Greenhouses come in many shapes and sizes: plastic polytunnels, gothic arches, multi-span and wide-span structures. One of them has become the most recognised greenhouse in the world. The Venlo greenhouse, known outside the Netherlands as the Dutch greenhouse, is a multi-span glass greenhouse: a row of narrow pitched glass roofs with a gutter between each pair, standing on a steel grid of columns and trusses, with an aluminium roof system on top. It is named after Venlo, the Dutch town where the type was first built.
Over the last decades it became the standard for professional horticulture. It is simple, light and efficient to build, and it takes every climate system a grower needs: screening, ventilation and heating. Built correctly, a Venlo greenhouse outlasts a generation.
I have been in the greenhouse business for almost 15 years. I have sold greenhouses, managed their construction, built them myself and worked in them as a teenager. This series walks through how a Dutch Venlo greenhouse is put together, in the order it is built: parameters, foundation, steel structure, aluminium system, glass covering, ventilation and screening. Before any of those parts, four parameters decide what the greenhouse is.
The grid
Mapping out a greenhouse starts with a structural grid. The grid has two directions.
The first is the truss, also called the span or bay. It is the distance between two rows of columns, and the truss bridges it. The common sizes are 8 metres, 9.6 metres and 12.8 metres. The 8 metre truss is used most, especially for vine crops such as tomatoes, peppers and cucumbers.
The second is the section: the distance between one truss and the next, along the gutter. It is the free space between one column and the next in that direction. Typical sections are 4 metres, 4.5 metres and 5 metres.
Together, truss and section give the column grid. Every column position is a point on that grid, and every point on that grid becomes a hole in the ground. The glossary entry on bay and span has the short version.
The height
Greenhouses have grown taller over the last thirty years. A gutter height of 4.5 metres was the standard in the 1980s and 1990s. The 2000s passed 5 metres. Today 6 metres, about 20 feet, is the normal production height, and greenhouses are now being built at 7 metres.
Height is measured to the gutter, not to the ridge: the post height and the free space under the gutter are what the crop, the screens and the lighting have to live with. The ridge sits higher. A greenhouse built at 6 metres to the gutter is around 1.2 metres taller at the ridge. More on why height matters is under gutter height.
The footprint
With a grid and a height, the footprint can be drawn. A question I get often is how big a greenhouse can be. My answer is around 15 hectares as a single building.
The technical limits are rainwater discharge and the thermal expansion of steel and aluminium. A roof that long has to get its water off fast enough during a downpour, and the structure has to be allowed to grow and shrink with temperature without cracking anything.
The real limit is not technical. It is workability. How far does staff walk to reach a toilet? How long is a single row before the person working it loses motivation? How does the grower keep oversight? Those questions set the size of a greenhouse long before the steel does.
The loads
The Venlo type is built around the world. I have built in the Netherlands, in southern Europe, in the United States and in the Gulf, each with its own conditions and its own regulations. Some sites bring heavy snow. Some bring high winds. Some bring earthquakes. The soil varies too: sand, clay, gravel, peat.
Then there are the loads the greenhouse puts on itself. In modern vine crops the plants hang from the structure on crop wires and cultivation gutters, so the full weight of a tomato crop is carried by the trusses. Roof washers run over the roof on the gutters. Screens pull on the columns. All of it has to be carried.
These factors together determine the configuration of the greenhouse and how strong it must be. The structural calculation works through them case by case, and the design is optimised to use the minimum material that still carries every load. The Dutch standard figures for wind and snow do not transfer abroad: a greenhouse built outside the Netherlands is calculated on local wind, snow and seismic data.
That is the greenhouse on paper: a grid, a height, a footprint and a set of loads. Wind, snow, the crop hanging from the gutters, the roof washer on the roof. Every one of those loads has to go somewhere, and they all end up in the same place: a few hundred holes in the ground. That is part two, the foundation.
Planning a commercial greenhouse yourself? Let’s plan some time together.
