TL;DR
Cutting glass to size requires one firm scoring pass with a glass cutter along a straight edge, then snapping cleanly along the score. Replacing a broken pane in a wood frame takes 30 minutes: remove broken glass and old glazing, set new glass in a bed of fresh compound, hold with glazier's points, and apply finish compound. Emergency temporary repairs with plastic sheeting keep a space weathertight within minutes.
Glass edges are extremely sharp and glass fragments are dangerously fine. Wear thick leather gloves at every step when handling glass — cutting, installing, and especially removing broken panes. When removing broken glass from a frame, work from the interior if possible and have a second person hold the exterior. Never work below a broken window without eye protection.
Emergency Temporary Repair
Before attempting glass work, get the opening weather-sealed. A broken window in winter loses heat equivalent to leaving your front door open.
Plastic sheeting installation:
Plastic sheeting repair is not a substitute for glass — it degrades rapidly in UV, punctures easily, and offers minimal security. Replace with permanent glazing within 30-60 days.
Understanding Window Construction
Most residential windows fall into two categories:
Single-pane wood frames: The most repairable. Glass sits in a rabbet (a groove cut in the frame), held in place with small metal clips (glazier's points) and sealed with glazing compound. You can remove the glass, replace it, and reglaze with basic tools.
Double-pane insulated glass units (IGU): Factory-sealed glass sandwiches. When the outer seal fails, the unit fogs — and cannot be repaired. Replacement requires a new factory-made unit matched to the frame dimensions. Emergency substitution with single-pane glass is feasible for a temporary fix.
Aluminum frames: Glass is held by a snap-in vinyl bead on two sides and butyl tape on the others. The snap bead pries off and snaps back after glass replacement. Slightly more involved than wood frame work but accessible with basic tools.
Cutting Glass to Size
Single-pane glass is the most common material for window replacement and comes in standard thicknesses: 3/32-inch (DS, double-strength) for most residential windows, 1/8-inch (SSB, single strength) for small lights, and 3/16-inch or 1/4-inch for larger panes.
Tools needed:
- Glass cutter (carbide wheel or diamond tip)
- Straightedge (a level, a metal ruler, or a piece of angle iron)
- Light machine oil (or kerosene, or window cleaner) to lubricate the score
- Running pliers or a smooth rounded dowel for snapping
- Leather gloves
Measuring: Measure the opening frame size, then subtract 1/8 inch from each dimension. This 1/8-inch clearance on all sides allows for thermal expansion and frame imperfections.
Scoring:
Snapping:
Grinding sharp edges: The cut edge of glass is razor-sharp. For any glass you will be handling repeatedly, run a wet diamond hand paddle or a whetstone along the cut edge at a 45-degree angle to remove the sharpest edge.
Replacing Glass in a Wood Frame
Sourcing Glass Without Hardware Stores
Salvage sources: Old windows from demolition sites are the most consistent source of single-pane glass. Furniture glass (mirrors, cabinet doors, tabletops) can be cut to size.
Acrylic or polycarbonate: Clear acrylic (Plexiglas) and polycarbonate both transmit 90% of visible light. They cut with a circular saw (fine-tooth plywood blade), a jigsaw, or by scoring-and-snapping the acrylic. Polycarbonate is impact-resistant (it does not shatter) — significantly safer in windows that may experience repeated impacts. Both materials expand and contract more than glass — allow 1/8-inch clearance per foot of dimension.
Oil-paper panes: Waxed paper or oiled silk (linseed oil-soaked cloth stretched on a frame) transmits diffuse light and blocks wind. Traditional in Japan (shoji screens) and used in European buildings before glass became affordable. Not transparent, but significantly better than solid infill for light transmission.
Sources
- Stanley Tools - Glass Cutting Guide
- This Old House Window Repair Tutorials
Frequently Asked Questions
How do you cut glass without a glass cutter?
A sharp tungsten carbide drill bit or a carbide scoring tool can score glass in a pinch. Diamond-tipped scribes used for metalworking also score glass. The scoring process is identical — a single firm pass with consistent pressure along a straight edge. Snapping along the score line is the same regardless of tool. A glass cutter costs under $5 and is worth having in any repair kit.
What is glazing compound and can you substitute anything for it?
Glazing compound (glazier's putty) is the flexible sealant that holds glass in a wood frame and seals the gap between glass and frame. It must remain flexible to accommodate thermal movement. DAP 33 is the most common product. In an emergency, a mixture of equal parts linseed oil and whiting (chalk powder) makes traditional glazier's putty. Oil-based caulk is an acceptable substitute for non-period applications.
Is it safe to handle broken glass without gloves?
No. Even small glass fragments cause serious lacerations. Always wear thick leather gloves when handling broken glass, cutting glass, or removing glazed panes. Dispose of glass fragments by wrapping in newspaper before placing in a waste container.
What are temporary window repair options when glass is unavailable?
In order of effectiveness: clear polycarbonate or acrylic sheet (rigid, light-transmitting, cuts with a circular saw or jigsaw with fine tooth blade), multiple layers of 6-mil clear plastic sheeting stretched tight and stapled, plywood (blocks light but good insulation), or heavy-duty cardboard taped in place as a short-term measure. Any temporary repair should be sealed around all edges to prevent air infiltration.