This house combines a gothic arch with a sawtooth roof, which is less a style choice than a ventilation one. The sawtooth puts a stack of openings along the ridge, so the hot air that collects under the roof leaves at the high point rather than being pushed out sideways, and the crop sits in moving air instead of still air. The frame is hot dip galvanized steel on a multi span layout, and the covering is a tri layer film with UV stabilisation, which is what a project buyer usually specifies where the cover is replaced on a five year cycle.
A greenhouse roof has two jobs that pull against each other: let light in, and let heat out. The sawtooth profile is a way of doing both, because the ridge carries a run of openings at the highest point of the house, where the hot air has already arrived. This house pairs that roof with a gothic arch frame, so it also sheds snow rather than holding it.
On a standard ridge or round arch house the vents sit along the ridge line and air is exchanged across the width of the house. The sawtooth works differently: each tooth has a vertical face, and the openings sit in those faces at the top of the house, so the warm air leaves from the highest point rather than from the sides. The result is a house that flushes through instead of stirring, which is what keeps a dense tomato crop out of still, humid air.
That matters most where a crop is grown at high density for a long season. Still air under a closed roof is where leaf disease establishes, and the sawtooth is designed to remove the pocket the disease starts in rather than to treat it afterwards. Houses of this arrangement are grouped on the sawtooth greenhouse range page on this site.
The frame is hot dip galvanized steel. Spans run from 8 m to 12 m, lengths from 10 m to 100 m or set to the site, and the working height from 3 m to 8 m. Galvanizing is applied after the tubes are formed and drilled, so the cut ends and bolt holes are protected and the structure needs no secondary treatment once it is up.
The standard cover is a 200 micron PEP tri layer film with UV stabilisation, running at around 90 per cent light transmission and replaced on a five year cycle. A tri layer film is specified rather than a single layer because the inner layers carry the anti drip and anti fog treatment, so the additives are not exposed to the weather on the outside face. Where a rigid cover is wanted, a sheet cover can be specified on the same frame.
Side and top vents are optional and are set to the site. On a house that already has the sawtooth working, the extra vents are used for the shoulder seasons rather than for the peak, when the sawtooth alone is doing the work. A fan and pad set can be added for cooling where summer temperatures would otherwise close the house down, and drip irrigation is run on the same layout as the beds.
Because the roof openings run the length of the house, the ventilation is even along the bay rather than concentrated at the gable ends, and a project can be extended along the same line without the far end becoming the hot end.
The table below is the standard build. Span, length, height and the ventilation package are set to the site and to the crop.
| Roof type | Gothic arch with sawtooth ridge ventilation |
| Structure material | Hot dip galvanized steel |
| Span | 8 m, 9 m, 10 m, 11 m or 12 m |
| Length | 10 m to 100 m or set to the site |
| Working height | 3 m to 8 m |
| Cover | 200 micron PEP tri layer film, UV stabilised |
| Light transmission | About 90 per cent |
| Film service cycle | About 5 years |
| Ventilation | Sawtooth ridge openings; side and top vents optional |
| Cooling | Fan and pad set optional |
| Irrigation | Drip irrigation set to the bed layout |
| Crops | Tomato, vegetables, fruit and cut flowers |
| Customisation | Span, length, height and ventilation set to the site |
A multi span house is built to a setting out drawing. Ground posts or a base rail are set and levelled first, because the load comes down the gutter columns and the side lines. The bays are raised one at a time, the gutter line and the bracing follow, the sawtooth openings are framed, and the cover goes on after the frame is closed. Beds and the drip layout are set out once the house is watertight.
Upkeep follows the roof and the cover. The sawtooth openings are checked for free movement at the start of each season, since an opening that sticks turns the house back into a standard one, and the frame around them is inspected for the load a long run of openings puts on the ridge. The film is checked at the fixing points and where it crosses the frame, and replaced on the five year cycle rather than patched through it.
Houses of this type are used for commercial tomato production over a long season, for vegetable and fruit programmes where the crop is grown at density, and for cut flowers under a ventilated cover. They suit project buyers specifying a block rather than a single house, growers moving from tunnels into a multi span build, and sites that expect to add cooling or irrigation to the same structure. A house built on the same sawtooth principle around a growing system is described in the gothic sawtooth greenhouse with hydroponic system page.
Information and programmes on protected crop production are published by the Food and Agriculture Organization of the United Nations. Production and market reporting for flower and plant growers is published by FloralDaily. A sawtooth house built for tropical ventilation is described in the natural ventilation sawtooth greenhouse page.
The height at which the air leaves. On a standard house the vents are along the ridge and air crosses the width; on a sawtooth the openings sit in the vertical faces at the top, so the warm air that has risen under the roof leaves from the highest point rather than being pushed out sideways.
Because the treatments sit on the inner layers. Anti drip and anti fog additives on a single sheet are exposed to the weather on the outside face, where they degrade fastest, and a tri layer film keeps them where they do the work.
The galvanized steel frame is rated for 15 to 20 years under normal growing conditions. The film cover runs on about a five year cycle, and the vent drives and cooling gear on their own service schedules.
We provide a 10 year structural warranty and a 5 year anti-corrosion warranty on the galvanized steelwork. Details are set out in the contract for each project.
Send your site dimensions, the crop you plan to run and the growing layout you intend to use. We reply with a layout drawing and a full quotation.
