The Main Greenhouse Types in Use
Three broad categories cover the majority of protected structures on Polish horticultural holdings: glass greenhouses (most commonly the Venlo type), single- or multi-span foil tunnels with a metal or heavy-wire frame, and low polytunnels made of lightweight hoops covered with perforated or non-woven film. Each serves a different segment of the production calendar and comes with distinct infrastructure requirements.
Glass Venlo Greenhouses
The Venlo design — developed in the Dutch Westland region — became standard across Northern European commercial horticulture through the second half of the twentieth century. It uses narrow, standardised bays of 3.2 m or 6.4 m width, with single-slope glass panels seated in aluminium profiles. The gutter-connected multi-span layout allows almost unlimited horizontal expansion while maintaining a single internal climate zone.
In Poland, Venlo structures are found primarily on large-scale tomato and cucumber operations where year-round production is the goal. The glass covering transmits more light than double-skin foil, which matters most in the short days of December and January. The tradeoff is a higher upfront investment per square metre compared to foil construction, and a greater sensitivity to hail damage without protective netting.
Polish building regulations (PN-EN 13031-1) specify design loads for greenhouse structures, including snow loads that range from around 0.7 kN/m² in the lowland centre of the country to over 1.5 kN/m² in the southern mountain foothills. Structures intended for southern voivodeships must be specified accordingly.
Foil Tunnels with Rigid Frames
Multi-span foil greenhouses with galvanised steel frames represent the most common mid-scale investment in Polish protected horticulture. The covering is typically a double-layer polyethylene film with an air gap that provides thermal insulation broadly equivalent to a single glass pane. Inflation systems maintain the air gap and are standard on structures above 500 m².
The main advantage of foil over glass at this scale is installation speed and the ability to replace the covering material in sections. UV-stabilised polyethylene films rated for four-year outdoor exposure are the industry norm; some diffuse-light formulations aim to reduce the shadow cast by the structure itself and improve light distribution at the crop canopy level.
Side-wall design varies significantly. Permanent brick or block walls on the perimeter retain heat more effectively in winter but reduce summer ventilation flexibility. Roll-up side walls — where the foil can be wound up to expose a mesh-screened opening — are preferred on structures used for heat-tolerant summer crops such as pepper or aubergine.
Low Polytunnels
Low polytunnels are a separate category from the span structures described above. They are typically 0.6–1.2 m tall, made from bent wire or lightweight polypropylene hoops set directly over a bed or row, and covered with perforated polyethylene film or spunbonded non-woven fabric (agrotextile). They do not require a foundation and can be erected or removed within a day.
Their primary use in Poland is to extend the outdoor growing season for strawberries, early salad crops and brassicas. A covering of 50 g/m² non-woven fabric provides protection down to roughly −3 °C and simultaneously transmits around 80% of photosynthetically active radiation. Ventilation under low tunnels is managed by partially removing or cutting the cover as temperatures rise in April and May.
Structural Considerations for Polish Conditions
Poland's climate presents a distinctive combination of challenges for greenhouse structures. Snowfall is moderate across the central plains but can be heavy and wet in the foothills of the Carpathian and Sudeten ranges. Wet snow loads are particularly demanding because the snow does not slide off easily in mild, damp conditions. The standard EN 13031-1 sets out calculation methods for snow and wind loads specifically for protected horticultural structures and is the reference document for structural design in Poland.
Wind exposure is a secondary concern on most lowland Polish sites, but structures adjacent to forest edges or on elevated ground should account for localised wind acceleration. Corner bays of multi-span structures typically carry higher loads than internal bays and are reinforced accordingly in standard designs.
Foundation Types
Most commercial foil and glass structures in Poland use driven galvanised steel posts anchored directly into the ground — a method that is cost-effective and reversible, though it requires firm, unfrozen soil during installation. Concrete strip foundations are used where the soil is sandy or where the structure must carry additional loads such as gutter-hung irrigation systems or suspended thermal screens.
Polycarbonate as an Alternative Covering
Twin-wall and multi-wall polycarbonate sheets occupy a niche between glass and foil. They offer better thermal insulation than single-layer glass and greater longevity than polyethylene film, but they yellow over time as UV stabilisers break down. On structures where the covering is expected to last ten years or more without replacement, polycarbonate is used primarily for side walls and ridge sections rather than the main roof area.
Selection Criteria in Practice
Growers selecting a structure type typically weigh the following factors:
- Target crop and its light requirements (tomatoes and cucumbers benefit significantly from high light transmission)
- Length of intended season (year-round production requires better thermal performance than an April–October operation)
- Site conditions — local snow load zone, wind exposure, proximity to groundwater
- Available capital for upfront investment versus ongoing maintenance cost
- Labour availability for seasonal tasks such as foil replacement
For operations expanding from an existing outdoor base, low polytunnels and single-span foil tunnels offer a lower entry cost with measurable yield and season-extension benefits. Fully climate-controlled glass or foil Venlo structures are typically part of a deliberate move to year-round commercial production.
