How to Replace Window Glass

To replace window glass, you remove the broken pane or failed insulated glass unit (IGU), order a replacement cut to the same dimensions and thickness, bed it in glazing compound or clip it into the frame’s existing gasket, and seal the edges. Single-pane glass in old wooden frames is a practical DIY job; double or triple-pane IGUs almost always need a glazier or a new window.

• Single-pane glass replacement costs roughly $50 to $150 per pane for materials; professional glazing runs $100 to $300 per opening in the GTA.
• Insulated glass units (IGUs) with fogging between the panes cannot be repaired: the sealed unit must be replaced entirely.
• ENERGY STAR™ certified IGUs contain low-emissivity (Low-E) coatings and argon gas fill that single-pane glass cannot replicate.
• Tempered safety glass (marked with a small etched logo in the corner) must be replaced with tempered glass of the same specification.
• If your frame is more than 20 years old, replacing the whole window is often more cost-effective than re-glazing it.

When Should You Replace Glass vs the Whole Window?

Replace the glass only if the frame is structurally sound, the glazing seals are intact, and the opening mechanism works correctly. If the frame is rotting, the hardware is failing, or the window is single-pane, a full window replacement delivers far better value. A new ENERGY STAR™ certified double or triple-pane unit will cut your heat loss through that opening by 30 to 50% compared to the old single-pane glass, savings you’ll see on your heating bill every winter.

“We get calls about glass replacement where the real issue is a 30-year-old frame that’s lost its shape,” says a lead installation manager at TotalSeal. “Putting new glass in a warped frame is like putting new tyres on a car with a bent axle. Nine times out of ten, a new window is the right call.”

Tools and Materials You’ll Need

Tools: safety glasses, cut-resistant gloves, utility knife, putty knife or glazing knife, heat gun (for old putty), tape measure, glass cutter (for single-pane DIY cuts), suction cup lifter, cordless drill (if removing stops), caulking gun.

Materials: replacement glass (order cut to size from a local glass supplier; provide exact dimensions and glass type), glazing compound or silicone (for single-pane work), glazing points or spring clips (for single-pane wood frames), exterior caulk (for modern frames with gaskets), primer and paint to finish.

For IGU replacement, the unit is factory-made to your specified dimensions and glass spec, so you order it rather than cutting it yourself. Measure the visible glass area plus the edge coverage, and note the existing glass thickness, spacer width, and coating (your glazier or supplier can help identify these from the unit markings).

Safety Notes

Broken glass is dangerous. Before touching a cracked or broken pane, put on heavy-duty cut-resistant gloves and safety glasses. Lay a drop cloth below the window to catch fragments. Never attempt to lift large panes alone; use suction cup lifters and a second person for anything wider than 60 cm. Dispose of glass in a rigid container, not a plastic bag. Tempered glass shatters into small granular pieces on failure; if you’re working with a cracked tempered pane, score a protective film across the surface with tape before removal to contain the pieces.

Step-by-Step Instructions

Allow two to three hours for a single-pane replacement in a wooden frame. IGU replacement in a modern vinyl window can take one to two hours if the frame allows the glazing bead to be removed; otherwise, call a glazier.

Step 1: Measure the Existing Glass

Measure the glass width and height at three points each and record the smallest figure. For an IGU, measure the overall unit thickness as well. If the glass is broken, measure the rabbet (the groove the glass sits in) from inside the frame to get the daylight opening, then add the edge coverage on each side to calculate overall glass size.

Step 2: Remove the Broken Pane

For single-pane wood frames: use a heat gun to soften old glazing putty, then remove it with a putty knife. Pull out the glazing points with pliers. Lift the glass out. For vinyl frames with rubber gaskets: remove the glazing bead (the plastic strip that holds the glass in) by pressing it free from the frame corner, then slide the old IGU out carefully with suction cups.

Step 3: Clean the Rabbet or Gasket Channel

Scrape all old putty, adhesive, and sealant residue from the rabbet. On wood frames, prime the bare wood with oil-based primer before bedding new glass; bare wood absorbs moisture and causes putty to crack early. On vinyl frames, wipe the gasket channel clean with a damp cloth.

