On almost every construction or renovation project, the contractor buys the materials. Lumber, drywall, wiring, fixtures, concrete, fasteners, finishing hardware — it all flows through the contractor’s purchasing network before it ever reaches the job site. Contractors have wholesale accounts, trade pricing, and the technical knowledge to order the right products in the right quantities. You can supply specific items yourself, and homeowners sometimes do, but it comes with warranty gaps, delay risk, and often less savings than expected.
Why Contractors Handle Purchasing
Professional builders don’t shop where you do. They work through wholesale suppliers and trade-only vendors that sell at significant discounts below retail — typically 20% to 50% off manufacturer’s suggested retail price, depending on the product category and the volume the contractor moves through that supplier. High-end cabinetry and custom millwork tend to carry deeper discounts. Commodity items like fasteners and basic hardware offer thinner margins.
Trade channels also carry products retail stores don’t stock. Structural lumber graded for specific load requirements, commercial electrical panels, specialized waterproofing membranes — those come through supplier networks a homeowner can’t easily access. Contractors calculate exact material yields for the project, which prevents both expensive waste and work stoppages from shortages. When a contractor orders 10% extra flooring to account for cuts and waste on an irregular room, that’s experience talking.
The logistics matter too. Contractors coordinate delivery sequencing so foundation materials arrive before framing lumber, framing lumber before roofing, and so on down the schedule. They absorb the risk of delivery damage, incorrect shipments, and backorders. That coordination is invisible on the invoice but real.
How Your Contract Type Determines Material Billing
Who bears the risk on material costs depends on the agreement you sign.
Fixed-Price (Lump-Sum) Contracts
A fixed-price contract bundles materials, labor, and overhead into one number agreed on before work starts. If lumber prices spike 30% mid-project, that’s the contractor’s problem and your price stays the same. The tradeoff is that contractors build a cushion into fixed-price bids to protect against exactly that scenario, so you may pay a premium for the certainty. This structure works best when the scope is well-defined and unlikely to change.
Cost-Plus Contracts
Under a cost-plus agreement, you pay the actual cost of materials plus a fee to the contractor, either a fixed dollar amount or a percentage of total costs. The contractor should provide receipts and invoices for every purchase so you can verify what was spent. You benefit when prices stay low and you’re exposed when the market moves against you. Cost-plus makes sense on projects where the full scope isn’t clear at the start, like renovations where surprises hide behind walls.
Time-and-Materials Contracts
Time-and-materials contracts bill labor at an hourly rate and materials at cost plus a markup. They’re common for smaller or unpredictable jobs where scoping everything in advance isn’t practical. The same documentation standard applies: you should receive paperwork for every material purchase.
The FTC recommends getting multiple written estimates before signing any contract, and making sure the agreement includes a clear description of materials, labor costs, and completion dates. The contract should also carry the contractor’s license number and any promises made during conversations.
What the Markup Actually Covers
Contractors mark up materials, and they should. The typical range runs from about 7% to 20%, though some go higher depending on complexity and business model. Some contractors charge a flat procurement fee instead of a percentage, which can help on material-heavy projects because the fee doesn’t grow as costs rise. Either structure is legitimate as long as it’s spelled out in the contract before work begins.
That markup isn’t pure profit. It covers the time spent sourcing and ordering. It covers carrying costs when the contractor floats thousands of dollars in materials on their own credit lines weeks before receiving payment. It covers the liability of storing materials on-site or in a warehouse. It covers the overhead of running a business: office space, insurance, vehicle costs, licensing fees, administrative staff. And it compensates for the risk of damage, theft, or waste beyond estimates.
Here’s the part homeowners sometimes miss. Even with a 15% markup, contractor-purchased materials often cost less than the same items at retail. If a contractor gets 30% off retail through their supplier and marks it up 15%, you still pay less than you would at a hardware store. The markup covers a real service, and the net price frequently works in your favor.
When You Might Supply Your Own Materials
You can buy your own materials, and homeowners sometimes do — usually to get a specific product the contractor wouldn’t normally source, or in the belief they’ll save money by cutting out the markup. Understand what you take on before going this route.
When you supply materials, you assume responsibility for quantity, quality, specifications, and delivery timing. Wrong tile, an incompatible faucet, materials that arrive two weeks late — those become your problems, and they can be expensive ones. Contractors typically exclude owner-furnished materials from their workmanship warranty. If a homeowner-supplied fixture fails or arrives damaged, the contractor is within their rights to charge additional labor for the time spent dealing with it.
