Choose greenhouse glazing by what you can find and how big the house is: salvaged glass transmits about 90% of light and lasts indefinitely but is heavy and fragile, plastic film is the practical option for large houses, and oiled cloth transmits about 60% and is a last resort. Decide the glazing first, because its size and weight set how the frame is spaced.
Glazing is the transparent skin of a greenhouse; the choice of material sets how much light enters, how much heat leaks out and how often the skin must be replaced.
Light, Insulation And Lifespan Pull In Different Directions
No glazing wins on every count. Glass gives the most light and lasts longest but weighs the most and breaks. Film is cheap and light but wears out in the sun. Cloth works when nothing else is available. The three child articles cover each in depth: Salvaged Glass, Plastic Film & Alternatives and Oiled Cloth & Animal Membrane.
This page is about greenhouse covering. It is not about ceramic glaze; if you came looking for pottery, see Glazing in the materials section.
| Material | Light passed | Lifespan | Main drawback |
|---|---|---|---|
| Salvaged glass | about 90% | indefinite | heavy, fragile, needs careful framing |
| Plastic film | varies with film and age | 1 season (hardware poly) to 3-4 seasons (greenhouse film) | degrades in UV, tears in wind |
| Oiled cloth | about 60% | must be re-oiled annually | low light, fire risk, short life |
What You Need
- Whatever glazing you have — measure what you can salvage before you plan the frame
- A frame spaced to suit it (see Frame Materials: Wood, Bamboo, Salvage)
- Sealant — linseed-oil putty for glass, battens for film
Method: Pick The Glazing
Step 1: Count what you can get. Inventory salvageable panes and their sizes. A greenhouse built around 40 matching panes is a different design from one built around a roll of film.
Step 2: Match to scale. Use glass for a small house or a south-facing wall; use film for large houses; keep cloth in reserve.
Step 3: Mix when it helps. Glass on the south face and film elsewhere spends the scarce material where light matters most.
Step 4: Plan for replacement. Film and cloth are consumables. Keep spare material and frame the house so panels can be re-covered without rebuilding.
Common Mistakes
- Choosing for looks — pick for supply, then design the frame around it.
- Mixing odd panes without a plan — irregular gaps leak heat; frame to the smallest common size.
- Forgetting that glazing sets frame spacing — decide the glazing first.
Safety
Glass and fire
Overhead glass can fall on people if the frame fails. Cloth soaked in drying oil can heat itself and catch fire when piled; see Oiled Cloth & Animal Membrane.
What’s Next
- Learn next: Salvaged Glass — the premium option in detail
- Combine with: Climate Control — what the glazing choice does to heat