Symptoms
- Visible crack line across the glass
- Crack lengthening over time or after temperature swings
- Drafts or noise through the crack
- Sharp edges near the break
Likely causes
- CommonImpact from an object (ball, branch, rock)A direct hit is the most common cause of a single crack.
- PossibleThermal stressRapid temperature change, like cold glass hit by direct sun, can crack it without impact.
- PossiblePre-existing stress from an improperly installed frameA frame that's slightly out of square can put constant pressure on the glass until it cracks.
- Less commonAge and settlingVery old glass can crack from decades of minor building movement.
What to do
- Cover the crack immediately on both sides with clear packing tape to hold pieces in place and reduce drafts.
- Keep people and pets away from the area, especially if the crack is spreading or the glass is loose.
- For a small single-pane crack, a temporary clear silicone sealant applied to a cleaned crack can slow spreading, but this is not a permanent fix.
- Measure the glass opening (width and height) for an eventual replacement quote.
- Decide between pane-only replacement (single-pane windows) or a full insulated glass unit swap (double-pane).
- Schedule a glass company to measure and replace the pane; avoid removing large cracked pieces yourself due to injury risk.
- Once replaced, dispose of the old glass carefully, wrapped and marked, since curbside pickup rules for glass vary.
Tools and parts
- Clear packing tape
- Tape measure
Replacement window glass paneSearch: “window glass pane replacement”
When to call a pro
Call a glass company or window installer for the actual replacement, especially for large panes or upper-floor windows.
Safety
Use caution
Cracked glass has sharp edges and can shatter further; wear gloves if you touch it and keep children and pets away until it's covered or replaced.