Greenhouse
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A backyard greenhouse succeeds or fails on the space you leave around it, not on the footprint of the kit. Walk the plot, write down the widest unobstructed rectangle you can find, then subtract working clearances of at least 60 cm on every side where you need to fit, clean, reach a door or manoeuvre a wheelbarrow. A structure hemmed in on all four sides is frustrating to use.
Note the ground itself. A gentle slope is workable, but anything steeper than roughly 10 percent will need levelling and may expose you to drainage problems. Identify where water collects after rain, since floors sitting in wet ground soften, tilt and encourage algae. Tree roots close to the surface are a common obstacle, and mature trees cast moving shade that changes through the year.
Mark every obstruction: sheds, air conditioning units, downpipes, gutters, fences, compost bins, play equipment and overhead utility lines. Take photographs from the house at eye level and from a corner of the plot at two metres high; they reveal sight lines that a plan drawing hides. Consider too how much noise from the house reaches the plot.
Light decides what you can grow and how well. Track the sun across your plot on a clear day in midsummer and again in midwinter, noting where shadows fall from houses, fences, garages and trees. Greenhouses in temperate climates generally need six to eight hours of direct light through the growing season, and the best results come from structures standing in full sun.
Orientation depends on hemisphere. In the northern hemisphere the equator-facing side should carry the largest glazed area, so a ridge running east to west with a south-facing glass wall gives even light. In the southern hemisphere, reverse this and glaze the north face. Lean-to structures can be built against the sun-facing wall of the house, which is efficient on a narrow plot.
Plan for shade as well as sun. In hot climates a deliberate afternoon shadow from a fence or a deciduous tree is an asset rather than a defect, because it lowers summer temperatures and reduces the load on ventilation. Large evergreen trees are harder to manage. Where a mature tree must come down, check local rules first, since protected species carry preservation orders.
Plan the route from the delivery gate to the finished base as carefully as the greenhouse itself. Most kits arrive as flat panels and lengths of frame, but glass is heavy, brittle and awkward. A van to the driveway is only the start. Measure every gate, corner and step, and check that a sack truck or trolley can carry a panel to the build site.
Water and power decide how the greenhouse will be used. Note the distance to the nearest outdoor tap, because a hose run longer than about 30 metres is awkward and slow, and adding a dedicated water point will change your routine. For electricity, a weatherproof socket on an outdoor circuit with residual current protection is needed for fans, heaters, lighting and irrigation timers.
Plan the walking distance from the house. A greenhouse used daily is worth a short walk; one at the far end of a long garden tends to be visited at weekends. Keep a path wide enough for a wheelbarrow and for carrying trays of seedlings, and make sure a hose can reach the structure without crossing beds.
Permitting depends on where you live, so check before you buy. Many jurisdictions exempt small greenhouses below a given floor area, height or distance from a boundary, while anything larger may require a permit and a site plan. Building codes often touch foundations, wind loading and glazing safety, and planning rules may limit how close a structure can sit to a property line.
Other constraints include drainage and runoff rules, restrictions over utilities, easements or rights of way, and fire service access requirements in some areas. If you are on a septic system or private well, keep the greenhouse clear of the drain field and any well head, and avoid heavy loads over buried lines.
Neighbours are part of the approval process even when no formal permission is needed. A greenhouse that changes the light reaching a neighbour's vegetable patch, blocks a path or drips condensation onto a patio will cause friction. Talk to adjacent households early, explain what you plan to build, and orient the tall side away from a shared boundary where possible.
Choose size by the plants and the people, not by the empty ground you think you have. Work out the growing area you actually need in square metres and add circulation space: single-sided staging with a 60 cm path, or staging on both sides with a 90 cm path for twin-door and multi-span layouts. Adding a hobby unit to a full-size structure later is expensive, so plan for expansion now.
| Structure size | Typical footprint | Best suited to | Practical note |
|---|---|---|---|
| Hobby unit | 2 to 6 square metres | Herbs, salad leaves | Cheap, limited floor area |
| Tunnel or polytunnel | 6 to 18 square metres | Rows of vegetables | Good value, must be anchored |
| Small multi-span | 12 to 30 square metres | Mixed crops in bays | Useful zoning, costlier frame |
| Large residential multi-span | 30 square metres and above | Continuous family supply | Needs planning, level base |
The most common mistake is buying too large. A structure you can heat, water and work comfortably beats a bigger one that stays half empty. Multi-span layouts also let you allocate one bay to propagation, one to salad and one to tall crops, which argues for a slightly larger footprint if space and budget allow.
