Steel structure.

The skeleton that carries everything

Every system in a greenhouse — the glass, the screens, the heating pipes, the irrigation, the crop itself hanging heavy with fruit — ultimately rests on the steel sub-structure. Columns stand on the grid, trusses span between them, and girts run horizontally along the facades to carry the side cladding and take the wind pressure on the walls. No steel runs horizontally in the roof at all: a Venlo has no purlins, and the only horizontal members up there are the aluminium gutter and ridge, with the glazing bars running vertically between them. That absence is part of why a Venlo roof casts so little shadow. None of it is a generic frame. Local wind and snow loads, the weight of the cladding and screens, and the crop and hanging-gutter loads are all fed into the engineering so that spans and section sizes are matched to what the greenhouse will actually face over its decades of service.

Standing the frame up is only half the problem. A grid of columns and trusses will carry weight quite happily and still lean over in a storm, so the greenhouse is squared by a separate stability system: bands of crossed steel rods repeating along the length of the house, and horizontal ties above them linking every gutter line across the width. The rods work in tension only — a rod can pull but it cannot push — so both diagonals of every cross are installed, one for each direction the wind arrives from. Neither is spare.

One consequence is worth knowing before the layout is drawn. A bracing band cannot be interrupted by a door or an opening. Where the two collide, it is the opening that moves — one of the few places in a greenhouse where the structure genuinely outranks the floor plan.

Because a greenhouse stands in a warm, humid environment for twenty years or more, corrosion protection is fundamental rather than cosmetic. The steel is hot-dip galvanised, immersed in molten zinc so that every surface — inside hollow sections included — is coated and protected. That single choice is a large part of why a well-built Dutch greenhouse keeps performing for so long: the skeleton does not rust away beneath the glass.

The steel grid is dimensioned around the cultivation system, not the other way round. Span widths, gutter heights and column positions all follow the crop layout — the spacing of the rows, the height the crop needs to grow, the paths the internal transport will take — so the structure serves the growing rather than obstructing it. A tomato crop on hanging gutters, a lettuce system on moving benches and a potted-plant operation each imply different geometries, and the steel is engineered accordingly.

Sequencing also matters on site. Ventilation mechanisms and future provisions are mounted to the trusses before erection, while the work can still be done safely at low level, so that once the frame is raised the structure is already prepared for the stages that follow. The result is a skeleton engineered for the specific climate, crop and lifespan of the project — strong where it needs to be, and no heavier than it should be. Get in touch to discuss the structural engineering behind your greenhouse.