How many years does a polytunnel last?
The film and the structure have to be considered separately. According to the University of Connecticut, UV-stabilised greenhouse film carries a manufacturer's warranty of 4 years or more, while cheap seasonal film lasts one season; we give a 3-year warranty on the film on our tunnels. The life of a steel structure depends on the zinc coating (Z275 means at least 275 g/m² of zinc on both surfaces of the sheet together), on how corrosive the surroundings are, and on whether the structure carries snow and wind loads.
A polytunnel consists of two parts that age at completely different rates: the film and the steel structure. The film is replaced every few seasons. The life of the structure is determined by the material, the anti-corrosion coating, the design and the conditions in the field. So the question “how many years” has to be answered separately for each.
How many years the film lasts
Polyethylene film is damaged mainly by sunlight and heat. A University of Connecticut guide describes two classes of film:
| Film class | Thickness per UConn | Life per UConn |
|---|---|---|
| seasonal (co-poly) | 3, 4 or 6 mil (about 76–152 µm) | one season |
| UV-stabilised greenhouse film | 6 mil (about 152 µm) | manufacturer’s warranty of 4 years or more |
We cover our tunnels with single film 150–200 µm thick. We give a 3-year warranty on the film.
What shortens the life of the film
The University of Connecticut lists:
- crop protection products and chemicals from pressure-treated timber,
- the film heating up where it touches the structure.
We cover choosing the thickness, UV stabilisation and additives in more detail in our guide to choosing tunnel film.
What the life of the structure depends on
We do not give a number of years for the steel structure. It depends on several factors, which we describe below.
Z275 zinc coating
Zinc protects steel from corrosion. The Z275 designation comes from the EN 10346 standard. SSAB gives for Z275 a minimum coating mass of 275 g/m² on both surfaces together and an indicative thickness of about 20 µm on each surface. ArcelorMittal converts it the same way: Z275 is the standard coating for construction products, corresponding to about 0.02 mm of zinc on each surface.
The legs, anchors and hoops of our tunnels have a Z275 coating:
| Component | Steel |
|---|---|
| legs and anchors | E370+Z275 (about 10% stronger than S350+Z275, at the same price) |
| hoops (arches) | S350+Z275 |
How corrosive the surroundings are
Zinc is not lost at the same rate everywhere. ISO 9223 divides atmospheres into corrosivity categories from C1 (very low) to CX (extreme). According to a summary by HDGASA, a galvanisers’ association, based on that standard, the category depends on factors such as how long the surface stays wet, pollution by sulphur compounds and chlorides carried on the wind from the sea. The summary also points out that the category descriptions are only a general guide and need to be checked on site.
That is why the same structure can age differently in different fields.
Tube profile
The strength of the structure depends on the profile of the tube from which we bend the hoops. We offer round tubes Ø40, Ø50.8 and Ø60.3 mm and oval tubes 80×40 and 90×50 mm. The 90×50 oval tube gives +29% strength at a similar price.
Arch shape and snow
The University of Missouri states that gothic arches as a rule cope better with heavy snowfall than round ones. The pointed ridge helps snow slide off, and the weakest point of a round arch is its almost flat top. The Cornell University guide adds that gothic tunnels, being more exposed to wind, need additional bracing.
Hoop spacing matters too. According to the University of Missouri, with the same tube diameter, a tunnel with hoops every 4 feet (about 1.2 m) is clearly stronger than one with 6-foot (about 1.8 m) spacing.
We build both types of arch. The choice depends on the location and the crop; we agree it during a visit to the customer.
Anchors and foundations
We make anchors in lengths of 700, 850 and 1000 mm, and legs for multibay tunnels in lengths of 2.5–3.5 m. We set tunnels up to 5 m high on upset anchors (1.25–2.0 m).
What you can do to make your tunnel last longer
| Threat | What to do | Source |
|---|---|---|
| snow on the roof | clear snow from the ridge, e.g. by pulling a rope over the roof or sweeping it off the hoops | University of Missouri |
| wind | close the sides and end walls in strong wind | Cornell University |
| chemicals | limit contact between the film and chemicals | University of Connecticut |
| corrosion | assess the conditions on site, e.g. look at the state of galvanised structures in the area | HDGASA (ISO 9223) |
The University of Missouri also points out that replacing the film is much cheaper than replacing steel hoops.
Cornell states that wind is the greatest enemy of a high tunnel, and that it is worth choosing a site that limits exposure to wind.
Summary
| Part of the tunnel | What its life depends on | What we offer |
|---|---|---|
| film | film class, UV stabilisation, chemicals, conditions | film 150–200 µm, 3-year warranty on the film |
| steel | zinc coating, corrosivity of the surroundings | E370+Z275 (legs, anchors), S350+Z275 (hoops) |
| arch | shape, hoop spacing, tube profile | round or gothic arch, round tubes and oval 80×40, 90×50 |
| foundations | length and type of anchors | anchors 700 / 850 / 1000 mm, upset anchors for tunnels up to 5 m |
We match the structure to the field during a visit to the customer. Start with the configurator or call us: +48 512 208 808.
Sources
- Plastic Film Update — J. W. Bartok Jr., University of Connecticut, UConn IPM (updated 2013) (accessed 11 October 2026)
- Metal coated HSLA steels, EN10346:2015 — SSAB (table of zinc coatings) (accessed 11 October 2026)
- Explanatory Notes — Cold formed sections — Dimensions of sections, ArcelorMittal Orange Book (accessed 11 October 2026)
- Hot Dip Galvanized Information Sheet No. 8: Corrosion of Zinc – Corrosivity of Atmospheres (HDGASA, based on ISO 9223:2012) (accessed 11 October 2026)
- Snow Removal From High Tunnels — D. Trinklein, University of Missouri, Missouri Environment & Garden (accessed 11 October 2026)
- Structures — Cornell High Tunnels (Cornell University) (accessed 11 October 2026)