Greenhouse and Canopy Glazing
Summary
Greenhouse and canopy glazing covers translucent roof and wall coverings of glass, multiwall polycarbonate, or ETFE film over lightweight frames. Light transmission, diffusion, weight, and service life trade against each other, and sloped overhead glazing falls under the sloped glazing rules in the parent note.
Cols
Terminology
- PAR (photosynthetically active radiation): light plants use for growth
- Diffuse glazing: covering that scatters light to reduce shadows
- Multiwall polycarbonate: extruded sheet with internal walls that insulate
- ETFE film: lightweight fluoropolymer foil, single or inflated multilayer
- Horticultural glass: low-iron glass with high light transmission
- Sloped glazing: glazing more than 15 degrees from vertical
Standards
Light transmission (vendor data)
- Horticultural glass: about 88 to 92 percent of PAR
- Multiwall polycarbonate: about 74 to 82 percent of PAR, depending on wall count; yellowing and measurable loss usually appear around years 10 to 15
- Single-layer ETFE: about 87 to 95 percent of PAR; can be made to diffuse light
- Check figures against independent test data before specifying
Related standards
- Sloped glazing follows the code provisions in the parent note, including allowable glass types and screens
- ASTM E1300: glass load resistance
- Product standards for polycarbonate and ETFE follow their maker's listings
Materials
- Glass: the heaviest covering, with high transmission and the greatest structural load
- Multiwall polycarbonate: the most common greenhouse covering
- ETFE film: lighter than glass and resistant to UV
- Laminated or heat-treated glass: canopy and overhead safety
Detailing
- Size the frame for the covering's weight and for snow, wind, and maintenance loads
- Use laminated glass or protective screens where glass is overhead
- Drain and flash the low edges and ridges to move water off the covering
- Provide ventilation and shading for solar gain in greenhouses
- Allow for thermal movement of polycarbonate and film in the frame
Uses
Specific uses
- Commercial and home greenhouses
- Conservatories and garden rooms
- Entrance and walkway canopies
- Atrium and courtyard coverings
- Covered growing spaces in public buildings
Pros and cons
Pros
- Admits daylight overhead
- Polycarbonate and ETFE are lighter than glass
- ETFE and polycarbonate can diffuse light
Cons
- Glass is heavy and can break overhead
- Polycarbonate yellows with age
- Overheating without shading and ventilation
Manufacturing and cost
Construction
- Coverings are fixed to aluminum or steel frames with gaskets and caps; film is tensioned in extruded channels, and sheet is clipped or glazed into profiles
Main manufacturers and suppliers
Sources
- Greenhouse Grower: how to select the best glazing for your greenhouse operation, https://www.greenhousegrower.com/technology/how-to-select-the-best-glazing-for-your-greenhouse-operation/
- Ceres Greenhouse Solutions: choosing the best glazing for your greenhouse, https://ceresgs.com/choosing-the-best-glazing-for-your-greenhouse/
- Ceres Greenhouse Solutions: benefits of ETFE material, https://ceresgs.com/discover-benefits-of-etfe-material/
- ADAS: ETFE film vs glass and polycarbonates, https://me.com.sg/article/ETFE-film-vs-glass-and-polycarbonates