Aluminium greenhouse buying guide

Aluminium is the default UK greenhouse for good reason: it never rots, never needs painting, and puts more of your budget into growing space than any other frame. The catch is that "aluminium greenhouse" covers everything from a £150 flimsy to a £2,000 lifetime structure — and the differences hide in the specification, not the photos.

The frame: gauge and bracing, not just the metal

All aluminium resists rust; not all frames resist wind. Heavier box-section extrusions and diagonal bracing are what keep a greenhouse rigid when gusts load the glazing. Listings rarely quote gauge directly, so use the proxies: frame weight, stated wind ratings, and whether the glazing is held by bar capping (better) or spring clips alone.

Powder-coated or mill (silver) finish? Structurally identical — coating adds colour and a small premium. Mill finish weathers to a dull grey and lasts just as long.

Glazing decides the price — and the experience

• Horticultural glass — cheapest, clearest, replaceable pane by pane; shatters into shards, so think twice with children around.
• Toughened glass — the safety upgrade; crumbles like a car windscreen instead of shattering. Worth it for family gardens and larger panes.
• Twin-wall polycarbonate — near-unbreakable, insulates roughly twice as well as single glass and diffuses light (fewer scorched seedlings), at the cost of clarity and some wind-suck vulnerability if poorly fixed.

The base is guarantee-critical

Most aluminium greenhouses are designed for a matching perimeter base kit — often sold separately, so check whether the listing includes it before comparing prices. The base needs to sit level on slabs or concrete: an uneven base twists the frame, cracks glazing and stops doors running. It's the most common assembly mistake, and skipping it usually voids the guarantee.

Anchor it — aluminium is light

The frame that makes delivery cheap also makes an unanchored greenhouse a kite. Bolt the base down, and glaze on a calm day. If your garden is exposed, prioritise bar-capped glazing and check the stated wind rating.

Ventilation: the spec line everyone skips

Aim for at least one roof vent per 6ft of length, ideally with an inexpensive automatic opener (they need no power — a wax cylinder does the work). Louvre side vents add through-flow. Under-ventilated greenhouses cook seedlings in April sunshine faster than frost ever kills them.

Compare before you buy

The same manufacturer's aluminium greenhouse frequently appears at several retailers at different prices — exactly what we track, with price history so a "sale" price can be checked against what it actually sold for: