The best polycarbonate greenhouses for UK gardens

What separates a good kit from a poor one

Beyond size and price, five things are worth checking on any polycarbonate kit:

1. Wall panels, not just the roof. Some kits pair a 4mm twin-wall roof with 0.7mm clear single-sheet walls. Gardensite lists the Palram Hybrid and Balance that way. Others, such as the Palram Mythos, use 4mm twin-wall on every face.
2. Panel thickness. eRoofing's thickness guide suggests 4mm twin-wall for casual growing and smaller greenhouses, 6mm as a balance of durability and cost, and 10mm for year-round growing. Its supplier table gives 6mm twin-wall a U-value of 3.5 and 10mm a U-value of 3.0, both letting through about 81% of visible light (a lower U-value means less heat lost).
3. How the panels are held in. Greenhouse Stores lists the Vitavia Venus with its panels secured by glazing bar capping rather than glazing clips, and says this keeps the glazing fully secure. One forum poster explained that a panel bows in wind and its edges lose contact with the frame; another found the panels held by the kit's plastic glazing strips were mostly the ones that blew out, while those fixed with ordinary glazing clips, four per side, fared better.
4. A stated wind and snow rating, plus anchoring. Gardensite lists Palram's figures (56mph and 75kg/m² for its Mythos, Hybrid and Balance; 62mph and 100kg/m² for the Glory). The Vitavia pages we checked give no rating. Greenhouse Stores' point is worth remembering: "A thicker sheet does not make poor anchoring safe."
5. UV protection on the right side. Greenhouse Stores says the UV-protected face of twin-wall sheet must point outwards, and that fitting it backwards can make it degrade sooner.

If you are still deciding between materials, our polycarbonate vs glass comparison covers light, heat and safety. This guide assumes you have chosen polycarbonate.

Six polycarbonate greenhouses compared

Specs are from UK retailer pages checked on 25 and 27 October 2026: Gardensite for the Palram models and the Neptune, Greenhouse Stores for the Venus. Sizes are width x depth.

Price ranges run from the retailer's sale price to its listed full price, before delivery and extras.

Which thickness for your site

• Sheltered town garden, unheated, spring to autumn use: 4mm twin-wall is enough. Prefer twin-wall walls as well as roof (Mythos, Venus, Neptune).
• Open, exposed or coastal plot: anchoring and fixing matter as much as thickness. Choose a kit with a stated wind rating or capping strips, fix it to a solid base, and buy the anchor kit if one is offered. Gardensite suggests Palram's £64.99 anchoring kit if bad weather is forecast.
• Heated over winter: go thicker; eRoofing suggests 10mm for year-round growing. The Glory's 10mm twin-wall is by far the thickest here. Our greenhouse heater comparison works out what heating a 6x8 glass greenhouse costs.

0.7mm clear walls are see-through, but they are single sheets. Greenhouse Stores notes that twin-wall panels trap air and normally lose heat more slowly than a clear single sheet, and that twin-wall sheet is more rigid than a thin single one.

What owners complain about, and what to do

We read owner threads on the growfruitandveg.co.uk forum and the retailer reviews to see where polycarbonate greenhouses go wrong.

Panels blowing out. It came up in all four threads we read. In one thread an owner lost about half their panels in a storm; in another, an owner's B&Q 6x6, bought four years earlier, lost most of its sheets in its first winter gales, and they blew out again after being glued back with a construction adhesive. One poster explained that polycarbonate bows into an aerofoil shape in wind, so the edges lose contact with the frame. Gardensite carries a Hybrid review from an owner whose greenhouse collapsed in an 80mph wind on an exposed Dartmoor slope, well above its 56mph rating; the reviewer later reinforced it with angle iron and steel cable. What helps:

• Anchor the base properly before glazing (see our greenhouse base guide).
• One poster advised three or four blobs of silicone on each side of the pane; another recommended Dow Corning 794 glazing silicone rather than ordinary silicone. Another taped the panels as a quick fix, but found the tape let rain under.
• On an exposed site, look for capping strips or a published wind rating before you buy.

Panels yellowing and going brittle. A BillyOh owner's south-facing roof panels crumbled after about four years. Another poster pointed out that only one face is UV-protected, and the owner admitted the panels had been refitted without checking which way round.

Fiddly assembly and flimsy feel. One owner found a budget 6x8 frame "quite flimsy but ok once bolted together" and its plastic glazing strips "very difficult to install". One Gardensite reviewer called the Mythos "a little fiddly" to build.

Condensation inside the panels. One owner found condensation inside the flutes of twin-wall panels. Greenhouse Stores says twin-wall sheet needs the correct end treatment, closing the channels as the maker directs to keep out dirt, insects and moisture, so do not skip the end strips in the kit.

