SteelRoot Plot 3.14m Polycarbonate Greenhouse
A galvanised-steel arch greenhouse, 3.00 m on the ground and 3.14 m at its widest, with screw-fixed twin-wall polycarbonate.
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A galvanised-steel arch greenhouse, 3.00 m on the ground and 3.14 m at its widest, with screw-fixed twin-wall polycarbonate.
01Width
02Ridge height
03Length
04Glazing
4 mm is the base specification; choose 6 mm for extra stiffness and warmth.
05Arch spacing
1.0 m is the standard spacing; choose 0.67 m for more exposed plots.
06Add-ons optional
SteelRoot Plot 3.14 Galvanised Steel Arch Greenhouse, Twin-Wall Polycarbonate, Walk-In
A galvanised-steel arch greenhouse, 3.00 m on the ground and 3.14 m at its widest, with screw-fixed twin-wall polycarbonate.
Your build
A galvanised-steel arch greenhouse, 3.00 m on the ground and 3.14 m at its widest, with screw-fixed twin-wall polycarbonate.
Structure
Included · already in the price
Waldenhaus SteelRoot
Open the box before you buy it.
1 of 4 · Your build
What comes on the pallet, and what you arrange yourself.
Five things you arrange yourself.
2 of 4 · Base & fixings · SteelRoot
Plan the base for your selected greenhouse. Check the frame footprint and base size before preparing your site.
Peg the outer line and check both diagonals.
Most common mistake first. Tap one for why, with photos.
Whichever you pick, keep one level line all round, the door end included.
No foundation needed. The greenhouse stands on firm, level soil, held down by the ground anchors in the kit.
A base is optional. Build one for a firmer, more permanent footing: gravel, slabs, a concrete strip, sleepers or a level platform on a slope.
Our real Plot 3.14, photographed at a show. The base and the garden in each picture are illustrations.
How it stands on soil
Which fixing goes with which base.
Ask us about your plot Windy, wet or sloping? Send your postcode and a photo. We publish no anchor depths or wind ratings: none have been tested.
3 of 4 · Assembly
The frame arrives pre-drilled and bolts together. You cut only the two end walls. Read the free manual first.
Nine photographs from real builds of this greenhouse. Tap any of them.
Real builds. We tidied the backgrounds; the greenhouse is exactly as photographed. Bricks, boards and beds belong to the owners.
Glazing for your build
The build start to finish, the parts at the factory, and the crash test on the frame and the door.
Open the assembly manual Watch the assembly Ask about assembly We don't fit greenhouses; any local handyman can work from it. Ask us anything; a person answers.
4 of 4 · Parts & warranty
Three things that can go wrong, and what happens next.
Delivery
Delivery to the UK mainland is included in the price. A few places carry a surcharge because the pallet network charges us for them. Check yours before you order: the figure shown is the one checkout uses.
Catalogue I · Components
Twelve cards, every spec, no marketing puff. Click any card to open the file.
01
You choose the arch spacing at checkout. SteelRoot's base specification uses 1 m arch spacing. The optional 0.67 m close-arch layout adds more support ribs along the length for more exposed plots.
Shorter spans reduce polycarbonate panel deflection and reduce frame racking under lateral wind load. Stand inside a SteelRoot at 0.67 m and count the ribs over your head. That is the engineering you can see.
02
The 1 m spacing is the standard base specification. The optional 0.67 m close-arch layout adds more arch-to-panel fixing lines and shortens unsupported panel spans.
Wind and snow performance cannot be reduced to one headline number. Site exposure, soil or base type, anchoring and the selected configuration all matter. For coastal, upland or otherwise exposed plots, send us the postcode and site photographs before ordering.
03
Included with every SteelRoot. Each ground anchor is a bent steel tube: it slides into the foot of an arch leg, is held with one screw and is dug into the soil. That is how the greenhouse is designed to stand on firm, level ground: no concrete, no bolts, nothing else to buy. The box holds 6 / 8 / 10 / 12 / 14 anchors for 4 / 6 / 8 / 10 / 12 m at 1.00 m arch spacing and 8 / 10 / 12 / 14 / 16 at 0.67 m; the manual shows where each one goes.
On concrete, paving or timber the ground anchors do not apply. The legs are open 40 × 20 mm tubes with no base plate, so each leg drops into a bolt-down U-bracket (a post support to suit the 40 mm tube): bolt the bracket to the concrete or coach-screw it to the timber, drop the leg in, one bolt through both sides. Not included; any builders' merchant sells them. The factory gives no fixing pattern; our rule is one bracket under every leg. Loose, made-up or waterlogged ground: send us a photo before ordering. Anchoring is a condition of the structural warranty.
04
Entry-tier aluminium greenhouses tend to lose panels in moderate UK wind because of their spring-clip glazing. Those clips can corrode, lose tension, and release.
