The covering is 8 mm twin wall polycarbonate, which does two jobs at once: it diffuses daylight so the canopy is lit evenly rather than in a band under the ridge, and it traps air in the core of the panel so the cover insulates. The frame is hot dip galvanized steel set at 4 m bay spacing, which keeps the working width clear of interior posts so machinery reaches every row. Roll up side walls and a pad and fan cooling set are part of the standard specification, so the house is run to hold roughly 15 to 28 degrees Celsius. Spans run from 8 m to 12 m and length from 10 m to 100 m.
A tomato or pepper crop under cover is judged by what reaches the lower leaves on a bright day and by what the canopy does overnight. A single skin cover handles both badly: it passes light as a band under the ridge, and its inner face drops close to the outside temperature after dark, so water forms on it and falls onto the crop. A twin wall panel changes both of those at once.
Two skins with a cellular core between them turn the panel itself into the insulating layer, so the cover slows heat loss instead of only blocking wind and rain. The inner face stays warmer, which means condensation forms less readily above the canopy, and the sheet diffuses daylight across the bay rather than concentrating it under the ridge. On a vine crop that reaches two metres, diffusion is what keeps the top of the row from scorching while the lower leaves still get useful light.
The house is built as a multi span structure with the bays tied by gutters, so the cropping area sits under one roof line. The wider panel family is listed on the polycarbonate greenhouse range page on this site.
The frame is hot dip galvanized steel, dipped after fabrication so the zinc is bonded to the steel and reaches the bore, the cut ends and the wall of every drilled hole. Bays are set at 4 m spacing, and the bay width is what allows the roof to carry its load without a line of interior posts, so a tractor or a harvesting trolley works every row instead of turning around a column. Members are bolted rather than welded on site, which keeps the coating whole at every connection.
Panels are held in glazing bars on a gasket rather than fixed directly to steel, so the sheet can move slightly as it warms and cools without cracking at the fixing point, and a damaged panel is released from its channel and replaced on its own. A house on the same covering in a simpler format is described in the polycarbonate greenhouse built from twin wall panels.
Roll up side walls give passive ventilation along both long walls, and a pad and fan cooling set removes the peak of a hot afternoon by evaporating water into the incoming air. Running the two together is what holds a band of roughly 15 to 28 degrees Celsius on a fruiting crop, which is the range the plant needs to keep setting fruit. At commercial scale the side walls and the cooling are normally put on a controller so the house responds to temperature rather than to a round of manual openings.
Where a site wants a different balance between light and insulation, the same frame takes a panel house built for flower crops, described in the insulated panel house for flower crop growing.
The table below is the standard build. Span, length, height, panel and ventilation are set to the site and to the crop.
| Greenhouse span | 8 m / 9 m / 10 m / 11 m / 12 m |
| Greenhouse length | 10 m to 100 m, or built to client demand |
| Greenhouse height | 3 m to 8 m |
| Structure material | Hot dip galvanized steel, bolted assembly |
| Bay spacing | 4 m, no interior support posts across the working width |
| Cover material | 8 mm twin wall polycarbonate panel, UV resistant |
| Ventilation | Automated roll up side walls |
| Cooling | Pad and fan set, holding roughly 15 to 28 degrees Celsius |
| Options | Thermal screens, irrigation, shading and benching |
| Crops | Tomato, pepper, cucumber, lettuce and vine crops |
Assembly starts with the base, because a panel house shows any error in the foundation along its whole length and there is no give in a rigid sheet. Base plates or ground posts are set to the drawing and to the same layout as the gutters, the frame is erected and squared bay by bay, and the glazing goes on last, each panel held in its bar on the gasket. No welding is done on site at any point. A house of this size is normally standing in two to four weeks on a prepared site.
Maintenance is lighter than on a film house because the cover is not on a replacement cycle. The routine is checking panel fixings and gaskets after the first season, washing the sheets once a year because dust cuts light transmission more than growers expect, and keeping gutters and downpipes clear. On a cooled house the pads are the item to watch, because a pad that has clogged with dust or scale stops evaporating and the cooling drops away with no obvious fault.
Houses of this type are used for tomato and pepper production, for cucumber, for lettuce and leafy crops where light quality decides the grade, and for propagation. They suit commercial growers and distributors buying for projects that need a permanent covering, clear access for machinery along every row, and a house that can be cooled through a hot season without relying on a single skin cover.
Planning figures for protected cropping and for the storage and marketing of the harvested crop are published by FAO. Production and market reporting for commercial greenhouse growers is published by Greenhouse Grower. The question that decides the specification is normally the crop the house will be running in ten years, not only at handover.
The core of a twin wall panel holds air, and that air is the insulating layer, so the cover slows heat loss instead of only blocking weather. The inner face also stays warmer, which reduces condensation above the canopy, and the sheet diffuses daylight rather than passing it as a beam under the ridge.
Bays set at 4 m spacing let the roof carry its load without a line of interior posts. That keeps the whole working width clear, so a tractor or a harvesting trolley reaches every row rather than turning around a column, which is what the spacing is chosen for on a fruiting crop.
The galvanized steel frame is rated for 15 to 20 years under normal growing conditions. Polycarbonate panels keep their light transmission for 20 years or more when they are cleaned and left undamaged.
We provide a 10 year structural warranty and a 5 year anti-corrosion warranty on the galvanized frame. Details are set out in the contract for each project.
Send your site dimensions, the crops you plan to grow and your local wind and snow loads. We reply with a layout drawing and a full quotation.