How we chose

We have not seen these greenhouses in person. We compared the specifications on UK retailer pages checked on 25 and 27 October 2026 and read owner forum threads and retailer reviews, then picked one kit for each need, from budget 6x8s to a heated 8x8. No pick has an affiliate link, and none was chosen for one.

Cleaning and replacing panels

The Plastic Sheets Shop advises washing polycarbonate once or twice a year with lukewarm water, a little washing-up liquid and a soft microfibre cloth, rinsing the cloth often. It warns against scouring pads, pressure washers and solvents such as thinners, benzene or acetone, which soften the plastic and leave a haze.

To replace a cracked or lost panel, measure the old one and buy the same thickness: Greenhouse Stores says to use a thickness approved for that frame. Fit it UV side out.

Which should you choose?

• Lowest cost with twin-wall all round: Palram Canopia Mythos 6x8.
• Clearer walls on a budget, sheltered garden: Palram Canopia Hybrid 6x8.
• Panels held by capping strips, longest frame warranty: Vitavia Venus 5000 8x6.
• 8x8 with two roof vents: Vitavia Neptune 6700 8x8.
• Wide doors and a low ramp for easy access: Palram Canopia Balance 8x8.
• Heated, year-round growing: Palram Canopia Glory 8x8.

Short of wall space instead of ground? See our lean-to greenhouse picks, or browse all our greenhouse buying guides.

Related: Polycarbonate vs glass greenhouses: which is better for a UK garden?

Questions people ask

Is polycarbonate good for a greenhouse?

Yes, if it is twin-wall and well fixed. Twin-wall panels trap air and lose heat more slowly than a single sheet, and Gardensite describes Palram's panels as virtually unbreakable. The weak points are panels blowing out in storms and UV damage if sheets are fitted the wrong way round. See our polycarbonate vs glass comparison for the full trade-off.

Is 4mm, 6mm or 10mm polycarbonate best for a greenhouse?

4mm twin-wall is fine for an unheated greenhouse used from spring to autumn. 6mm is a middle ground on durability and cost, and 10mm suits a greenhouse you heat through winter: one supplier table gives 6mm a U-value of 3.5 and 10mm 3.0, with similar light transmission of about 81%. On an exposed site, anchoring and fixings matter as much as thickness.

How do you stop polycarbonate greenhouse panels blowing out?

Anchor the base to a solid foundation first. Forum owners suggest three or four blobs of silicone on each side of the pane (one recommends a glazing silicone such as Dow Corning 794), and one owner who sealed panels all round with clear mastic stopped losing them (tape is a stopgap: one owner found rain got under it), and some kits use capping strips rather than clips to hold the panels. Choose a kit with a stated wind rating for an exposed plot.

How do you clean polycarbonate greenhouse panels?

Lukewarm water with a little washing-up liquid and a soft microfibre cloth, once or twice a year. Do not use scouring pads, a pressure washer or solvents such as thinners or acetone, which soften the surface and leave a haze.

Can you replace polycarbonate greenhouse panels?

Yes. Measure the old panel, buy the same thickness approved for that frame, and fit it with the UV-protected face outwards. Sheets fitted the wrong way round can degrade sooner; one forum owner's refitted roof panels turned brittle after about four years.

Sources

1. Palram Canopia Mythos 6 x 8 ft Greenhouse, Gardensite
2. Palram Canopia Hybrid 6 x 8 ft Greenhouse, Gardensite
3. Palram Canopia Balance 8 x 8 ft Green Greenhouse, Gardensite
4. Palram Canopia Glory 8 x 8 ft Premium Greenhouse, Gardensite
5. Vitavia Neptune 6700 8 x 8 ft Greenhouse, Gardensite
6. Vitavia 8x8 Neptune 6700 Greenhouse, Polycarbonate Glazing, Greenhouse Stores
7. Vitavia 8x6 Venus 5000 Greenhouse, Polycarbonate Glazing, Greenhouse Stores
8. Twin-wall vs single-wall polycarbonate greenhouses, Greenhouse Stores
9. Guide to polycarbonate sheet thickness for greenhouses, eRoofing
10. Cleaning polycarbonate sheets, The Plastic Sheets Shop
11. Polycarbonate (thread 80555), growfruitandveg.co.uk forum
12. My polycarbonate keeps blowing out, growfruitandveg.co.uk forum
13. Polycarbonate greenhouse, growfruitandveg.co.uk forum
14. BillyOh polycarbonate roof panels have degraded after only 4 years, growfruitandveg.co.uk forum