scope, the trade will ask for a change order. The quantity risk only covers variations within the original scope.

So does the GC convert the lump sum into a unit price? For bidding, yes. The GC divides the trade’s lump sum by the owner’s estimated quantity. That gives an implied cost per unit. The GC adds its markup and enters the result on the owner’s bid form.

For billing, the two sides of the chain work differently:

• GC to owner: The GC bills measured quantities at its unit price, like every other item on the contract. It does not bill by percent complete.
• Trade to GC: The trade bills by percent complete against its lump sum schedule of values.

The gap between those two methods is the GC’s risk. Experienced GCs try to close it. They may ask the trade for add and deduct unit rates for quantity changes. Others build a cushion into their unit price to cover the exposure.

Real World Example: Asphalt Paving Priced by the Ton

What Owners Should Require for Lump Sum Trade Bids

Owners using T&M or unit price contracts can protect themselves with a few simple requirements:

1. Require written notice before the GC awards any lump sum subcontract.
2. Approve each lump sum subcontract in writing before work starts.
3. Ask for at least one competing quote to confirm the price is fair.
4. Require a schedule of values for each lump sum subcontract.
5. Confirm the GC’s markup on subcontracted work before signing.
6. Collect a lien waiver from each trade with every payment.
7. On unit price jobs, ask which major items the GC is subcontracting and how those trades priced them.

None of the types of construction contracts prevents lump sum trade bids. Written approval simply keeps the owner from being surprised by them.

How Each Type of Construction Contract Holds Up in a Dispute

Any contract can end up in a dispute. Most construction contracts set out the process, which usually starts with negotiation and moves to mediation. Mediation is a meeting where a neutral third party helps both sides reach a settlement. If that fails, the dispute goes to arbitration or court.

That process is the same across the types of construction contracts. What changes is what the fight is about and which records decide it.

Lump Sum Disputes: What Was Included?

Lump sum disputes almost always come down to scope. The contractor says a piece of work was extra. The owner says it was already in the price. Common examples include:

• Extra work claims: Work the contractor believes was not shown in the drawings or specifications
• Differing site conditions: Conditions that are very different from what the contract documents showed, such as buried debris not noted in the soils report
• Delay claims: Requests for more time and money when the owner or its designers slowed the work

The key evidence is the contract documents themselves. Drawings, specifications, signed change orders, and RFIs all matter. An RFI, or request for information, is a formal written question from the contractor to the design team.

It holds up well when the documents are complete. A clear scope gives the owner a strong position on the base price. Vague or incomplete drawings weaken it, because unclear language is often read against the party who wrote it.

Cost-Plus Disputes: What Counts as a Cost?

Cost-plus disputes focus on money that has already been spent. The common questions are:

1. Was this cost allowed under the contract’s definition of reimbursable cost?
2. Was it reasonable and necessary for the project?
3. Should this change raise the GMP, or was it already covered?
4. Was the contractor’s contingency used properly?
5. How should the savings be split at the end?

The key evidence is the accounting record: payroll, invoices, receipts, and cost reports. Disputes often require forensic accountants, who are specialists in tracing and auditing project costs. That makes them expensive to resolve.

How it holds up depends on the cap. With a GMP, the owner has a firm ceiling to point to. Without one, the owner usually must prove a cost was improper, which is a hard burden. Owners who never used their audit rights during the job have the weakest position.

Time and Material Disputes: Were the Hours Real?

T&M disputes center on hours, crew size, and efficiency. The owner questions whether the work took as long as billed. The contractor points to the daily tickets.

Signed tickets are strong evidence for the contractor. Once an owner’s representative signs, disputing those hours later is difficult. Unsigned tickets, or tickets signed weeks late, are much weaker. Work past the NTE without written approval is often the contractor’s loss.

A practical tip for owners: sign tickets with a note such as “time and materials verified only.” That confirms the hours and materials without agreeing the work was extra or necessary.

How it holds up depends almost entirely on the daily records. The side with better documentation usually wins.

Unit Price Disputes: How Many Units?

Unit price disputes focus on measurement. The questions are how many units were installed and how they were measured. Other common issues include:

• Requests for new unit prices under the variation in quantities clause
• Whether a quantity change came from normal variation or an owner change
• Unbalanced bids that produce a large final bill

The key evidence is survey data, field measurements, and delivery tickets. Many of these records are created by third parties, such as surveyors or material plants.

How it holds up is usually the most objective of the four. Units can be counted or measured, so disputes tend to be narrower. The biggest risk is failing to agree on the measurement method before work starts.

