Window installation: what to know

What the job involves, what changes the price, and what to ask a pro.

What window installation is

Window installation removes old windows and fits new units into the openings, with shimming, flashing, insulation, sealing and trim so the windows open smoothly and keep out water and air. People call when windows are drafty, fogged, hard to open, or rotted at the sill, or when a room needs a larger or better-performing opening.

Signs you need it

  • Drafts you can feel near the frame, or a curtain that moves when the window is closed
  • Fogging or moisture between the panes of the glass
  • Sashes that stick, will not lock, or drop when they are opened
  • Soft, dark or cracked wood at the sill, or stains on the wall below the window
  • Frames that are warped, or a window that has pulled out of square over time

What the pro does

  • Measure each opening in three places for width and height, and check the sill, jamb and head for level and square
  • Remove the sash and frame, or cut the old unit out of the opening, then inspect the rough opening for rot and water damage
  • Set the new unit level and plumb, shimming it at the anchor points so it does not bind or rack
  • Flash the sill and head with the right tape and pan flashing, then fill the gap with low-expansion foam or the insulation the manufacturer specifies
  • Install the interior and exterior trim, seal the joints with the sealant suited to the material, and test the operation and locks

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Number of windows and their sizes, and whether any openings are enlarged or reframed
  • Window type, such as double-hung, casement, sliding or picture, and the frame material
  • Glass package, including insulating value, coatings and any tinted or laminated glass
  • Condition of the rough opening, such as rot in the sill or framing that must be repaired
  • Interior and exterior trim work, including stucco or brick cuts and patches
  • Access, including second-story openings and the lift or staging needed
  • Permit and inspection requirements for changes to the openings

What a written quote should spell out

  • Window count, size, operation type and frame material, with each opening listed by room
  • Glass package named, with the coatings, gas fill and spacer type included
  • Flashing method at the sill and head, including the pan flashing and tape used
  • Insulation or foam used in the gap, and the sealant type for the exterior joints
  • Interior and exterior trim included, and any stucco, brick or siding patch work
  • Removal and disposal of old units, and cleanup of dust and debris inside the home

Questions to ask before you hire

  • How do you flash the sill and head, and what tape and pan do you use?
  • What is the glass package, and does it include the coatings and gas fill I am paying for?
  • Will you check the rough opening for rot before the new window goes in, and how will you show me?
  • How do you shim and anchor the unit so it does not bind over time?
  • What warranty covers the frame, the glass seal and the installation workmanship?
  • Who pulls the permit, and does this change the opening size?
  • Can you show me a recent install with the same window type and trim?

Red flags

  • A quote that says the window will be installed with no flashing at the sill
  • Foam filled into the gap without a plan for the exterior sealant or the flashing
  • Windows set without shims or with a frame that is racked out of square
  • Replacement windows ordered before anyone has measured each opening on site
  • A crew that cannot name the frame material, glass package or warranty

What you can do yourself

You can safely measure openings, clean tracks, and check the weatherstripping and locks on windows you can reach from the ground, and you can add a removable interior film to a single-pane window. Removing a window, cutting into the wall and flashing the opening affect water and structure, so leave them to a pro. Call a pro for rot at the sill, a window that will not stay square, or any opening that lets in water.

Licenses and permits

Window installation is commonly done by licensed general or window contractors, and changes to the opening often need a permit and inspection. Check with your state and local licensing and building offices for what applies to your home.

Window installation questions

Can I replace only the glass in my window?

Sometimes. If the frame and sash are sound, a glass unit can often be replaced. If the frame is rotted or warped, the full window needs replacing. A pro should inspect the frame before you decide.

Why does a new window still leak air?

Most leaks come from the gap around the frame, poor flashing, or sealant that was not applied to the exterior joint. Ask the installer how the gap is insulated and sealed.

Do I need to be home during the install?

Usually you should be, at least for the first and last parts of the day, so you can approve the opening and test the operation. Ask the crew how they protect your floors and furniture.

Will the new window fit my existing opening?

Only if the opening was measured correctly and the rough opening is sound. A pro should measure the opening, check for square and level, and order the unit to suit it.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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