Greenhouse buyers compare price per square metre and then discover that a 4 mm twin-wall panel is not interchangeable with a 10 mm triple-wall one. The layer count sets the insulation, the span and the growth outcome.
What the layers do
- 4 mm twin-wall — U-value near 3.0 W/m²K, light transmission about 82%, practical roof span around 1.0 m.
- 6 mm twin-wall — U-value near 2.9, span to about 1.1 m.
- 8 mm triple-wall — U-value near 2.2, span to about 1.3 m.
- 10 mm triple-wall — U-value near 2.0, span to about 1.5 m.
- 16 mm five-wall — U-value near 1.5, used where night heat retention dominates.
Three climates, three answers
Cold continental. 10 mm triple-wall on the roof and 8 mm triple-wall on the walls, with the roof span held under 1.5 m. The extra layer buys nights that stay above freezing without heating.
Hot arid. 4 mm twin-wall with an opal or diffusing grade. Insulation is not the problem; direct radiation is, and an opal panel spreads light without cooking the crop.
Temperate humid. 6 mm twin-wall with an anti-drip and anti-fog coating. Condensation dripping onto leaves is how fungal pressure starts, so the additive matters more than an extra millimetre.
What a supplier must prove
UV protection has to be co-extruded on the outer face, not applied as a film, or the panel chalks within four seasons. The supplier should state the UV layer thickness in microns, the warranty period against yellowing, and the panel’s span table at a defined snow load. Without those three, a cheaper panel is a two-year greenhouse.
The solid-sheet comparison is covered in greenhouse polycarbonate sheet, and the roof glazing case in polycarbonate skylight roofing.
Frequently Asked Questions
Q: What thickness polycarbonate is best for a greenhouse?
A:It depends on climate. Cold regions do best on 10 mm triple-wall for insulation; hot climates do better on 4 mm twin-wall in a diffusing grade; humid temperate sites favour 6 mm twin-wall with anti-drip coating.
Q: How should greenhouse polycarbonate be UV protected?
A:By a co-extruded UV layer on the outer face, not a film. Ask for the layer thickness in microns and a yellowing warranty, or the panel will chalk within a few seasons.
Send your house footprint, span and climate zone to oversales@rpplexiglass.com for a polycarbonate panel schedule and container plan.