# Steel Structure

> Part of: [Greenhouse Construction](/greenhouse-construction.md) · Provider: [DutchGreenhouses](/)

The steel sub-structure is the skeleton every other system hangs from: glass, screens, heating pipes, irrigation and the crop itself. Columns, trusses and facade girts carry the loads, a crossed-rod bracing system holds the frame square, and hot-dip galvanising protects all of it for decades.

## Facts
| Property | Value |
|---|---|
| Members of the frame | Columns, trusses and girts member types |
| Column families | 6 families |
| Stability system | Vertical X-bracing plus horizontal wind ties categorical |
| How bracing rods work | Tension only categorical |
| Design loads fed into the frame | 4 load types |
| Corrosion protection | Hot-dip galvanising method |
| Span between column rows | 8, 9.6 or 12.8 m |
| Bay spacing between trusses | 4–5 m |
| Governing standard | EN 13031-1 standard |

Structure

# Steel structure.

    The skeleton that carries everything.

## 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.

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## FAQ
**What holds a greenhouse frame square against wind?**
A bracing system, not the columns alone. Bands of crossed steel rods repeat along the length of the house, and horizontal ties above them link every gutter line across the width. Without it a grid of columns and trusses would simply lean; the bracing is what turns it into a stable box.

**Why are bracing rods installed in pairs if only one works?**
Because they act in tension only. A rod can pull but not push, so one diagonal of each X takes the load when wind comes from one side and the other takes it when the load reverses. Both are needed, and neither is spare.

**Can a door be put wherever the layout wants it?**
Not if it would interrupt a bracing band. The stability system is set out first and the opening is adapted around it, because a band with a hole in it is no longer a load path. This is one of the few places where the structure genuinely outranks the floor plan.

**What are the members of a greenhouse steel frame?**
Columns, trusses and girts. Columns stand on the grid and set the gutter height; trusses span between them and carry the roof, crop wires and screen installations; girts run horizontally along the facades, carrying the side cladding and taking wind pressure on the walls back into the frame.

**Is a greenhouse column always the same part?**
No. Six families exist — gable, internal gable, interior, bracing, side wall and side intermediate — and position decides which one applies. The family then decides the profile, whether the column takes girt connections, and whether it carries screen strips. There is no separate corner column: where an end wall meets a side wall, the end wall governs.

**Is a truss a single member?**
No, it is an assembly. Upper and lower chords, tension and compression diagonals, end pieces and connection plates each have their own profile and role, and the counts of tension and compression diagonals are not necessarily equal. Treating a truss as one beam hides the design.

**Are there purlins in a greenhouse roof?**
No. No steel runs horizontally in a Venlo roof at all. The only horizontal members up there are aluminium — the gutter and the ridge — and between them the glazing bars run vertically up the slope carrying the glass. That is a real difference from general steel building construction, where roof purlins are standard, and it is part of why the roof casts so little shadow.

**What loads is a greenhouse frame designed for?**
Site wind and snow, the cladding and screen installations, and the crop. A high-wire tomato or cucumber crop hangs its entire weight from crop wires suspended off the trusses, so crop load is a design input in a way it never is for a normal building. Installation loads during construction are checked as well.

**Why is greenhouse steel hot-dip galvanised rather than painted?**
Because immersion in molten zinc coats surfaces a brush cannot reach, including the inside of hollow sections. A greenhouse stands in warm, humid air for its whole working life, and corrosion starting inside a closed section is invisible until it matters. The zinc layer is why a well-built structure keeps performing under the glass.

**What decides the span and column positions?**
The cultivation system, not the structure. Row spacing, the height the crop needs, and the paths internal transport will take set the grid; the steel is then dimensioned to suit. A tomato crop on hanging gutters, lettuce on moving benches and a potted-plant operation each imply different geometries.

## Related
[Greenhouse Construction](/greenhouse-construction.md) · [Foundation](/greenhouse-construction/foundation.md) · [Aluminium System](/greenhouse-construction/aluminium-system.md) · [Screening](/screening.md) · [Truss (Trellis Girder)](/glossary/truss.md) · [Column](/glossary/column.md) · [Girt](/glossary/girt.md) · [Vertical X-Bracing](/glossary/bracing.md) · [Horizontal Wind Tie](/glossary/wind-tie.md) · [Screen Strip](/glossary/screen-strip.md) · [CASTA](/glossary/casta.md) · [Galvanization](/glossary/galvanization.md) · [Bay and Span](/glossary/bay-and-span.md) · [EN 13031](/glossary/en-13031.md) · [ISSO 88](/glossary/isso-88.md) · [Crop Wire](/glossary/crop-wire.md) · [Wind and Snow Load](/glossary/wind-and-snow-load.md)