What payment schedule feels fair for window replacement?

The 10% retainage makes sense, but I’d make every payment depend on objectively verifiable deliverables rather than simply reaching a calendar date. For example, “delivered” should mean the correct units are on site, inspected for visible damage, and documented with photos and the order list.

The contract should also say that a damaged, missing, or incorrect window doesn’t trigger that portion of the milestone payment until it’s corrected. At the same time, an isolated disputed item shouldn’t justify withholding payment for unrelated, properly completed work. A practical clause could divide the invoice by window or work area, so undisputed installations remain payable while the affected amount stays pending.

That approach gives the contractor cash flow for completed work without treating delivery of unusable materials as progress. It also avoids turning the final 10% into the only leverage for unresolved defects.

Your point about tying each payment to a specific window or work area also raises a change-order issue. Could the contract require a written change order, signed before extra work starts, that states both the added cost and any schedule impact?

Otherwise, a contractor could describe unexpected trim repair, reframing, or a product substitution informally and then treat the milestone amounts as automatically adjusted. I’d also specify that approved changes don’t eliminate the original inspection, cleanup, punch-list, or warranty requirements.

Require a conditional lien waiver with each progress payment, followed by an unconditional waiver for that payment after the funds clear. The final payment should likewise be tied to an unconditional final waiver once the account is fully paid. This matters even after installation because an unpaid supplier or subcontractor may still be able to assert a lien, depending on local law and notice requirements.

The contract should identify which parties must provide waivers, including material suppliers where applicable, and make the contractor responsible for resolving unpaid claims. Each release should identify the specific payment period and amount, not be a blanket waiver signed before payment. For the delivery milestone, keep the waiver conditional until payment clears, and hold back the affected amount if there is a supplier claim or missing documentation. Lien-waiver rules are statutory in many places, so the contract should follow the requirements where the project is located.