A backyard can host very different structures, and the choice balances light capture, cost, wind resistance and how the building looks against neighbouring houses. A low-profile structure on the sun-facing wall of the house is often more acceptable to planners and neighbours than a tall freestanding glasshouse, and it borrows the wall's thermal mass.
| Style | Light capture | Wind resistance | Typical use |
|---|---|---|---|
| Hobby or mini greenhouse | Low to moderate | Low | Seedlings, chillies, hardening off |
| Lean-to | Good, one sided | Moderate | Against a wall, useful in winter |
| Gable house | Excellent | Moderate | All-round growing across the year |
| Polytunnel | Moderate to good | Low unless anchored | Row crops, quick summer production |
| Multi-span | Excellent | Good once braced | Family production and zoning |
Tunnels and polytunnels are the workhorses of a small plot because they deliver usable growing area for the least money per square metre. They are also the most exposed to wind, which makes correct anchoring part of the installation rather than an optional extra. Whatever style you choose, buy a door wide enough for a wheelbarrow, because access determines how much you harvest.
The frame carries the load and largely determines the life of the structure. Aluminium extrusions need almost no maintenance, hold their shape and cast less shadow than heavy steel because the sections are slimmer. Painted steel is stronger and usually cheaper, but it rusts at joints and needs periodic touching up. Timber frames insulate well but need regular sealing and checking for rot near the ground.
The cover decides how much light and heat reach the plants, and the options behave very differently in a domestic setting.
| Cover | Light | Heat retention | Typical life | Notes |
|---|---|---|---|---|
| Glass | Excellent | Very good | 15 to 25 years | Heaviest, glares, panes need replacing |
| Twin-wall polycarbonate | Good | Good | 10 to 15 years | Diffuse light, must be UV stabilised |
| Single-wall polycarbonate | Fair | Fair | 5 to 8 years | Condenses readily, short lived |
| Film or polytunnel sheeting | Moderate | Low | 3 to 5 years | Cheap, replaced regularly |
A practical compromise is a glass or polycarbonate roof with polycarbonate on the sides, giving good light where it matters most and impact resistance where children and pets are around. Always check that polycarbonate is UV stabilised, because unstabilised panels turn yellow and brittle within a couple of seasons. Ventilation matters as much as the cover when the sun is high.
A greenhouse is only as stable as its base. The two common domestic choices are a ground-level frame fixed with pegs and straps, and a small slab or timber base for glass houses needing a washable floor. Slab bases are durable and easy to hose down, but they are a permanent commitment and require firm, level ground to begin with.
On level soil, ground anchors are adequate provided the frame is fixed at every designated point and the anchors are driven below the depth at which the soil softens or freezes. On slopes or soft ground, a level platform of compacted hardcore with a treated timber bearer frame solves most problems. Whatever the base, keep the frame at least 10 cm above finished ground level so splashback cannot wick in.
A small greenhouse works best when every square metre has a job, so draw the layout on paper before ordering staging and mark the door swing so it never collides with a bench. Along one side place a fixed potting bench at standing height; along the other, tiered staging for crops needing maximum light. Keep a central aisle of at least 60 cm, wider if a wheelbarrow passes through.
Put the potting area at the far end near a water point, so spilled compost never blocks the path and you can fill cans without crossing the growing area. Store tools, twine, netting and spare covers in a lidded box or corner shelf rather than on the floor, where they hold damp and harbour pests. Route irrigation pipe along the base rail so it can be drained before a frost.
Group plants by water need and height, with tall crops such as tomatoes on the side that casts least shade, usually the north side in the northern hemisphere. Keep the area near the door clear for incoming seedlings and empty crates. A tidy layout with clear circulation is what makes a small structure feel productive rather than cramped.
It depends on where you live. Many authorities exempt small greenhouses below a specified floor area, height or distance from a boundary, but larger structures may need planning permission and a site plan. Check the rules for your council before ordering, and ask specifically about foundation type, wall height and glazing, since those details usually decide the question.
Allow at least 60 cm of working clearance on two sides, more where possible, so you can replace a panel or carry a wheelbarrow without dismantling anything. Leave the door end clear for access and delivery, and keep away from any fence line where a fixed cover could touch the boards.
Glass gives the best light and lasts longest, which matters most for tomatoes, peppers and winter crops. Polycarbonate is roughly half the weight, far more impact resistant and better at spreading light, so many gardeners prefer it where hail, children and pets are a factor. Single-wall polycarbonate is the least durable option and tends to fog.
Choose the smallest structure that meets your real needs and add circulation space to the growing area. For most households six to twelve square metres is enough for salad crops, herbs, a few tomatoes and a propagation area. Buy for the plants you will actually grow, and leave room to expand rather than filling the plot on day one.
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