How Project Size and Complexity Affect the Type of Construction Contract

Three factors shape which contract type is most effective and least risky:

Size:

Bigger projects carry bigger dollar risks. A 5 percent overrun on a $50,000 remodel is $2,500. On a $50 million building, it is $2.5 million.

Complexity:

This includes the number of trades, specialized systems, hidden conditions, and whether the building is occupied during work.

Total Budget:

How much money is at stake, and how firmly the owner or lender needs it capped.

A simple rule of thumb applies. Smaller, simpler projects with clear scopes suit lump sum contracts. Larger, more complex projects lean toward cost-plus with a GMP. T&M fits small, uncertain pieces of work. Unit price fits measurable site work at almost any size.

The size ranges below are rough guides, not industry standards. Definitions vary by region and by who is doing the defining.

Small Projects (Under $1 Million)

Small projects include kitchen and bath remodels, home additions, small tenant build-outs, and repairs. The most common contract types are:

• Lump sum for remodels and build-outs with a clear scope
• T&M with an NTE for repairs and jobs with hidden conditions
• Cost plus a fixed fee for high-end remodels where the owner is still choosing finishes

The biggest risk on small projects is a thin scope. Many residential jobs have no architect’s drawings. The contractor’s written proposal becomes the scope, so it must be specific.

Small lump sum contracts often include an allowance. An allowance is a set dollar amount for an item not yet selected or not yet known. If the actual cost is higher, the owner pays the difference. If it is lower, the owner gets a credit.

Mid-Size Projects ($1 Million to $25 Million)

Mid-size projects include small office buildings, restaurants built from the ground up, medical offices, warehouses, and small apartment buildings. The most common contract types are:

• Lump sum when the design is complete and the owner wants competitive bids
• Cost-plus with a GMP when the owner needs to start before the design is finished
• Unit prices inside either contract for uncertain site work, such as rock or poor soils

At this size, most owners have an architect and a construction lender. The lender will usually require either a lump sum or a GMP. Many owners also hire an owner’s representative, a consultant who manages the project on the owner’s behalf.

Large Projects ($25 Million to $1 Billion)

Large projects include hotels, hospitals, high-rise offices, large apartment complexes, and corporate campuses. The most common contract types are:

• Cost-plus with a GMP, usually with a construction manager at risk hired during design
• Lump sum trade contracts bought out by the construction manager under the GMP
• Unit prices for site work and T&M for small changes

At this size, design and construction often overlap to save time. Foundations may be poured while interior finishes are still being designed. A lump sum price is hard to set under those conditions.

Lump sum contracts are still used on large projects with complete designs. But the more complex the building, the more change orders a lump sum contract tends to produce.

Mega Projects (Over $1 Billion)

Mega projects include data center campuses, semiconductor plants, and large resort developments. At this size, no single contract type fits the whole job. Most mega projects use all four types at once.

• GMP contracts for each building or phase, priced as its design is completed
• Unit price contracts for mass grading, roads, and utilities across the site
• Lump sum contracts for well-defined packages, such as parking structures or support buildings
• T&M contracts for owner-directed work that cannot be priced in advance

A single lump sum for an entire mega project is rare. Few contractors can carry that much risk, and even fewer can obtain bonds large enough to cover it.

Mega projects also run for years, so material prices can move a lot. Many contracts include escalation clauses. An escalation clause adjusts the price if certain material costs rise or fall beyond a set amount.

Types of Construction Contracts at a Glance

Contract Type	Owner Pays	Cost Risk Mostly On	Best For
Lump Sum	One fixed price	Contractor	Complete designs and clear scopes
Cost-Plus	Actual costs plus a fee	Owner (shared with a GMP)	Unfinished designs and complex buildings
Time and Material	Hours, materials, and markup	Owner	Emergencies and small unknown jobs
Unit Price	Price per measured unit	Shared: owner on quantity, contractor on unit cost	Site work and measurable quantities

Choosing Among the Types of Construction Contracts

No contract type is best for every project. The right choice depends on how much is known when the contract is signed. The more certain the scope, the more risk a contractor can safely take on.

Before signing any construction contract, ask these questions:

1. How complete are the drawings and specifications?
2. What hidden conditions could change the cost?
3. Who pays if those conditions show up?
4. Is there a ceiling on the total price, and what moves it?
5. How will the contractor bill, and what backup comes with each invoice?
6. How are the trades pricing their work, and does that match the contract type?
7. Does the owner have the time or help to review costs, tickets, or quantities?

The answers will usually point to the right contract type. On many projects, they will point to more than one.