If you have searched for a polycarbonate polytunnel in the UK, you probably want the long walk-through shape of a tunnel without the polythene film that goes baggy, tears and needs re-skinning every few years. That is a sensible instinct, and the category exists: a galvanised steel arch frame glazed with rigid twin-wall polycarbonate panels rather than stretched film. The trouble is that "polycarbonate polytunnel" covers everything from a £850 flat-pack with spring clips to a £2,960 specialist build engineered for exposed sites, and the gap between them is mostly invisible in a product photo. This guide explains what the term actually means, why a gardener chooses rigid panels over film, the handful of build details that separate a tunnel that lasts from one that pops apart in a March gust, a realistic cost band, and who is better off keeping a film tunnel after all.
What a polycarbonate polytunnel actually is
Take the arched profile of a classic polytunnel, swap the polythene cover for cellular twin-wall polycarbonate sheet, and bolt those sheets to a galvanised steel frame. That describes the whole idea. Sellers in this category typically build on a steel arch with twin-wall polycarbonate, two doors at the ends and upper sections for ventilation. Twin-wall means two skins of polycarbonate with an air gap between them, which is where the insulation comes from compared with a single sheet of glass or a single layer of film.
The shape gives you headroom along a long growing run, the same reason allotment holders like film tunnels. The glazing gives you a rigid shell that does not flap, does not need tensioning and does not have to be replaced as a consumable. Light behaves differently too. Polycarbonate scatters light rather than letting it pass straight through, and category sources commonly cite light transmission of roughly 70 to 83 per cent for polycarbonate against about 90 per cent for glass, with the diffused light reducing the risk of leaf scorch on a bright day. Treat those figures as a category norm rather than a measured promise from any single maker.
Why choose rigid polycarbonate over a film polytunnel?
It comes down to the cover. A film polytunnel costs less to buy, but the polythene wears out. First Tunnels, one of the larger UK polytunnel suppliers, states that a commercial-grade 720 gauge (180 micron) cover "will usually last for at least 4-5 years" before it needs replacing, with some lasting ten years or more under careful maintenance. Rigid twin-wall removes that re-skinning job entirely, which is the core appeal for anyone tired of the ladder, the wind and the re-tensioning.
The Royal Horticultural Society describes a film polytunnel as "a highly cost-effective means of growing summer crops" while noting it is "rather unsightly and not usually economical to heat and keep frost-free over winter". The RHS adds that film tunnels suit hardy winter crops such as lettuce but "cannot be used for overwintering tender plants". Rigid twin-wall, with its insulating air gap, holds a little more warmth and looks more like a permanent garden structure. If you want something closer to a greenhouse in feel but keep the tunnel footprint, this is the trade you are making. Our polytunnel vs polycarbonate greenhouse guide weighs that trade over ten years.
When film still wins
- You want the lowest possible upfront cost and are happy to re-skin every four to five years.
- You need a very large covered area where rigid glazing becomes expensive fast.
- You are growing seasonal summer crops and do not mind the appearance.
If that describes you, our heavy-duty polytunnel buyer's guide covers frame gauge and anchoring for film tunnels, and the polytunnel alternatives guide is the right read if you are weighing leaving the tunnel format altogether.
What to look for: screw-fixed panels versus spring W-clips
This single detail decides whether your tunnel survives a windy site. The cheapest aluminium-and-polycarbonate builds hold each panel with spring clips, often called W-clips, that grip the sheet under tension. In moderate UK wind those clips can lose tension and the panels work loose. Owners on gardening forums describe panels blowing out and resort to silicone, extra clips and even bamboo canes braced against the sheets to keep them in place. Spring clips assemble quickly, and that speed counts as their only real advantage.
Screw-fixed or button-fixed glazing is the durable approach. The panel is mechanically held to the frame rather than relying on spring tension. Trade guidance for polycarbonate tunnels even advises that on windier sites you should "increase the frequency of the fixing buttons on the sides". When you compare two listings, find out how the panels attach before you compare anything else. A screw fix on a 6mm twin-wall sheet behaves very differently from a clip in a January gale.
The check, in one line
Ask the seller: are the panels screwed or button-fixed to the frame, or held by clips? If the answer is clips, the price needs to reflect a structure you may have to brace yourself.
What to look for: closed steel-arch frame and close arch spacing
The frame carries the wind load, so its profile and spacing matter as much as the glazing. Category frames are galvanised steel tube, and the range is wide. Published examples run from light 20x20mm galvanised tube on budget models up to 60x20mm box section on heavier builds. A closed box or rectangular hollow section resists bending better than an open single-skin hoop of the same wall, and arches set closer together leave each panel less unsupported area to flex.
Two things are worth reading off a spec sheet.
- Section shape and size. A closed rectangular hollow section, quoted with both dimensions such as 40x20mm, tells you more than a vague "steel frame".
- Arch spacing. Closer arch centres mean each polycarbonate panel spans less, which keeps the shell rigid. Our SteelRoot frame, for example, sets arches at 0.67m centres for that reason.
None of this needs storm-rating language. Heavier closed section and closer spacing simply give the panels less room to move, and that is what keeps screw-fixed glazing where you put it.
