Installing a greenhouse on a patio

A patio is a location, not proof of a sound base

Paving looks flat from a distance, but a greenhouse is less forgiving than outdoor furniture. A single rocking slab under a corner can twist the frame. Slabs laid on topsoil or isolated bedding dabs can move with wet and dry weather. Before buying, lift your eyes from the attractive paved surface and assess what supports it.

Walk the entire proposed base line and press on each slab. Look for cracks, rocking, sunken corners, open joints and water pooling. If the construction beneath is unknown or visibly weak, get a competent landscaper or groundworker to assess it. Our paving-slab base guide explains what a new foundation should achieve.

Measure the real fit

Get the chosen model's base drawing, overall roof dimensions and door details. Mark the frame and roof on the patio with removable tape or chalk. Leave room for opening vents, gutters, carrying trays and fitting glazing from outside. A compact greenhouse may still block the route to a back gate if placed in the obvious corner.

Check shade from the house, fences and nearby trees. A south-facing patio can run hot on sunny days, while an enclosed shaded yard may offer less light than expected. Plan ventilation and water collection from the beginning.

Check level and drainage

Use a long straightedge and level across the full frame footprint. Patios commonly have a fall for water drainage, but the greenhouse base requires a level support plane within its manual's tolerance. Do not build a visibly twisted frame to follow the paving. A designed level support may be possible, but the detail must preserve stable load transfer and doorway access.

Do not solve the level problem by piling loose packers under corners. Also check where rain will flow after the greenhouse intercepts it. Keep runoff out of the doorway, away from the house and off neighbouring land.

Plan approved anchors

The greenhouse needs the anchoring specified by its manufacturer. Suitable masonry fixings need sound material, adequate edge distance and an appropriate underlying structure. Drilling into a thin, cracked or loose slab does not make it secure. Avoid slab joints and edges unless the approved design explicitly addresses them.

Fixing type and depth are site- and product-specific. Ask the manufacturer or competent installer when the patio construction is uncertain. The anchoring guide covers the sequence and common errors. Do not rely on pots or staging as ballast in place of approved restraint.

Preserve everyday access

A patio greenhouse must still be pleasant to use. Check that the door opens fully and can be approached with a watering can or barrow. A low threshold is of little benefit if the paving immediately outside has a raised edge. Keep a working strip around the roof and gutter.

If the patio is raised, cantilevered or built over a cellar, treat it as a structural question rather than ordinary ground-supported paving. The decking guide sets out why elevated platforms need separate assessment. Finally, check the planning guide for the rules applicable to your property.

The Halls base guidance reinforces the need to check the support before assembly. A patio's appearance does not establish that its slabs, bedding and fixing positions suit your own greenhouse.