The Greenhouse Buying Guide
Everything worth knowing before you spend a few thousand dollars on a structure you intend to keep for a decade. No brand names, no sales pitch - just the decisions that actually matter, in the order you need to make them.
1. Choosing a size
Size is the decision people most often get wrong, and it is the one that cannot be undone later. The common regret is buying too small.
A greenhouse fills faster than expected. Seed trays in spring, potted stock in summer, overwintering tender plants in autumn, plus benches, a potting area, watering cans, bags of mix, and a walkway you can actually turn around in. Growing space is not the same as floor space.
| Footprint | Roughly | Realistically suits |
|---|---|---|
| 6×8 – 7×8 ft | 48–56 sq ft | Seed starting and a small overwintering collection. One person, one bench, tight turns. |
| 8×12 – 9×12 ft | 96–108 sq ft | The most common sweet spot. Benches down both sides, a center aisle, room to grow through the season. |
| 9×16 – 10×16 ft | 144–160 sq ft | Year-round growing with space for tall crops, a potting station, and storage. |
| 12×20 ft and up | 240+ sq ft | Serious production, market growing, or a small commercial operation. |
Work out the size you think you need, then look at the next size up. The cost difference between an 8×10 and an 8×12 is usually modest. The cost of replacing a greenhouse that turned out too small is the whole greenhouse.
2. Where to put it
Before you choose a model, walk the actual spot. Five things matter, roughly in this order:
- Sun. Aim for six or more hours of direct winter sun. Winter is the constraint, not summer — the sun sits lower and shadows run far longer. Check the site in the season you most want to be growing.
- Orientation. In the northern hemisphere, running the ridge east–west gives the broadest south-facing surface and the most even winter light. North–south is often better for summer-dominant growing. If you can only have one, favor winter.
- Drainage. Never site on ground that pools. Standing water rots benches, undermines foundations, and turns the floor into a permanent mud pit.
- Wind exposure. Open, exposed sites take far more load. A hedge or fence upwind helps enormously, but do not place a solid wall so close it creates turbulence.
- Access. You will carry bags of mix, trays, and water to this building constantly. Also consider whether power and a water line can reach it, and — critically — whether a freight pallet can get near the site on delivery day.
3. Foundations and base prep
Almost every greenhouse needs a level, square base prepared before the kit arrives. This is the step people underestimate, and it is the most common cause of a stalled build.
Common approaches, cheapest to most permanent:
- Compacted gravel over a leveled bed — drains well, forgiving, the usual choice for hobby builds.
- Timber or manufacturer base kit on leveled ground — gives a clean anchor point for the frame.
- Concrete perimeter footing — the most permanent, often required for larger structures or where a permit demands it.
- Full concrete slab — easiest to keep clean, but the hardest surface to drain and the least forgiving of error.
Whatever you choose, it must be level and diagonally square. A base out of square by even an inch or two makes panels bind and doors sit crooked, and no amount of force during assembly will correct it.
4. Glazing: polycarbonate, glass, polyethylene
Glazing is what you see through and what holds the heat. The three common materials behave quite differently.
Twin-wall polycarbonate
The most common choice, sold by thickness in millimeters. Thickness drives insulation and strength:
- 4mm — light, economical, fine for season extension in mild climates.
- 6mm — the practical middle. Noticeably better heat retention and rigidity.
- 8–10mm — strongest and warmest, best for cold winters, heavy snow, and true year-round growing.
Polycarbonate diffuses light rather than transmitting it clear, which is usually an advantage: it scatters light around the plant instead of scorching one side. Look for a UV-protective coating on the exterior face — without it, panels yellow and turn brittle within a few years.
Glass
The clearest view and the most traditional appearance. Toughened or tempered safety glass is the sensible specification. Glass is heavier, needs a more substantial frame and foundation, costs more, and can break — but it does not yellow, and a glass house looks like a permanent piece of architecture rather than a kit.
Twin-wall polyethylene
Flexible, excellent light diffusion, strong insulation for the price, and very hard to break. It is not as clear as glass or polycarbonate, so it suits growers who care more about plant performance than about the view.