What to look for: ground anchors included, base recommended
Ground anchors should come in the box, not as an upsell. In this category they usually do. Sellers ship T-shaped anchors that drive directly into the ground, with one listing specifying anchors that are "'T' shaped and 30cm long" per frame end, plus optional angle brackets if you want to bolt the frame onto a solid base instead. The house position at Waldenhaus follows the same logic: ground anchors are standard, so no concrete foundation is required. For extra stability, we recommend a firm, level base.
So the look-for is twofold. Check that anchors are included rather than sold separately, and check whether the maker also offers brackets for a paved or timber base. A level base repays the effort on any rigid tunnel, because a twisted frame loosens panels over time.
What to look for: ventilation you will actually have
A rigid tunnel seals tighter than film, which helps in winter and turns into a hazard in July. The RHS sets out the rule of thumb: roof and ridge ventilation should equal roughly 20 per cent of floor area, "one square metre of ridge ventilation for each five square metres (20%) of floor area", which gives about one complete air change every two minutes. Smaller structures should ideally have an even higher proportion. The same guidance warns that once temperatures build above roughly 27°C (81°F), plant damage can occur.
Watch the catch with budget polycarbonate tunnels, where ventilation is often thin and sometimes costs extra. On some models "ventilation windows are not standard but can be ordered separately". When you price a tunnel, add the vents you need to hit that 20 per cent figure, then compare. A tunnel that looks cheap can land at the same number once it is actually ventilated. An auto-vent that opens on its own removes the daily worry of a sealed structure cooking your tomatoes while you are at work, which is why an auto-opening vent window earns its place on any rigid tunnel.
Realistic cost band for a polycarbonate polytunnel
Pricing in this category spreads wider than newcomers expect. Mainstream UK polycarbonate-polytunnel models run roughly £850 to £2,050 on a footprint around 2.6m to 3m wide with 6mm twin-wall, with the figure climbing as you add length. Two Wests lists models from £849.99 to £2,049.99 across lengths from 2m to 12m on an 8.5ft (2.6m) wide footprint. A single mid-range data point from Gardening Naturally is a 3m-wide 6mm tunnel at £1,090, with double doors, a key lock, two vent windows, a 2-year warranty on the frame and a 5-year warranty on the polycarbonate.
The ceiling sits far higher. Polycrub, the Shetland specialist built for exposed island sites, publishes prices "from £2960 including VAT, excluding delivery". That is not a typical garden price, but it shows where the category tops out once a build is engineered for high wind.
| Tier | Typical price | What you tend to get |
|---|---|---|
| Entry | around £850 | Light tube, clip-fixed panels, vents often extra |
| Mid | around £1,090 | 6mm twin-wall, double doors, two vents, multi-year PC warranty |
| Specialist | from £2,960 | Frame engineered for exposed, high-wind sites, delivery extra |
Footprints cluster predictably. Widths sit around 2.6m to 3m, lengths step through 2m, 4m, 6m, 8m, 10m and 12m, and ridge height runs about 2.1m to 2.5m. If you are unsure which length suits your plot and your crops, our guide on what size greenhouse you need works just as well for tunnels.
The advice above applies whatever greenhouse or tunnel you buy. If the rigid "polycarbonate polytunnel" idea is what you are after, our SteelRoot galvanised steel arch greenhouse is the direct answer to it: a closed 40x20mm rectangular hollow section galvanised steel arch, screw-fixed twin-wall polycarbonate, arches at 0.67m centres for rigidity, and ground anchors as standard. It starts from £1,199, ships free to the UK mainland and typically arrives within one to two weeks. No pressure to choose it. We would hand you the same checklist for any tunnel.
Who a polycarbonate polytunnel suits, and who should keep film
Choose rigid twin-wall polycarbonate if you want a structure that stays up year-round, looks settled in the garden, holds a little more warmth for an extended season, and never needs re-skinning. A tunnel of either kind commonly adds about four to six weeks at each end of the growing season, so the rigid version gives you that benefit without the annual cover worry. It suits a gardener on a normal or mildly exposed site who values longevity over the lowest sticker price.
Keep a film polytunnel if your priority is covering the largest area for the least money, you are happy maintaining and replacing the cover, and appearance is not a concern. Film remains the cost-effective route for big seasonal growing under cover, exactly as the RHS frames it.
One more comparison is worth making before you commit. A rigid polycarbonate tunnel and a polycarbonate greenhouse are close cousins, and the choice often comes down to footprint and budget rather than glazing. Our polycarbonate versus glass greenhouse comparison covers the glazing side in detail, so you can match the panel to the plants you grow.
A short pre-purchase checklist
Before you pay, read the listing for five things and write down the answer to each one.
- Panels screw-fixed or button-fixed, not held by spring clips.
- Closed steel section quoted with both dimensions, such as 40x20mm.
- Arch spacing stated, with closer centres preferred on a windy plot.
- Ground anchors included in the box, base brackets offered.
- Ventilation that reaches roughly 20 per cent of floor area, with the cost of any extra vents added in.
Score a tunnel against those five points and the £850 and the £1,090 options stop looking like the same thing. Spend twenty minutes on the spec sheet, add the vents you actually need to the price, and you will buy a polycarbonate polytunnel that is still standing, and still glazed, four winters from now.
Growing on an allotment? Check the site rules first: see polytunnels on allotments for what is usually allowed and what passes instead.
