Window installation moves quickly — an experienced crew can install multiple windows in a day. That speed means the window of opportunity to ask questions and verify the work is being done correctly is short. Here’s what to look for, what to ask, and when.

“The most important moment during a window installation is right after the old window is out and before the new one goes in. That’s when the rough opening is exposed, when any past water damage or rot is visible, and when the flashing has to be done correctly. Ask to see it. Take a photo of it. That moment is worth more than everything that happens before and after.”

— Theresa Huang, certified window and door installer and building envelope consultant with 16 years of experience in residential fenestration in the local area

Before Work Starts

Back view of unrecognizable craftsman using cordless screwdriver and assembling window while screwing metal hinge during renovation works in apartment

Can you confirm the installation sequence for today?

Ask the lead installer how they plan to proceed — will windows be removed and replaced one at a time, or will all windows be removed before any new ones are installed? The answer matters: leaving multiple openings in the building envelope simultaneously is a risk in cold or wet weather.

A quality installation removes and replaces one window at a time.

How will my interior finishes be protected?

Window installation involves cutting, prying, and handling heavy units near finished walls, floors, and trim. Ask how interior surfaces will be protected — drop cloths on floors, protection on windowsills and adjacent trim, and how the crew will manage any lead paint precautions if your home was built before 1978.

At the Critical Moments

a room that has a bunch of tools in it

Can I see the rough opening before the new window is installed?

For a full-frame replacement, ask the installer to call you when the old window is out and before the new one is set. This is your only chance to see the rough opening — its condition, the state of the framing, whether flashing was present before and how it performed, and whether any rot or moisture damage is present.

Take your own photos. This documentation matters if issues surface later.

Is there any rot, damage, or past water infiltration in the rough opening?

Ask the installer directly: what does the rough opening look like? Is the framing dry and solid? Were there signs of past water infiltration? If damage is found, what’s the plan before the new window is installed?

Any rot or damaged framing should be repaired before the new window goes in — not shimmed around or covered up.

Can I see the flashing tape being applied on the first window?

Ask to watch the flashing tape installation on at least the first window. A proper installation will show:

  • Sill pan flashing at the bottom, sloped to drain
  • Flashing tape at the jambs (sides), lapping over the house wrap
  • Flashing tape at the head (top), lapping over the jamb tape

If any of these steps are being skipped, raise it immediately — before that window’s exterior trim goes on.

During Installation

Is the window being shimmed and levelled correctly?

Ask the installer to confirm the window is plumb (vertical), level (horizontal), and square before it’s fastened. A window that’s installed out of square won’t operate correctly and may allow air and water infiltration at the corners.

How is the interior gap being sealed?

The gap between the window frame and the rough framing should be filled with low-expansion spray foam or fibreglass batt, then sealed on the interior with vapor barrier tape or caulk before interior trim is installed. Ask to see this step before interior trim covers the gap.

Are any windows arriving damaged?

Before each window is installed, ask whether the installer inspected it for chips, cracks, or seal failures. Damage that’s installed and then covered by trim becomes your problem to warranty later.

After Each Window

Can you show me the exterior before the trim goes on?

After each window is installed and flashed but before exterior trim is applied, ask for a quick look at the exterior perimeter. Confirm the flashing tape is in place, the window is sitting flush, and the exterior interface looks clean.

Is the hardware operating correctly?

Test each window before the crew moves to the next one: open and close it, engage the lock, check the tilt-in function if applicable. Hardware problems are much easier to address on the day of installation than after the crew has left.

At the End of the Day

Has the site been cleaned up?

Old windows, packaging material, and debris should be removed daily. Broken glass from old units is a safety hazard. Ask the crew to confirm the site is clean before they leave.

Are there any issues I should know about?

Before the crew leaves, ask directly: were there any surprises, any conditions that were different from what was expected, or anything I should be watching for in the next few weeks? This gives the installer an opportunity to flag anything that came up without you having to dig for it.

After the Job: Your Own Inspection

A few days after installation — and certainly after the first rain — do your own inspection:

  • From inside: Look for any daylight at the frame perimeter. Feel for drafts on a windy day. Check for any condensation between the panes (a sign of a damaged seal).
  • From outside: Look at the caulking perimeter — is it continuous and properly tooled? Is there any gap between the exterior trim and the siding?
  • After rain: Check the interior sills and corners for any signs of moisture infiltration.

Report any issues to the contractor in writing promptly.

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