5. Frame material
The frame is the one component you cannot replace. Glazing can be swapped; a corroded frame means a new greenhouse.
Aluminum does not rust. It forms a stable oxide layer and stops there. Powder-coated or galvanized steel relies entirely on its coating, and every drilled hole, cut edge, and scratched fastener point is a place that coating has been broken. In a humid greenhouse — which is the entire point of a greenhouse — those points are where corrosion starts.
Steel frames are stiffer for the money and are the right answer for some commercial spans. But for a structure you intend to keep for a decade or more in a permanently damp environment, extruded aluminum is the lower-risk choice.
Wood — typically cedar or redwood — is the third option. It is naturally rot-resistant, insulates better than metal, and looks superb. It also requires periodic maintenance that aluminum does not.
6. Snow load, wind, and your climate
Two numbers decide whether a greenhouse survives where you live.
- Snow load, quoted in pounds per square foot. Snow is far heavier than people expect, and wet spring snow is the worst of all. If you get real winters, this figure matters more than any other specification on the page.
- Wind rating, quoted in mph. Exposed and coastal sites need a higher rating, and proper anchoring matters as much as the rating itself.
Check your local design values rather than guessing. Your county building department publishes the ground snow load and design wind speed used for permits in your area, and those are the numbers to buy against.
A greenhouse is a large, light, empty box. Unanchored, it is a sail. Nearly every greenhouse lost to wind was lost because it was never properly fixed to its base.
7. Permits, HOAs, and setbacks
Check before you buy, not after the pallet arrives. Requirements vary enormously by jurisdiction, and the answer is rarely obvious.
- Many areas exempt structures under a floor-area threshold — often around 100 to 200 sq ft, but this is entirely local.
- A permanent foundation, electrical supply, or plumbing will frequently trigger a permit even when the size alone would not.
- Setbacks dictate how close to a property line or another structure you may build.
- An HOA may have its own rules on placement, height, and appearance that are stricter than the city's.
A ten-minute call to your local building department before ordering is the cheapest insurance in this entire process.
8. Ventilation and climate control
Overheating kills more greenhouse plants than cold does. A sealed greenhouse on a clear day can exceed outside temperature dramatically, and it happens faster in spring than most people anticipate.
Plan for airflow from the start:
- Roof vents let the hottest air escape where it collects. Automatic openers driven by a wax cylinder need no power and work while you are away — the single highest-value accessory for most owners.
- Side or louvre vents draw cool air in low and create cross-flow.
- A circulation fan keeps air moving, which suppresses fungal disease as much as it moderates temperature.
- Shade cloth in high summer, particularly at lower latitudes and high-altitude desert sites where light intensity is severe.
9. Assembly: time, tools, and people
Most hobby kits are designed for owner assembly, but plan realistically.
- Budget a weekend, not an afternoon. A mid-size kit typically runs eight to sixteen hours of real work. Larger or glass models take longer.
- Two people minimum. Panels and roof sections are awkward rather than heavy, and holding while fixing is a two-person job.
- Prepare the base first. Level and square, fully finished before the kit arrives.
- Inventory every part before you start. Kits arrive with labeled hardware bags. Checking them against the manifest on day one turns a missing bracket into a phone call rather than a stalled build.
- Do not assemble in wind. Large panels and gusts are a genuine hazard, and a dropped panel is an expensive lesson.
10. How a greenhouse actually gets to you
This surprises more first-time buyers than anything else on this page. A greenhouse does not arrive by parcel courier. It arrives on a pallet, by freight carrier, and the process works differently in ways that matter.
The carrier calls to book an appointment, delivery is to the curb rather than to your chosen spot, and you are responsible for getting several hundred pounds of pallet from the roadside onto your property. Most importantly, you must inspect the shipment before signing for it — signing a clean delivery receipt is the carrier's evidence that everything arrived undamaged.
We have written this up in full, because getting it right is the difference between a smooth delivery and an expensive dispute.
Read how freight delivery works →