SteelRoot panels are screwed straight into the steel frame with self-drilling roofing screws and washers, one at every panel edge. The optional 0.67 m close-arch spacing reduces the panel flex that loosens fixings over time. With no spring clips, there's no spring-clip failure mode.
05
40 × 20 mm closed rectangular hollow section, galvanised steel with ZAM coating (zinc-aluminium-magnesium). The closed tube resists twist as well as bend, where an open profile flexes more readily under lateral load because it cannot resist torsion in the same way.
Every frame hole is pre-drilled for bolt assembly. Inspect fixings and any damaged coating during routine maintenance rather than drilling new holes after installation.
06
You choose the thickness at checkout. 4 mm is the base specification: lowest cost and lightest, with enough light transmission for a full crop.
6 mm is the upgrade option: stiffer between supports, more impact-resistant and warmer. Both are UV-stabilised and screwed to the steel at every edge with self-drilling roofing screws and washers. Choose 6 mm when extra stiffness or thermal retention matters more than the lowest entry price.
07
Two adults and a dry weekend. The frame is pre-drilled in a jig and bolts together; the panels and brackets go on with self-drilling screws, which cut their own hole, and nothing is welded. Tools: a cordless drill, a spanner, a spirit level, a sharp knife and a spade for the anchors. If you can put up flat-pack furniture and read a drawing, you can build this.
The one job that takes care is the glazing on the two end walls: the polycarbonate comes as full 2.1 × 6 m sheets, the roof strips go on whole, and you mark and cut the end walls from the frame itself. Read the manual before the pallet arrives and lay the bundles out against the packing list before the first bolt.
08
Five lengths from 4 m (12.0 m²) to 12 m (36.0 m²). The 3.00 m width on the ground (3.14 m at the widest point of the arch) gives you two full growing rows plus a working path, equivalent to a small allotment plot in your own back garden.
2.02 m at the convex ridge, so you stand fully upright down the centre aisle. For three growing rows plus walkways, see the SteelRoot 4 m line (16.0–48.0 m²).
09
Wax-cylinder roof auto-vents are an optional add-on, not part of the base greenhouse. Each opener pushes its vent open from around +18 °C and is fully closed by around +12 °C, so the greenhouse ventilates itself while you are away. No power, no battery, no manual handle.
Choose the number that suits your site on this page, £99 each, up to one vent per 2 m of length (two on the 4 m build, six on the 12 m). The base SteelRoot already opens front and back: both gable doors have an opening upper section for cross-flow.
Changed your mind after paying? If your order hasn't left the factory we add a vent to it: it travels on the same pallet, so there is no second delivery to pay for. Reply to your order email and we send a payment link for the £99.
10
Every SteelRoot ships with an opening window in each gable door, two per greenhouse. Both stable doors have an upper section that swings open on its own hinge.
That adds intake for the prevailing wind and gives cross-flow through the length of the structure, rather than only venting up and out at the apex.
11
The assembly manual identifies the components used in the selected SteelRoot greenhouse.
If you need a replacement, contact us with your order number, the component code and a photograph. Availability, price and despatch timing are confirmed for each request.
12
Two adults and a dry weekend. The frame is pre-drilled in a jig and bolts together; the panels and brackets go on with self-drilling screws, which cut their own hole, and nothing is welded. Tools: a cordless drill, a spanner, a spirit level, a sharp knife and a spade for the anchors. If you can put up flat-pack furniture and read a drawing, you can build this.
The one job that takes care is the glazing on the two end walls: the polycarbonate comes as full 2.1 × 6 m sheets, the roof strips go on whole, and you mark and cut the end walls from the frame itself. Read the manual before the pallet arrives and lay the bundles out against the packing list before the first bolt.
In situ · real installs
1 / 7
Why we engineer it this way
SteelRoot beside the two things it is usually compared with (an entry-tier aluminium greenhouse and a polythene tunnel) and why we built it this way for British weather.
Typical category specs; a particular brand may do better, so compare it against the product you are looking at.
Real videos
Pick the length,
not the compromise.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
The steel, the spacing and the warranty.
The steel
40 × 20mm
0.7 mm wall with ZAM coating (zinc-aluminium-magnesium). Pre-drilled, so you only bolt it.
Arch spacing
1.00 / 0.67m
0.67 m puts 50% more arches along the length, for a more exposed plot.
Frame warranty
10years
2-year manufacturing defect warranty on cellular polycarbonate panels + 10-year anti-corrosion warranty on the galvanised steel frame. Full terms
The build
DETAIL · FRAME COATINGWhere rust starts
SteelRoot uses galvanised steel with ZAM coating (zinc-aluminium-magnesium) for corrosion protection. The exact coating chemistry is published in the product specification.
