In a hot humid climate the house has to move air rather than hold it. The gothic profile does that by giving the warm moist air a steep path to the top of the house, where it leaves, and the side openings replace it with cooler air at crop height. The frame is galvanized after fabrication so the coating survives a house that runs damp for most of the year, and the cover is a three layer film with the anti drip treatment on the inner face where the condensation forms.
Tropical growing is a ventilation problem before it is a temperature problem. The air inside acovered house is warm and carries the water the crop is transpiring, and once it stops moving thecanopy stays wet, the leaf stops working and disease gets its opening. The roof is where that is eithersolved or designed in.
The gothic profile gives the air a steep route to the top of the house. Warm moist air rises alongthe pitch and leaves through the openings at the crown, and as it goes it draws cooler air in at cropheight through the side openings. That is a stack effect rather than a fan: the house flushes itselfbecause of the shape and the temperature difference, with nothing to run and nothing to fail.
Because the openings run the length of the house, the exchange is even along the bay rather thanconcentrated at the gable ends. On a long block that is what keeps one end from being the wet end, andit is what makes a multi span block work in a climate where the humidity is the limiting factor.Houses of this arrangement are grouped on the multi span greenhouse range page on this site.
The steel is cut and punched first and hot dip galvanized after, so the coating covers the cut endsand the bolt holes rather than stopping at them. Every joint is bolted and there are no welds, which ona house that runs humid for most of the year is the detail that decides how long the frame lasts: aweld burns the zinc back at exactly the point where moisture collects.
The structure is prefabricated and standardised, so it ships as flat packs and goes up with handtools rather than with fabrication equipment. On a site where the local crew has not built agreenhouse before, that is what makes the difference between a house that is assembled to the drawingand one that is improvised.
The cover is a three layer extruded film with a dustproof outer face, an anti drip inner face and UVblock treatment. The anti drip layer is the one that matters in a humid climate, because it makes thecondensate run down the film and into the gutter instead of dropping onto the canopy, which is where awet leaf turns into a disease problem.
The gutters are large enough to take a tropical downpour. That is a different requirement from theone a temperate house is designed against: the rain arrives in a shorter, heavier burst, and a guttersized on an annual average will overflow into the house at the point where the water arrives.
The table below is the standard build. Span, length, ventilation openings and the gutter section are set to the site.
| House type | Gothic multi span greenhouse with film cover |
| Structure material | Hot dip galvanized steel, galvanized after cutting and punching |
| Connections | Bolted throughout, no welding |
| Ventilation | Ridge openings with side openings, passive stack effect |
| Cover | Three layer extruded film |
| Outer face | Dustproof with UV block |
| Inner face | Anti drip, condensate runs to the gutter |
| Rain | Large gutters sized for tropical downpours |
| Delivery | Prefabricated flat packs, assembled with hand tools |
| Crops | Vegetables, fruit and flowers |
| Customisation | Span, length, openings and gutter section set to the site |
The setting out drawing comes first, with the gutter fall confirmed before any frame is raised,because the rain arrives in a burst and a gutter that is flat or back-falling will overflow. Groundposts or a base rail are set and levelled, the bays are raised one at a time, the gutter line andbracing follow, the end walls are framed, and the film is fitted once the frame is closed.
Maintenance is the cover, the openings and the gutter. The film is checked at the fixings and alongthe eave where it takes the wind, and the vent openings are cleared and tested at the start of the wetseason, because an opening that sticks turns the house back into a sealed one. The gutters are clearedbefore the rains rather than during them, and the bolted joints are gone over at the same time.
Houses of this type are used for vegetable and fruit production in tropical and monsoon climates,for cut flowers on a hot humid site, and for any block where the humidity rather than the temperatureis the limiting factor. They suit a grower building under cover for the first time on a tropical site,an operation extending a multi span block along the same gutter line, and projects where the houseships as a flat pack and is assembled by a local crew. A gothic multi span house built for snowshedding is described in the gothic multi span snow shedding greenhouse page.
Standards for structures and components are published by DIN. Global greenhouse production news is published by HortiDaily. A gothic multi span house built for cut flowers is described in the gothic multi span greenhouse for cut flower cultivation page.
Through the stack effect. Warm moist air rises along the steep gothic pitch and leaves at thecrown, drawing cooler air in at crop height through the side openings. The shape does the work, sothere is nothing to run and nothing to fail.
Because tropical rain arrives in a short heavy burst rather than spread across the year. A guttersized on an annual average overflows into the house at the moment the water arrives, which is thecondition the house exists to keep off the crop.
The galvanized steel frame is rated for 15 to 20 years under normal growing conditions. The filmcover is replaced on its own cycle, and the vent openings, gutter line and fixings are serviced eachseason.
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 rainfall and wind data. We reply with a layout drawing and a full quotation.
