A greenhouse or roof glazing project is a long-term bet on a material that has to resist sun, hail, heat loss and a decade of weather. From years of supplying agricultural and architectural projects, I will be direct: for covered growing and rooflights, polycarbonate twin-wall is the workhorse, and glass – despite its attractive look – is often the wrong choice. Here is the engineering picture.
Thank you for reading this post, don't forget to subscribe!Polycarbonate twin-wall versus glass
When a grower or architect compares a rooflight system, the decisive numbers favour PC twin-wall:
- Weight – PC multiwall is a fraction of the weight of glass, so the supporting structure and craneage are far cheaper and the roof loads drop
- Thermal insulation – the trapped air cells give a U-value that outperforms single glass and even competes with double glazing, saving heating energy every season
- Impact and hail – PC survives hail strikes and accidental impacts that shatter glass, protecting the crop and the people underneath
- Light diffusion – the translucent structure spreads sunlight more evenly, reducing shadow and leaf burn compared with clear glass
How it is used in practice
You will meet PC multiwall in four common roles. Commercial and hobby greenhouses, where twin-wall panels form the walls and roof of the growing area. Rooflights and roof lanterns on industrial and residential buildings, where a light, insulated panel replaces fragile glazing. Canopies, walkways and covered courtyards that need daylight without the weight and risk of glass. And vertical cladding on facades, where the insulating sheet controls solar gain while letting daylight through. In each case the specification is the same: the right cell geometry and thickness for the span, with the UV-protected face oriented correctly.
What is failing in the market
The failures I inspect tend to come down to corners cut on quality. UV protection that only coats one side, so the unprotected face yellows and embrittles in a couple of seasons. Thin multiwall sold on price that sags between purlins. And installation without proper thermal expansion allowance and sealing, which produces leaks and condensation. All of these are preventable, and all of them come from buying sheet instead of buying a specification.
Our advantage and solution
We manufacture polycarbonate multiwall with co-extruded UV protection on the exposed face and a documented light transmission and insulation value, so you can specify with confidence. We supply standard greenhouse widths as well as cut-to-size panels with the flutes aligned to your frame for drainage and strength. We recommend the right cell structure and thickness for your span and climate – typically 4 to 16 mm – and provide sensible installation guidance on expansion, orientation and sealing so the roof performs as designed for years.
For growers, glazing contractors and architects, send your roof or greenhouse dimensions to oversales@rpplexiglass.com for a quotation.
Frequently Asked Questions
What thickness of polycarbonate multiwall is used for greenhouses?
Typically 4 to 16 mm, chosen by span and climate: thicker cells span wider gaps and insulate better. We recommend thickness by frame and wind/snow load.
Which side of the panel faces the sun?
The UV-protected face must face outward toward the sun. Co-extruded UV protection on the exposed face is what prevents yellowing and embrittlement.
Does PC multiwall insulate better than glass?
Yes. The trapped air cells give a U-value that outperforms single glass and competes with double glazing, saving heating energy each season.