Glass-only or a whole window?
| Problem | Usually fixable with glass only? |
|---|---|
| Single cracked or broken pane | Yes |
| Fog or haze between the panes of a double-pane unit | Usually; the sealed unit is replaced |
| Rot in the sash or sill | No; the sash or window needs work |
| Sash won't stay up, balance broken | Parts repair, not glass |
| Drafts around the frame | No; air sealing or replacement |
| Many units failing at once | Often cheaper to replace windows |
How insulated glass is replaced
A modern double-pane window holds a sealed insulated glass unit (IGU): two panes, a spacer around the edge and a seal. The installer measures the existing unit precisely, orders a new IGU to that size and thickness, removes the glazing stops and sets the new unit with fresh glazing tape or sealant. Ordering takes days to a couple of weeks, depending on the supplier.
If you are replacing several units, ask whether low-e coated glass can be specified. It costs a little more and the new panes will outperform the original clear glass. More on fogged units is on double-pane windows.
Safety glass
If the broken pane is in a door, next to a door, near a tub or shower, by a stair, or is a large low pane near a walkway, the replacement must be tempered or laminated under the 2018 IRC (R308.4). Older houses sometimes have plain glass in these spots from before the rule; a replacement is the time to correct it.
Old single-pane wood sashes
Wavy original glass in a 1900s Knoxville house is set in glazing putty. A glazier can reglaze a single broken pane and keep the rest of the original glass, which matters inside a historic overlay. Lead-safe practices apply to houses built before 1978.
Cost
National guides put glass replacement at roughly $250 to $1,000 per job, with a standard double-pane glass unit around $150 to $400 per panel. Size, tempered or low-e glass and access (second floor, large picture units) push the figure up. See window replacement cost to compare with a full window.
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