Understanding Construction Contracts

The conversation that surprises homeowners most, in my experience, is the one where I explain that "construction contract" is not a single thing. It is a family of pricing structures, and the structure the parties choose determines who absorbs which risks during construction. The clause that scares a homeowner in one structure is normal and necessary in another. Before reading any specific contract, it helps to understand which family the contract belongs to — because the right question to ask depends on the family.

This article is the orientation conversation. It does not catalogue every clause; it sketches the four common structures and explains, in plain terms, what each one means for a Colorado residential owner.

Why structure matters more than length

Owners often judge contracts by length: a thirty-page document feels safer than a five-page document. Length is a poor proxy. What actually controls the economic outcome of a project is how the parties have agreed to price it, and what happens when the project departs from the assumptions baked into the price. A short, clean lump-sum contract for a modest remodel can produce excellent outcomes. A long, elaborate cost-plus contract with vague controls can produce ruinous overruns. The structure is the engine; the words are the bodywork.

Structure one: lump-sum (fixed-price)

In a lump-sum contract, the contractor agrees to perform a defined scope of work for a single fixed price. The owner pays the agreed sum on a milestone schedule regardless of what the contractor's actual costs turn out to be. If the contractor's costs come in low, the contractor keeps the difference as profit; if they come in high, the contractor absorbs the loss.

What lump-sum buys the owner: pricing certainty. The total exposure is known on day one, subject only to formal change orders. What it costs the owner: the contractor will price contingencies into the lump sum to protect against unknowns, so the owner pays for risks that may never materialize.

Lump-sum works best when the scope is well-defined — typically when complete plans and specifications are in hand before bidding — and when the project does not involve substantial discovery work (such as opening walls in an older home where conditions are unknown).

Structure two: cost-plus

In a cost-plus contract, the owner pays the contractor's actual costs (labor, materials, subcontractor invoices) plus an agreed fee. The fee is sometimes a percentage of cost, sometimes a fixed amount, and sometimes a hybrid. The owner sees real invoices and pays for what was actually spent.

What cost-plus buys the owner: pricing follows reality. If the project comes in below initial estimates, the owner captures the saving. The contractor has no incentive to inflate a lump-sum bid because there is no lump-sum bid. What it costs the owner: the owner absorbs the risk of overruns, and a percentage-fee structure can subtly incentivize the contractor to let costs grow, since the contractor's fee grows with them. The discipline of cost-plus depends on rigorous documentation of costs and active owner oversight.

Cost-plus works best when scope is uncertain at the outset — substantial renovations to older homes, projects with evolving design, or jobs where the owner wants flexibility to make decisions as construction progresses.

Structure three: time-and-materials (T&M)

Time-and-materials is the close cousin of cost-plus, but with the contractor's labor billed at a fixed hourly rate that includes their overhead and profit, and materials billed at cost or at a small markup. It is the structure most common on small jobs — a kitchen plumbing replacement, a deck rebuild — where the work is not large enough to justify the overhead of a formal cost-plus accounting.

What T&M buys the owner: simplicity and flexibility on small jobs. What it costs the owner: no price cap. A small T&M job can outgrow its initial scope very quickly if the homeowner is not paying attention.

T&M works best when the job is bounded by the physical scope (replace this specific component) and when the homeowner is engaged enough to monitor progress and approve material purchases.

Structure four: guaranteed maximum price (GMP)

A GMP contract is structurally a cost-plus contract with a ceiling. The contractor bills actual costs plus the agreed fee, but the total cannot exceed the guaranteed maximum, except for owner-approved change orders. If actual costs come in below the GMP, the parties share the savings according to an agreed split.

What GMP buys the owner: the upside flexibility of cost-plus combined with the downside certainty of lump-sum. What it costs the owner: GMPs are complex to draft and administer, and the GMP price typically includes a contractor contingency that the owner pays for whether or not the contingency is consumed. GMPs are mostly seen on larger residential projects and on commercial work; they are uncommon on small remodels.

Which structure for which project

There is no universally correct answer, but a rough heuristic is useful:

• Defined scope with complete plans → lump-sum.

• Substantial unknowns or evolving design → cost-plus with strong documentation discipline.

• Small bounded jobs → time-and-materials.

• Larger residential or hybrid projects → GMP, when the parties have the sophistication to administer it.

The structure should match the certainty of the scope. Forcing a lump-sum bid on a project with significant unknowns invites overpricing (because the contractor must price the risk) and dispute (because the unknowns will surface as change orders the contractor needs to recover for).

Where the legal pressure points sit, by structure

Different structures generate different categories of dispute, and a contract appropriate for one structure can be inappropriate for another. A few examples:

• Change orders matter most in lump-sum contracts, because every departure from the original scope must be priced and approved through that mechanism. The Colorado practitioner literature on change-order documentation is well developed; I have written about it separately. In cost-plus and T&M, change orders are less critical because the contractor is being paid for actual work performed.

• Cost documentation matters most in cost-plus, T&M, and GMP, because the owner's payment obligation depends on it. The contract should specify what counts as a reimbursable cost, what backup is required, and what audit rights the owner has.

• Open-book provisions and audit rights are essential in cost-plus and GMP and largely irrelevant in lump-sum.

• Liquidated damages for delay are most often seen in lump-sum contracts where the schedule is fixed and quantifiable damages can be predicted.

The clause-by-clause checklist I would give a homeowner is meaningfully different for each structure. Reading a cost-plus contract through a lump-sum lens — or vice versa — produces both false alarms and missed risks.

Statutory and procedural backdrop

Regardless of structure, every Colorado residential construction contract sits inside the same procedural framework. The Construction Defect Action Reform Act at C.R.S. § 13-20-803.5 governs the notice-and-cure procedure for defect claims. The mechanics' lien framework in Title 38 Article 22 governs the contractor's payment-security rights. The Colorado Consumer Protection Act at C.R.S. § 6-1-105 creates remedies for deceptive practices in the contract or its performance. These overlays apply whether the contract is lump-sum, cost-plus, T&M, or GMP; the structure shapes the project economics, but the procedural framework is constant.

The starting move

When a homeowner sends me a contract to review, my first question is not "what does it say." It is "what structure is this." Once that is answered, the rest of the review is far more efficient, because I know what risks the document needs to allocate and what protections the owner needs to negotiate. Knowing the family makes the words make sense.