Salvaged glass is the premium greenhouse glazing: it transmits about 90% of light, insulates better than plastic and lasts indefinitely, but it is heavy, fragile and needs a frame built around the panes. Seal each pane into its frame with linseed-oil-and-chalk putty, or with silicone if you can salvage it.
Part of Glazing Options
Salvaged glass is window and door glass recovered from ruined buildings and reused as greenhouse covering.
Glass Costs Effort Up Front And Nothing Afterward
A pane of glass does not wear out in the sun, does not tear in wind and does not need re-covering every few seasons. Its price is paid at the start: finding enough panes, getting them home unbroken and building a frame that holds them. If you can pay that price, glass is the best covering for a small house or a south-facing wall. Glass Recovery explains lifting panes out whole; Flat Glass covers how window glass is made.
What You Need
- Panes — measure them all before building; sort them by size
- A frame spaced to the panes (see Frame Materials: Wood, Bamboo, Salvage)
- Putty — linseed oil mixed with chalk powder, or silicone if you can salvage it. Lime Putty is a different material and not a glazing putty
- Gloves, eye protection and a way to carry glass on edge
Method: Fit The Panes
Step 1: Sort and measure. Group panes by size. Design the frame around the most common size.
Step 2: Check for tempered glass. Tempered glass cannot be cut and crumbles into pieces when it breaks; keep it for whole-pane uses. Laminated glass holds together when broken, which makes it safer overhead.
Step 3: Build the frame to the panes. Leave a small gap around each pane for the putty bed and for movement.
Step 4: Bed and seal. Press putty into the rebate, set the pane, and run a bead around the outside. Seal the joints so rain cannot run behind the glass.
Step 5: Overlap on a slope. On a sloping roof, lap each pane over the one below like roof tiles so water runs off the surface instead of into the joint.
Worked Example
Weight of a roof of salvaged panes. A 3 mm pane weighs 0.003 m × 2,500 kg/m³ = 7.5 kg/m² (using 2,500 kg/m³ as a standard figure for soda-lime glass, recalled rather than looked up). A 3 m × 4 m roof is 12 m², so its glass weighs 7.5 × 12 = 90 kg, which acts as a force of 90 × 9.81 = 883 N before the frame is counted. Thicker panes weigh in proportion: a 4 mm pane is 10 kg/m².
Common Mistakes
- Building first, finding glass later — odd sizes mean odd frames and gaps that leak heat.
- Cutting tempered glass — it shatters; test a corner or check for the etched mark before you try to score it.
- Old putty with asbestos — see the warning below.
Safety
Broken glass and old putty
Glass edges cut deeply. Wear gloves and eye protection when cutting or clearing glass, and carry panes on edge. Old window putty may contain asbestos: do not sand, scrape dry or burn it, and keep it damp when removing it; see Glass Recovery. Overhead glass can fall if the frame fails, so keep people out from under a new roof until it has stood through its first strong wind.
What’s Next
- Learn next: Plastic Film & Alternatives — what to use when glass runs short
- Combine with: Frame Materials: Wood, Bamboo, Salvage — the frame that carries it