Step 4: Set the New Glass

For single-pane wood frames: apply a thin bed of glazing compound into the rabbet. Set the glass onto two setting blocks (small rubber pads) at the bottom corners, then press the glass into the compound bed. Push glazing points into the frame every 200 mm around the perimeter to hold the glass in place. Apply glazing compound around the perimeter edge, tooling it to a 45-degree bevel that sheds water.

For vinyl frames with IGUs: set rubber setting blocks in the sill of the frame, lift the new IGU into position with suction cups, press it square into the opening, and snap the glazing bead back into position around all four sides. Start at the corners and work toward the middle.

Step 5: Seal and Finish

On single-pane wood frames, allow the glazing compound to skin over (24 to 48 hours), then prime and paint. On vinyl frames, inspect the gasket bead for gaps and apply a small bead of clear silicone at any corners that show a gap. Wipe off excess silicone with a damp cloth before it cures.

Step 6: Final Check

Check that the glass is seated firmly with no rocking. On opening sashes, operate the window fully to confirm the glass doesn’t contact the frame. Clean the glass with a non-abrasive cleaner.

Common Mistakes to Avoid

Mistake	How to avoid it
Ordering glass to the outside dimensions instead of the rabbet size	Measure the daylight opening, then add the edge coverage
Skipping primer on bare wood in the rabbet	Prime before bedding; raw wood will cause early putty failure
Replacing tempered with standard float glass	Always match the original glass type; tempered is a safety requirement
Leaving the frame open too long in cold weather	Order materials in advance and work quickly once the old glass is out
Not using setting blocks	Without blocks, glass rests on the frame and can crack under thermal movement
Fitting an IGU in a frame with a failed gasket	Replace the gasket at the same time or the new unit will fail early

Cost Breakdown

Glass type	DIY material cost	Professional supply and fit (GTA)
Single-pane float glass	$30 to $100	$100 to $200 per pane
Double-pane IGU (standard)	$120 to $300	$250 to $500 per unit
Double-pane IGU with Low-E and argon	$180 to $400	$350 to $650 per unit
Triple-pane IGU	$300 to $600	$500 to $900 per unit
Tempered safety glass replacement	$80 to $200	$180 to $350 per pane

DIY vs Professional Glazing

	DIY	Professional
Risks	Incorrect glass spec, failed seal, safety risk with large or tempered units	Minimal; glazier guarantees fit and unit specification
Benefits	Cost saving on simple single-pane jobs in accessible wood frames	Correct specification ordered, proper setting blocks and gaskets, warranty on the unit

“A homeowner can replace a single pane in an old storm window or a wooden cottage casement without too much risk,” says a senior product engineer at TotalSeal. “But a modern IGU with a Low-E coating and argon fill needs to be ordered to exact tolerances. Getting that wrong means the gas fill fails within a few years and you’re fogged up again.”

Next Steps

If your frame is older or you’re not sure whether glass replacement or a full window swap makes more sense, use the cost estimator to compare options before committing.

Frequently Asked Questions

Can I replace a double-pane window glass myself?

It’s possible if you can access the glazing bead on your frame type, but IGUs must be ordered to exact tolerances from a glass fabricator. A measurement error means the unit won’t fit. For most homeowners, hiring a glazier for IGU work is faster and safer.

How do I know if my insulated glass unit has failed?

Persistent fogging or condensation between the two panes that doesn’t clear with temperature change means the argon gas has escaped and the desiccant in the spacer is saturated. The IGU must be replaced.

Is it worth replacing glass in a 30-year-old window?

Usually not. A 30-year-old frame has likely degraded seals, worn hardware, and poor thermal performance overall. A new ENERGY STAR™ certified window delivers far better energy savings and often costs only marginally more than IGU replacement alone.

What type of glass do I need for a bathroom or shower-adjacent window?

Safety glass: either tempered or laminated. Building codes in Ontario require safety glazing in any window within 600 mm of a bath or shower and in full-height sidelites beside doors.

How do I measure window glass for a replacement order?

Measure the width and height of the existing glass (or the daylight opening if the glass is missing), then confirm the thickness. For IGUs, note the total unit thickness and spacer width. Take the smallest dimension if measurements vary slightly at different points.

Can fogged glass be repaired without replacing the IGU?

Some companies offer de-fogging services that drill small holes to remove moisture, but these are a temporary fix. The insulating gas is already gone, so thermal performance remains poor. Full IGU replacement is the permanent solution.