What to know
- Site measuring, not sales measuring, should determine the ordered sizes.
- Air sealing and water management around the opening matter as much as the window itself.
- Insert and full-frame installations have different preparation and finishing steps.
- Inspect operation, seals, flashing and finishing with the crew before final payment.
Before installation day
A reliable project starts with a technical site measure after the contract is signed. The measurer records each opening, checks whether the existing frame is square, sound and dry, and confirms the agreed installation method for every window. Ask for the measurement sheet, since it defines what will arrive on the truck weeks later.
Confirm the schedule, how many openings will be opened at once, weather contingencies, permit requirements if any, and who is responsible for alarm sensors, blinds, window coverings and interior finishing.
- Clear a work path and three to four feet of space inside each opening
- Remove blinds, curtains, valances and fragile items near the windows
- Plan for pets, children and dust control, especially in older homes
- Ask about lead-safe or asbestos precautions in homes built before 1980
Removal and opening preparation
The crew removes the old sash and, for full-frame work, the entire frame, interior casing and exterior trim. This is the moment hidden problems appear: rotted sills, missing insulation, damaged sheathing or evidence of past water entry. Ask to see and photograph every opened rough opening before the new unit goes in.
Natural Resources Canada notes that replacing windows and exterior doors is also an opportunity to correct air leakage and insulation gaps around the opening. Any repair discovered here should be documented as a written change order before extra work proceeds.
Setting the window
The new unit is dry-fitted, shimmed level, plumb and square, then fastened according to the manufacturer's instructions. Shimming matters: a window forced into an out-of-square opening will bind, seal poorly and may void the warranty.
On a full-frame installation, the installer should establish water management first: sill protection and flashing that direct any water that gets past the exterior out and away from the wall, lapped so upper layers shed over lower ones.
Air sealing, insulation and flashing
The gap between the window frame and the rough opening is insulated and air sealed—commonly with low-expansion foam suited to windows, backer rod and sealant, or a combination. Overfilling with high-expansion foam can bow the frame and cause operating problems, so this step needs care rather than speed.
Outside, the perimeter is capped or trimmed and sealed with a compatible exterior sealant, leaving any required drainage path open. Sealing a window airtight on the inside and leaving the exterior open to bulk water is a common cause of later complaints.
Finishing and cleanup
Interior finishing may include new casing, extension jambs, or drywall return repair, depending on the contract. Confirm in writing whether painting, staining and drywall patching are included—these are frequent sources of dispute after full-frame work.
The crew should remove all old units, packaging and debris, and provide labels, model documentation and warranty paperwork before leaving.
Your walkthrough checklist
Walk every opening with the lead installer while the crew is still on site.
- Each sash opens, closes, locks and seals without binding
- Screens fit, and hardware operates smoothly on every unit
- Exterior capping and sealant are continuous, neat and unbroken
- No gaps at interior trim; no daylight visible around the frame
- Glass is undamaged and free of scratches, with labels retained
- Debris removed, and any deficiencies listed in writing with dates
Sources and further reading
This article provides general information, not building, health, financial or rebate advice. Verify requirements for your home, jurisdiction and program before proceeding.