The sawtooth roof is a ventilation decision before it is a shape decision. Instead of a ridge line with vents along it, the roof carries a run of vertical faces at the high point, so the hot air that has risen under the cover leaves from the top of the house rather than being pushed out sideways. In a hot climate that is the difference between a crop that keeps setting fruit and one that stalls at midday, and it does the work without fans.
In a hot climate the limiting factor is not temperature on its own, it is temperature combined with humidity. A house that heats up under a closed cover holds the air the crop is transpiring, and a tomato crop in still, humid air stops setting and starts losing leaf. The roof is where that is solved or not.
A sawtooth roof puts the openings in vertical faces at the top of the house. Air leaves from the highest point rather than being pushed out across the width, which means the house flushes through instead of stirring, and the volume of warm air that has collected under the cover is removed rather than diluted.
Because the openings run the length of the house, the ventilation is even along the bay rather than concentrated at the gables. On a long block that is what stops one end being the cool end and the other being the hot end, and it is why a sawtooth block can be extended along the same line without the far end becoming a problem. Houses of this arrangement are grouped on the sawtooth greenhouse range on this site.
The house combines top and side openings, which is what a tropical or monsoon climate needs. Topventilation removes the buoyant warm air, and side ventilation brings in cooler air at crop height, sothe two together give a through draught rather than a single opening doing both jobs badly.
Doing it without fans is the commercial point. Powered cooling costs money every hour it runs andstops working when the supply does, while a sawtooth roof is passive and costs nothing after it isbuilt. On a site where the summer runs long, that is the difference between a crop that can be growneconomically and one that cannot.
The structure is rated for a wind load of 0.6 kN per square metre and a snow load of 0.5 kN persquare metre, and the roof drainage is rated for 140 mm of rain per hour. Those are the figures aproject buyer needs, because they are what decides whether a house is suitable for a site at all, andthey are quoted rather than left to the buyer to assume.
The frame is a galvanized steel structure on a gothic-inspired profile, which carries the sawtoothopenings at the crown while still shedding rain off the roof faces. Span and height are fullycustomizable, so the same design is used for a small block and for a large one with the frame spacingset to the load case rather than the design changed.
The table below is the standard build. Span, height, ventilation and frame spacing are set to the site and to the crop.
| Roof type | Sawtooth with vertical ventilation faces |
| Structure material | Hot dip galvanized steel |
| Ventilation | Top and side openings, passive |
| Wind load | 0.6 kN/m2 |
| Snow load | 0.5 kN/m2 |
| Rain capacity | 140 mm/h roof drainage |
| Span and height | Fully customizable |
| Growing system | Suits a hydroponic layout under the cover |
| Crops | Tomato, vegetables, fruit and flowers |
| Other uses | Aquaculture, exhibition and research buildings |
| Customisation | Span, height, ventilation and frame spacing set to the site |
The setting out drawing comes first, with the gutter fall confirmed before any frame is raised,because the roof rain capacity is only met if the gutters carry the flow. Ground posts or a base railare set and levelled, the bays are raised one at a time, the gutter line and bracing follow, thesawtooth openings are framed, and the cover goes on after the frame is closed.
Maintenance is the openings, the cover and the gutter. The sawtooth vents are checked for freemovement at the start of each season, since an opening that sticks turns the house back into a standardone, and the frame around them is inspected for the load a long run of openings puts on the ridge. Thegutters are cleared before the wet season and the cover is checked at the fixings.
Houses of this type are used for tomato and vegetable production in hot and humid climates, forhydroponic growing under cover, and for specialised buildings such as aquaculture halls, exhibitionspace and research houses where a controlled environment with low running cost is wanted. They suitgrowers on a tropical or monsoon pattern, projects extending a sawtooth block along the same gutterline, and buyers who need the wind and snow rating quoted rather than assumed. A gothic sawtooth housebuilt for a tomato project is described in the gothic sawtooth greenhouse for commercial tomato farms page.
Research and extension material on controlled environment horticulture is published by Cornell University. Global fresh produce and market reporting is published by FreshPlaza. A sawtooth house built for tropical ventilation is described in the natural ventilation sawtooth greenhouse page.
By putting the openings in vertical faces at the high point of the house. The warm air that hascollected under the cover leaves from the top rather than being pushed out sideways, and the sideopenings replace it with cooler air at crop height.
A wind load of 0.6 kN per square metre, a snow load of 0.5 kN per square metre and roof drainagefor 140 mm of rain per hour. Those figures are what decide whether the house suits a site, so they arequoted rather than left to be assumed.
The galvanized steel frame is rated for 15 to 20 years under normal growing conditions. The coverand the vent mechanism run on their own service cycles and are replaced as they come due.
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 your local wind and snow data. We reply with a layout drawing and a full quotation.
