TECHNICAL 03 · LOADS
Snow load: from ground figure to a purlin that does not sag.
A snow load on a greenhouse is not one number. It is a ground figure, a roof shape factor, an exposure factor and a decision about whether the house is heated. Get the chain wrong and the frame is either unsafe or expensive.
EN 1991-1-3 gives the ground snow load for a location; EN 13031-1 is the greenhouse design standard and carries its own snow provisions, including an annex on snow load. The structural designer combines them with the roof geometry. We do not substitute for that calculation, but we do need its output.
| Step | What happens | Who does it |
|---|---|---|
| 1 | Ground snow load for the site (kN/m² or kg/m²) | Structural engineer |
| 2 | Shape coefficient for the roof (curved, sawtooth, multi-span) | Structural engineer |
| 3 | Exposure / thermal coefficient (heated or not, sheltered or not) | Structural engineer |
| 4 | Roof snow load, plus drift where geometry causes it | Structural engineer |
| 5 | Member loads: arch, purlin, gutter | Structural engineer |
| 6 | Sections, spacing and anchors | Engineer, then us to supply |
If steps 1–5 arrive as one figure (“40 kg/m² roof load”), that is enough for us to quote.
What changes in the frame
- Arch wall thickness before arch section: 2.0 → 2.5 mm often buys more than a wider oval.
- Arch spacing: 1.0 m instead of 1.2 m adds arches but removes the weak point.
- Purlin depth and spacing: snow sits on the cover, and the cover sits on the purlin.
- Gutter: snow sliding into a gutter is a point load at the bracket.
- Anchors: snow load is downward, so it does not pull anchors out — but the combination with wind does.
The mistake we see most
Upgrading the arch and leaving the purlin at 1.2 m. The frame looks heavier but the roof still sags between arches, and the buyer concludes the steel is poor. Snow is a system load, not a single-member load.
Curved roofs shed, but not always
A curved film roof sheds snow better than a flat one, which is why tunnel and multi-span houses often carry less snow than their span suggests. Two caveats: shedding depends on the cover being smooth and the house being warm enough to slide, and snow that slides lands in the gutter. A blocked gutter turns shedding into ponding.
Read next
Pages that answer the question this page raises.
- 08.04Wind loadGreenhouse wind load: pressure and uplift, exposure, bracing, anchors and the open-side ca→
- 08.16EN 13031-1EN 13031-1 greenhouse design standard explained: scope, loads, snow annex, and what a supp→
- 07.07KazakhstanGreenhouse frames for Kazakhstan: rail via Dostyk, heavy snow loads, arch selection and an→
- 04.02.03Oval tube 40×8040×80 mm oval greenhouse tube, wall 1.5–2.5 mm, bent arches and straight lengths, galvanis→
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