Delay risk deserves special attention. When owner-supplied materials arrive late, the crew may have to stand down or reshuffle the schedule. Most contracts treat this as a compensable delay, meaning you could owe the contractor for idle time or the cost of rescheduling other trades. On a project with tight sequencing, where electricians need to work after framing and before drywall, a two-day material delay can cascade into a week or more of lost time.
The math on owner-furnished materials often doesn’t pencil out the way homeowners expect. You lose the trade discount, you pay retail sales tax, you spend your own time researching and ordering, and you accept the warranty and delay risk. Where it does make sense is for specialty or aesthetic items — a specific imported tile, a vintage light fixture, a custom countertop — where the contractor simply can’t source what you want through their normal channels.
Warranty Responsibility Flows Through the Buyer
When the contractor purchases materials, they’re the buyer of record, and warranty responsibility follows. If a water heater fails, flooring warps, or a window seal breaks within the warranty period, the contractor handles the manufacturer claim and coordinates the replacement. You deal with one person, not a corporate warranty department.
This has legal teeth beyond the manufacturer’s warranty card. Under the Uniform Commercial Code, adopted in some form by every state, goods sold by a merchant carry an implied warranty of merchantability. The materials must be fit for their ordinary purpose. A roofing membrane that leaks under normal weather conditions, or subflooring that delaminates within months, fails this standard regardless of what the manufacturer’s written warranty says. The implied warranty exists unless the contract specifically excludes it.
When a defective product is discovered shortly after installation, the contractor is generally expected to remove and replace it at no additional charge, then pursue reimbursement from the manufacturer or supplier. That liability chain is one of the genuine advantages of letting the contractor handle procurement. Supply the material yourself and the chain breaks — the warranty claim is now your problem, and any labor to remove and reinstall is billable.
The Lien Risk Most Homeowners Miss
This is the risk homeowners rarely think about until it’s too late. A mechanic’s lien is a legal claim that a contractor, subcontractor, or material supplier can file against your property when they haven’t been paid for work or materials. Here’s the dangerous part. A supplier can file a lien on your home even if you paid your general contractor in full, as long as the contractor failed to pay that supplier.
The scenario plays out more often than you’d think. You pay the contractor $80,000 for a kitchen renovation. The contractor buys $30,000 in cabinets and countertops from a supplier but pockets the money instead of paying the bill. The supplier files a mechanic’s lien on your home. You now owe money you thought you’d already paid, and the lien clouds your title, meaning you can’t sell or refinance until it’s resolved.
Lien waivers are the primary defense. A lien waiver is a document in which a contractor, subcontractor, or supplier confirms they’ve been paid and waives their right to file a lien for that payment. Collect lien waivers with every progress payment, not just at the end of the project.
There are four types, and the distinctions matter:
- A conditional partial waiver waives lien rights for a specific payment amount, but only once the check actually clears. This is the safest type to request with each progress payment.
- An unconditional partial waiver waives lien rights immediately upon signing, regardless of whether payment has been received. Use these only after you’ve confirmed the payment landed.
- A conditional final waiver waives all remaining lien rights upon receipt of the final payment.
- An unconditional final waiver waives all lien rights immediately. Only sign or accept this after the final payment has been received and verified.
Request waivers not just from your general contractor but from every subcontractor and major supplier involved in the project. If a subcontractor is reluctant to provide a supplier’s waiver, treat that as an early warning that a payment dispute is brewing.
Material Substitutions Require Written Change Orders
Specified materials sometimes become unavailable, backordered, or dramatically more expensive mid-project. When that happens, the contractor should propose a substitution through a formal change order: a written document describing the new material, explaining why the original is being replaced, and detailing any cost difference.
The change order should go to the project architect or designer for review before reaching you. The professional evaluates whether the substitute meets the same performance specifications as the original. If it’s a lesser product, the architect can request a credit to your contract price. If it’s a superior product, you’re generally not obligated to pay more, because the contractor chose to substitute.
Never let a contractor swap materials without going through this process. If a substitution happens without your written approval, you can require the contractor to remove the unapproved material and install what was originally specified, at no additional cost. Get every substitution documented in writing before the new material goes in. Verbal agreements about material changes are where disputes are born.
The FTC advises making sure your contract captures any promises made during conversations, including discussions about specific materials. If particular brands, grades, or product lines came up during bidding, those details should appear in the written agreement.