Should I buy an aluminium or a wooden greenhouse?

The frame is a longer-lived decision than the glazing. Aluminium is the default for good reasons, and the case for timber is largely aesthetic plus a few genuine practical advantages. Both, well founded and properly anchored, last decades.

Step by step

1. Start with the maintenance you are willing to do.Aluminium needs none for its whole life. Cedar needs oiling every two to three years to stay looking good, and softwood needs treating more often than that or it will fail at the joints.
2. Compare the light penalty.Timber frames are thicker than aluminium sections, so a wooden greenhouse of the same footprint has measurably less glass and a little less light. It is a small difference and matters most in winter.
3. Think about fitting things to it.Timber takes a screw anywhere, which makes staging, hooks, shelf brackets and string supports easy. Aluminium requires the proprietary bolts that slide into the glazing bar channel — cheap and effective, but you need to buy them.
4. Consider condensation and cold bridging.Aluminium conducts heat well, so the bars run colder than the glass and condensation forms on them first, dripping onto plants below. Timber bars are warmer. Neither is a serious problem in a well-ventilated house.
5. Check the anchoring, whichever you choose.Wind is the main destroyer of greenhouses. Both types must be bolted down to a proper base — a manufacturer's base kit, a concrete or paved perimeter, or ground anchors. This matters far more than the frame material.
6. Look at the glazing method.Aluminium uses spring clips and glazing strip, which allows a pane to be replaced in minutes. Timber usually uses beads or putty, which is slower to replace but much less prone to panes slipping.

Tips

• In a conservation area or beside a listed building, a timber greenhouse is far more likely to be acceptable if any consent is needed. Check before ordering.
• Second-hand aluminium greenhouses are common, cheap and entirely serviceable — the frame does not deteriorate. Dismantling and re-erecting one is a weekend job for two people and a set of numbered photographs.
• Whatever the frame, check the glazing bar profile before buying accessories. Different manufacturers use incompatible channel sections and the clips are not interchangeable.

Common mistakes

• Buying a cheap softwood frame and not treating it — The bottom rail and the glazing beads stay wet, and rot starts within a few years. Timber greenhouses are a maintenance commitment, not just a purchase.
• Assuming the frame material determines how warm it is — The glazing, the ventilation regime and whether the house is lined matter far more than whether the bars are metal or wood.
• Skimping on the base to afford a better frame — A greenhouse on an inadequate base racks, cracks panes and eventually fails in wind, whatever the frame is made of.

Alternatives

• Aluminium: Slim sections, no maintenance, no rot, and integral glazing bar channels that accept clips, hooks, insulation fixings and shading. Cheapest per square metre. Conducts heat readily, so it loses slightly more heat than timber and shows condensation on the bars first.
• Western red cedar: Naturally durable without preservative, attractive, holds a screw anywhere so fitting staging and hooks is trivial, and insulates better than metal. Substantially more expensive, needs oiling every few years to keep its colour, and the thicker frame members cast more shade.
• Treated softwood: The cheapest timber option and the one most often seen on budget models. Needs regular treatment, and where the timber stays wet against glazing beads it will eventually rot. Check what treatment grade is specified before buying.
• Powder-coated aluminium: Aluminium with a coloured finish, usually green, black or off-white. All the practical benefits of aluminium plus the appearance most people actually want, for a modest premium. The commonest choice in an ornamental garden.

Questions people ask