Every frame hole is pre-drilled. Inspect fixings and any damaged coating during routine maintenance rather than drilling new holes after installation.
DETAIL · WAX-CYLINDER OPENERWhen it gets hot
Each optional roof auto-vent is supplied with a sealed brass tube of paraffin wax. At +18 °C the wax expands and pushes the vent open. As the air cools, the wax contracts and the vent closes itself.
It runs on no power, no batteries and no phone app. It comes fitted at the factory, so there's no opener to assemble on the day.
Optional wax-cylinder auto-opener · opens +18 °C, closes as it cools · supplied factory-assembled
DETAIL · PRE-DRILLED ARCH × BOLTWhere install starts
Marking and drilling a frame on site is where amateur kits go wrong: the gap doesn't match, the panel won't seat, and an afternoon turns frustrating.
Every SteelRoot frame is pre-drilled in a fixed jig, with tolerances to a millimetre. You bolt the frame through those holes; the panels and brackets go on with self-drilling screws, which cut their own hole where the manual shows. Panels fit on first assembly.
Factory pre-drilled frame · jig-controlled tolerance · self-drilling screws for the panels
Warranty and parts
2-year manufacturing defect warranty on cellular polycarbonate panels + 10-year anti-corrosion warranty on the galvanised steel frame.
Every part is documented, coded and held for ten years from purchase. Email us a part code or a photo and we'll source the matching part.
Not sure which length?
Find your size in 60 seconds.
Tell us how you'll use it, and we'll match you to the right SteelRoot length with the spec rationale and total cost.
No greenhouse is guaranteed against every weather event. Site exposure, base type, anchoring, glazing and arch spacing all affect performance. Contact us before ordering for a coastal, upland or otherwise exposed plot.
The product warranty is: 2-year manufacturing defect warranty on cellular polycarbonate panels + 10-year anti-corrosion warranty on the galvanised steel frame. See the full warranty terms before ordering.
1.0 m is the standard arch spacing. The 0.67 m close-arch option adds more frame-to-panel intersections along the length, so unsupported polycarbonate spans are shorter and panel movement is reduced.
Choose 1.0 m for the base specification, or 0.67 m when your site is more exposed or you want the shorter-span build. Correct anchoring and ground conditions still matter in either configuration.
Two adults and a dry weekend. The frame is pre-drilled in a jig and bolts together; the panels and brackets go on with self-drilling screws, which cut their own hole, and nothing is welded. Tools: a cordless drill, a spanner, a spirit level, a sharp knife and a spade for the anchors. If you can put up flat-pack furniture and read a drawing, you can build this.
The one job that takes care is the glazing on the two end walls: the polycarbonate comes as full 2.1 × 6 m sheets, the roof strips go on whole, and you mark and cut the end walls from the frame itself. Read the manual before the pallet arrives and lay the bundles out against the packing list before the first bolt.
We don't offer an assembly service. If you'd rather not build it yourself, any local handyman or fencing contractor can: send them the manual.
Yes: the two end walls. The roof sheets go on whole. Offer a sheet up to the end frame, mark the arch line from the frame itself, cut with a sharp knife or a fine-tooth jigsaw, leave at least 50 mm overhang past the arch, and fit it UV side (printed film) out. Measure twice: we cannot post a single replacement sheet, though any UK plastics supplier stocks the same clear twin-wall polycarbonate and we will check your sizes against the kit drawing.
Included. Each ground anchor is a bent steel tube: it slides into the foot of an arch leg, is held with one screw and is dug into the soil. That is how the greenhouse is designed to stand on firm, level ground: no concrete, no bolts, nothing else to buy. The box holds 6 / 8 / 10 / 12 / 14 anchors for 4 / 6 / 8 / 10 / 12 m at 1.00 m arch spacing and 8 / 10 / 12 / 14 / 16 at 0.67 m; the manual shows where each one goes.
On concrete, paving or timber the ground anchors do not apply. The legs are open 40 × 20 mm tubes with no base plate, so each leg drops into a bolt-down U-bracket (a post support to suit the 40 mm tube): bolt the bracket to the concrete or coach-screw it to the timber, drop the leg in, one bolt through both sides. Not included; any builders' merchant sells them. The factory gives no fixing pattern; our rule is one bracket under every leg. Loose, made-up or waterlogged ground: send us a photo before ordering. Anchoring is a condition of the structural warranty.
The frame specification is 40 × 20 mm rectangular hollow-section galvanised steel with ZAM coating.
The product warranty is: 2-year manufacturing defect warranty on cellular polycarbonate panels + 10-year anti-corrosion warranty on the galvanised steel frame. See the full warranty terms before ordering.
Both are offered, and you pick at checkout. 4 mm is the base specification: lowest cost, lightest, and it grows a full crop. 6 mm has larger cellular flutes and thicker walls than 4 mm, so it is stiffer between supports, retains more heat, and gives more body against hail and falling debris. It also flexes less than the 4 mm panel.
Choose 4 mm if you want the lowest entry price. Choose 6 mm when extra stiffness, impact resistance or thermal retention matters more than the lowest price.
Cross-ventilation is standard on every SteelRoot: both gable doors are two-part stable doors, and the upper section opens independently as a cross-flow door window, giving two opening points on every model. Wax-cylinder roof auto-vents are an optional add-on (£99 each) that open around 18°C and close around 12°C on their own. We work on one vent per 2 m of length, spaced evenly along the ridge.
Changed your mind after paying? If your order hasn't left the factory we add a vent to it: same pallet, no second delivery. Reply to your order email and we send a payment link for the £99.
For Cornish or Mediterranean-style heat exposure, side-louvre or gable-vent kits are a planned accessory. If your site is south-facing and bakes from June to September, a roll-down shading kit (sold separately) covers the gap.
SteelRoot Plot 3.14 floor areas (3.00 m on the ground times the length) in real growing language:
4 m / 12.0 m²: two full-size raised beds plus a working path; quarter-allotment scale.
6 m / 18.0 m²: three raised beds, year-round salad and tomato programme.
8 m / 24.0 m²: small-allotment scale; tomatoes, beans, cucumbers and brassicas under one roof. The most-ordered SteelRoot length.
10 m / 30.0 m²: serious-grower volume with overwintering capacity.
12 m / 36.0 m²: commercial-domestic scale; cut-flower microbusiness viable.
If you're between two lengths, take the longer one. The £150–£200 step is small money compared with rebuilding 18 months in.
Planning requirements depend on the property, location and siting. Height alone does not determine whether permission is required.
Check current Planning Portal guidance and contact your local planning authority before installation if the property is listed, in a conservation area or subject to additional restrictions.
Free delivery to most UK mainland postcodes. Any postcode surcharge is calculated from the delivery postcode and shown before checkout.
Isle of Wight £49 · Scottish Highlands £79 · Northern Ireland £99 · Scottish Islands and Isle of Man £149. Channel Islands, Isles of Scilly and BFPO are not served.
Delivered in 1–4 weeks from order, kerbside, by a tail-lift vehicle. Contact us before ordering if access is restricted.
You have 14 days from delivery to return it unused, unassembled and in the original packaging. You arrange and pay for the return pallet courier, typically £150-£250 on the mainland; we can quote a carrier rate on request. Full terms in our refund policy.
If the structure has been built and you're stuck on something specific (a wrong size, a delivery damage that surfaced during the build, a missing part), talk to us first. Most problems sort out short of a full return.
We hold replacement parts for ten years from purchase. Email us your model and length, the part code from the manual, a photo and your order number. We send an arch segment, a crossbar, fixings or a door catch at cost plus carriage, and we confirm the price and the date before you pay.
One exception, said up front: we cannot send a single polycarbonate sheet: it ships from our European workshop on its own pallet and the carriage costs more than the sheet. Clear 4 or 6 mm twin-wall is a stock item at any UK plastics supplier; send us the sizes and we check them against the kit drawing.
If provider-backed finance is available for your order, it will be shown at checkout by the payment provider before you commit.
We don't show monthly estimates on this page, because the final offer depends on provider approval and the build you choose.
Film polytunnels usually have a lower upfront price, while SteelRoot uses a galvanised steel frame and screw-fixed twin-wall polycarbonate. Compare the full specification, installation requirements, maintenance and replacement parts for your site.
SteelRoot is the rigid-panel option; a film polytunnel may remain the better choice when the lowest initial cost is the priority.
Entry-tier aluminium greenhouses and SteelRoot serve different requirements. Compare the published frame profile, panel-fixing method, anchoring, glazing options and warranty terms rather than the starting price alone.
SteelRoot uses 40 × 20 mm closed RHS galvanised steel, screw-fixed twin-wall polycarbonate and included ground anchors. The base specification uses 4 mm glazing and 1 m arch spacing; 6 mm and 0.67 m close-arch options are available.
Real engineering numbers, UK planning rules and honest comparison guides. Pick any topic that helps you decide.
SteelRoot is the Waldenhaus galvanised steel arch greenhouse for growers who want a larger, practical structure without a film-cover replacement cycle. The frame uses 40 × 20 mm RHS galvanised steel with ZAM coating (zinc-aluminium-magnesium), screw-fixed twin-wall polycarbonate and a modular arched form for serious growing space.
To compare lengths and options, see the SteelRoot range. Weighing up a polytunnel? Read our polytunnel vs polycarbonate greenhouse guide.
