This house is a multi span film greenhouse arranged around ventilation, with a raised ridge section that opens along the length of the roof. Warm air leaves at the ridge and fresh air enters at crop level, so the house can be worked through spring and autumn instead of being closed up between the seasons. The frame is hot dip galvanized steel, bolted rather than welded on site, and the cover is a three layer compressed PE film. Spans run from 8 m to 12 m and length from 10 m to 100 m. The build is set to the site and to the crop.
Most film houses in a temperate climate are built for one problem and then used for another. A house sized for winter holds its heat well and then cooks the crop in early summer, because the only opening is too high and too small to clear the air that collects over the plants. This one starts from the other end: the roof is shaped so that the warmest air leaves continuously, which is what makes the same house work from the first sowing through to the last harvest.
A section of the roof is lifted above the line of the house and opens along its full length. Because warm air inside is lighter than the air outside, it rises and leaves through that opening without a fan, and because the opening runs continuously rather than at intervals, the exhaust is spread over the whole building instead of concentrated at one point.
That matters most in the middle of the day, when the layer of air just under the roof is at its warmest and the crop is at its most active. A house with the vent only at one point has to be opened wide to clear the same volume of air, which lets rain in with the air and swings the temperature through the cycle. A running vent moves the same air at a smaller opening. Houses of this family are grouped on the sawtooth greenhouse range page on this site.
Cold mornings and warm afternoons pull in opposite directions, and a house that only closes or open fully spends the season swinging between too little air and too much. The ridge vent and the side openings are worked as two stages instead. In the morning the ridge alone clears the air that built up overnight; as the day warms the sides come in as well, and they are the first thing closed again when the sun goes off the house.
That is also why this house suits vegetable production rather than only winter forcing. Leafy crops and seedlings that fail on a wet canopy do better in a house that can be vented between showers, and a house that can be worked in autumn extends the season at the end of the year as well as at the start. A house built around the same problem in a hot climate is described in the naturally ventilated sawtooth house for tropical growing.
The frame is hot dip galvanized steel, galvanized after the sections are formed, so the zinc reaches the bore of the tubes, the cut ends and the inside of every drilled hole. Columns and trusses are bolted rather than welded on site, which leaves the coating intact and lets a damaged member be unbolted and replaced instead of cut out. Spans run from 8 m to 12 m and the length is set anywhere from 10 m to 100 m.
The cover is a three layer compressed PE film. The layers carry their additives separately, so the anti condensation face keeps working for longer than a single layer sheet does, and the outer layer carries the UV stabiliser. Film is held on the hoops and the base rail with clips, which means a panel can be released and retensioned without a full recover. A single span house in the same ventilated family is described in the sawtooth single span house with side ventilation.
The table below is the standard build. Span, length, height and cover 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, or custom |
| Structure material | Hot dip galvanized steel pipe, bolted assembly |
| Cover material | Three layer compressed PE film |
| Ventilation | Raised ridge vent section along the roof plus side openings |
| Roof type | Multi span, arch roof with a raised ridge vent section |
| Cooling | Fan and pad cooling system optional |
| Crops | Leafy vegetables, seedlings, tomato and other fruiting crops |
| Customisation | Span, length, height and cover set to the site and the crop |
The kit arrives formed and drilled with the fittings, so the work on site is bolting and tensioning rather than fabrication, and no welding is done at any point. Ground posts or a base rail are set to the drawing first, the arches and the raised ridge section go up together because the vent is part of the frame geometry rather than an addition, and the film is pulled over last.
Maintenance is mostly about the openings and the film. The ridge vent, the side openings and their gear are the working parts, so they are checked and greased before the season turns. Film tension is checked after the first season and the cover renewed on a planned cycle, while the frame runs for far longer than the film does.
Houses of this type are used for leafy vegetables and seedlings, for tomato and other fruiting crops, and for nurseries that work through both ends of the year. They suit growers in temperate and transitional climates who need the house closed down on a cold morning and opened out again the same afternoon, and operations that expect to add cooling, irrigation or a control system to the same frame later.
Research and extension material on protected crop production, including work on the growing environment under cover and on ventilation, is published by NC State University through its horticultural science department. Production and market reporting for growers working under cover is published by FloralDaily. The specification that matters is the one that still suits the crop ten years from now.
Yes. Warm air inside the house is lighter than the air outside, so it rises and leaves through the opening above the ridge while cooler air is drawn in at the sides. That keeps the house venting through a power failure, which a fan system will not do.
It is the first stage rather than the whole answer. The ridge clears the air under the roof, and the side openings bring the intake down to crop height. Where a site needs more than the two can give, a fan and pad set is added to the same frame and the vents then run as the stage below it.
The galvanized steel frame is rated for 15 to 20 years under normal growing conditions. The film cover runs on a shorter cycle than the frame, typically 3 to 5 years depending on UV exposure at the site.
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, snow and rain figures. We reply with a layout drawing and a full quotation.
