Waldenhaus SteelRoot Plot 3.14
If you are searching for a heavy-duty polytunnel, this is what we build instead: a ZAM-coated steel arch glazed with twin-wall polycarbonate. Five lengths, £899–£1,799. Ground anchors in the kit. Every price is on this page.
Engineered for British storm conditions.
Why people search for a heavy-duty polytunnel
The phrase usually stands in for three specific frustrations. Here is how the Plot 3.14 is built against each one.
The cover, not as a consumable
On a tunnel the polythene film is a consumable: you buy it, you fit it, and a few years later you buy it again. The Plot 3.14 is glazed with twin-wall cellular polycarbonate panels, screw-fixed through the steel with stainless screws and sealing washers. The panels are part of the structure rather than a wrap stretched over it.
Anchors in the kit, not a line on the invoice
Ground anchors are included — 8 on the 4 m, rising to 24 on the 12 m — driven straight into typical UK soil. There is no concrete foundation to pour and no separate anchor kit to add at checkout.
Ventilation in the doors
There is a door at each end. Open both and the house ventilates end to end. Automatic roof vents exist as a paid upgrade — the price is in the next section, not buried in a footnote.
The frame underneath all of it is 40 × 20 mm rectangular hollow section steel with a ZAM coating (zinc-aluminium-magnesium), with arches at 1.0 m as standard and a 0.67 m option.
The five lengths and what they cost
Base prices for the Plot 3.14. Width is 3.14 m on every length; only the length changes.
| Length | Footprint | Price | Per metre | Buy |
|---|---|---|---|---|
| 4 m | 3.14 × 4 m · 10 × 13 ft · 12.6 m² | £899 | £225 | Build the 4 m |
| 6 m | 3.14 × 6 m · 10 × 20 ft · 18.8 m² | £1,099 | £183 | Build the 6 m |
| 8 m | 3.14 × 8 m · 10 × 26 ft · 25.1 m² | £1,299 | £162 | Build the 8 m |
| 10 m | 3.14 × 10 m · 10 × 33 ft · 31.4 m² | £1,599 | £160 | Build the 10 m |
| 12 m | 3.14 × 12 m · 10 × 39 ft · 37.7 m² | £1,799 | £150 | Build the 12 m |
Base kit prices. Upgrades are priced separately in the next section. Shipping is calculated at checkout.
Three decisions, and what each one costs
Everything above is the base kit. There are exactly three upgrades on the Plot 3.14, and none of them is bundled in silently.
1. Glazing: 4 mm or 6 mm
4 mm twin-wall polycarbonate is standard on every length. 6 mm is a paid upgrade at +£100. The thicker panel is the one to pick if the house will be working through the colder half of the year rather than sitting idle.
2. Arch spacing: 1.0 m or 0.67 m
Arches sit at 1.0 m as standard. The closer 0.67 m spacing puts more steel into the same length and is +£50 on the 4 m and +£70 on the 6 m to 12 m. It is the option people choose for open, exposed plots.
3. Automatic roof vents
Auto-vents are +£99 each and they are paid, not included. They open on temperature without you being there, which matters on a working weekday in June. The builder caps them by length, from two on the 4 m to six on the 12 m; the doors at both ends are the standard ventilation.
What arrives on the pallet
- Frame: galvanised steel arches and rails in 40 × 20 mm rectangular hollow section, ZAM-coated (zinc-aluminium-magnesium).
- Glazing: 4 mm twin-wall cellular polycarbonate as standard, 6 mm as a paid upgrade.
- Dimensions: 3.14 m wide, 2.02 m to the ridge, in the length you choose from 4 m to 12 m.
- Doors: one at each end.
- Anchoring: ground anchors included, 8 to 24 depending on length. No concrete foundation.
- Fixings: stainless screws and sealing washers — the panels are screwed to the frame, not clipped into it.
- Arch spacing: 1.0 m as standard, 0.67 m as a paid option.
Delivery, shipping and warranty
Delivery: 1-4 weeks from order.
Shipping is calculated at checkout; some Highland, island and Northern Ireland postcodes carry a surcharge.
Warranty: 2-year manufacturing defect warranty on cellular polycarbonate panels + 10-year anti-corrosion warranty on the galvanised steel frame.
One thing that is not in the box. Polycarbonate end-sealing tape is not included in the kit. The open flutes at the top and bottom edge of each panel should be taped during assembly — aluminium tape on the top edge, breather tape on the bottom — and both are a few pounds from any UK builders' merchant or online. We would rather you knew that now than on the morning you build it.
Questions people actually ask
Is this a polytunnel?
No. It is a steel arch greenhouse: rigid twin-wall polycarbonate panels screwed to a coated steel frame, with no polythene film anywhere in the build. It answers the same job — a walk-in growing space over a long footprint — with different materials. If you want the two formats set against each other, read our polytunnel vs polycarbonate greenhouse guide.
Will it survive a bad winter?
No garden structure is. What we can tell you is how it is built and how it is anchored: 40 × 20 mm ZAM-coated steel arches at 1.0 m spacing, or 0.67 m as a paid option; rigid polycarbonate screwed through the frame with stainless fixings; and one ground anchor per metre of length, included in the kit.
Is it suitable for a windy site?
It is the shape people choose for exposed plots — a low arch with no flat gable to catch the weather, anchored along its full length. Buyers on open ground usually take the 0.67 m arch spacing as well. We do not publish wind ratings.
Do I need a concrete base?
No. The ground anchors are driven into typical UK soil — 8 on the 4 m through to 24 on the 12 m — and they come with the kit. What the structure does need is a level, well-drained rectangle, marked out and squared before you start.
What is not in the kit?
Polycarbonate end-sealing tape. Everything structural is supplied — frame, panels, doors, fixings, ground anchors — but you buy the aluminium and breather tape for the panel flutes yourself and fit it as you glaze.
How wide is it, and how tall?
3.14 m wide and 2.02 m to the ridge on every length. On the site the sizes are listed in feet as 10 × 13, 10 × 20, 10 × 26, 10 × 33 and 10 × 39 ft.
Should I choose 4 mm or 6 mm polycarbonate?
4 mm is standard and is what most people take. 6 mm is a paid upgrade at +£100 and is the one to choose if you plan to grow through the colder months rather than shut the house down in October.
Do I need the 0.67 m arch spacing?
Not on a sheltered plot. It is a paid option — +£50 on the 4 m, +£70 on the 6 m to 12 m — and it puts noticeably more steel into the same length. Open, exposed ground is the use case it exists for.
Which length suits my plot?
Measure the rectangle you can actually give it, then take a length that leaves you a working path at each end and room to walk round the outside. The 4 m at 12.6 m² is a full walk-in house; the 12 m at 37.7 m² is a serious growing space. The per-metre price falls as the house gets longer, so if you are torn between two, the longer one is the better value per metre.
What else should I compare before buying?
Everything in the same bracket, honestly — heavy-duty tunnels included. Our guide to polytunnel alternatives in the UK lays out the other routes and where each one makes sense.
Pick a length
Base prices, ground anchors included, upgrades priced on the product page.
4 m — £899 6 m — £1,099 8 m — £1,299 10 m — £1,599 12 m — £1,799