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Structural and climate design

Structure and facilities, simulated from design to harvest

Every stage of a Better Farm greenhouse, from design to construction, answers to two families of standards. The international ones: NEN 3859, guidance from the Food and Agriculture Organization of the United Nations and the recommendations of the US National Greenhouse Manufacturers Association. The Iranian ones: standard 15565 of the Iranian National Standardization Organization, and Publication 472 of the country's Plan and Budget Organization.

Before anything is fabricated, the house is modelled from structure to harvest — the frame under its loads, and the climate inside it through the seasons — to find what this crop on this site actually needs. A problem found in the model is solved on paper; the same problem found in the second season is solved in steel and glass.

Finite element output showing the deformed shape of a Venlo greenhouse roof grid under load, colour-mapped by displacement

What is optimised

Structure and equipment are designed as one facility, for the most performance at the least cost — which in practice means the least input and, above all, the least energy.

The design is optimised in a fixed order: grow the crop on the least energy, then on the least water and fertiliser, then raise the yield, then the profit. The four are not independent, and the order matters. Energy and water are the operating costs that compound over twenty years; yield is what they buy.

Structural analysis

Finite element modelling covers the full bay set — columns, trusses, gutters, bracing and connections — under the load combinations the project is built to. That includes the loads a greenhouse has and an ordinary building does not: crop load hanging from the gutters, installation load from screens, heating pipe and lighting, and the concentrated vertical load of a person working on the roof.

Site wind and snow figures come from the thirty-year record established at the feasibility stage, not from a national average. Seismic figures follow the Iranian code where the site requires it.

The load cases, and the one that is always missed

The structure is analysed as the full bay set rather than as a single frame, against six load cases, because a repeating structure shares load between bays and a single-frame check misses what the neighbours do.

Diagram Six load cases on one bay

  • Dead The structure’s own weight — the smallest of the six.

  • Wind Governs, as suction lifting a light, smooth roof and wind racking the frame.

  • Snow Worst when it lies unevenly in the valleys, one side loaded and the other clear.

  • Crop A crop on hanging gutters, permanently on the aluminium.

  • Installation A half-built frame under a lifting load is a different structure from a finished one.

  • Concentrated Pipe, screens, lighting, transport and people at height — hung over twenty years.

Wind governs, and governs as uplift. The sixth case is the one most often missing from a greenhouse design — because it arrives after handover.

Dead load. The steel, the aluminium and the glass. The smallest of the six, and the only one a greenhouse shares with an ordinary building in any meaningful way.

Wind. The governing case, and it governs as uplift. A glasshouse is light, large and smooth, standing in the open — the wind tries to lift it and rack it, not push it down. This is why the foundations resist uplift rather than bearing, why the bracing is not optional, and why the gable columns are the heaviest sections in the building.

Snow. Governs where it falls, and governs a 26° roof differently from a flat one: snow slides off a slope until it does not, and the case that matters is snow held in the valleys at the gutters, unevenly, with the roof partly cleared and partly loaded.

Crop. A tomato or cucumber crop on a hanging gutter system is a substantial, permanent, distributed load applied directly to the aluminium. It is not a small number, and it is applied for the whole season, every season.

Installation. The loads during erection, which on a light structure are often worse than the loads in service — a partly braced frame with a lifting load on it is a different structure from a finished one.

Concentrated vertical load. The one that is always missed. Over twenty years a grower hangs things: heating pipe, screen mechanisms, lighting rails, internal transport, CO₂ distribution, hanging gutters, and at some point a person on a trolley working at height. Most of the load a greenhouse ends up carrying is added after it was handed over, by people who assume the building will take it. Designing for the bare house and equipping it afterwards puts the structure outside its design case, and nothing about it looks wrong until something is hanging from it.

Model of the energy screen and canopy system carried on the greenhouse grid
Better Farm · design model An energy screen and canopy system modelled on the grid. Every item a grower may add later is a load the structure has to be designed for now.

Climate and airflow

Air exchange through the ridge vents is assessed against structure height and vent dimension, which together govern the heat-exchange capacity once the vent area is fixed.

Heating and cooling demand is simulated across the thirty-year climatic average for the site. That simulation is what decides between pad-and-fan, a semi-closed system and geothermal — the last of which runs at a coefficient of performance of roughly 3 to 4 where the ground supports it.

Reference

Specification

Parameter Typical range
Standards
Structure NEN 3859 — commercial production greenhouses
Agricultural guidance FAO; NGMA (US National Greenhouse Manufacturers Association)
Iranian standards INSO 15565; Publication 472, Plan and Budget Organization
Galvanising ISO 1461
Structural model
Method Finite element model of the full bay set, not a single frame
Load cases Dead, wind, snow, crop, installation, concentrated vertical
Wind and snow From the site record, not a national average
Climate model
Basis Thirty-year meteorological average for the site
Decides Pad-and-fan, semi-closed or geothermal
Optimised for Least energy, water and fertiliser; then yield; then return

Values for the standard Better Farm bay set, referenced to the governing codes. Project values are confirmed against the site's wind, snow and seismic figures, the crop and the equipment schedule before fabrication is released.

Design notes

What decides the detail

  • Crop load is a real load

    A tomato crop hanging from the gutters is several kilograms per square metre applied to a structure designed to be as light as possible.

  • Simulate to harvest

    Modelling the structure alone answers whether it stands up. Modelling through to harvest answers whether it should have been built that way.

  • Energy before yield

    Input costs compound across twenty years of operation; a yield gain bought with energy is usually a loss with a lag.

  • Two standards families

    NEN 3859 governs the structure; FAO, NGMA, INSO 15565 and Publication 472 govern the agricultural and national requirements around it.

Reference

Common questions

  • Which standards govern greenhouse structural design?

    NEN 3859, the Dutch standard for commercial production greenhouses, is the governing structural code. It sets requirements for strength, stiffness, stability and durability against load cases specific to greenhouses — crop load, installation load and concentrated vertical load alongside wind and snow. Galvanising follows ISO 1461. Alongside these, Better Farm designs answer to guidance from the Food and Agriculture Organization and the US National Greenhouse Manufacturers Association, and to the Iranian national standard INSO 15565 together with Publication 472 of the Plan and Budget Organization.

  • What is optimised in a greenhouse design?

    Least energy first, then least water and fertiliser, then yield, then return — in that order, because operating inputs compound across a twenty-year service life while yield is what those inputs buy. Structure and equipment are designed together for the highest performance on the least input, with every stage from design through to harvest simulated so that the requirements of the specific crop are identified before construction rather than during operation.

  • Which loads is a commercial greenhouse structure designed for?

    Six, analysed by finite element modelling of the full bay set rather than a single frame, because a repeating structure shares load between bays. Dead load — steel, aluminium and glass, the smallest of the six. Wind, which governs, and governs as uplift rather than pressure because a glasshouse is light, large and smooth and stands in the open. Snow, which governs a 26° roof differently from a flat one and matters most when it is held unevenly in the gutter valleys. The crop hanging from the gutters. The loads during erection, which on a light structure are often worse than in service. And concentrated vertical load from the equipment added over twenty years of operation.

  • Why is a greenhouse analysed as a full bay set rather than a single frame?

    Because the structure repeats, and repeating structures share load. A frame checked on its own behaves as if its neighbours were not there; in the building, the gutters, bracing and roof plane tie every bay to the next, so a load on one bay is partly carried by the bays around it — and a load case such as uneven snow in the valleys only exists across several bays at once. Modelling the full set shows both where the structure can be lighter and where a single-frame check would have missed a problem.

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