Greenhouse perimeter-base guide

Understand the three layers

A greenhouse needs a stable relationship between ground, base and frame. The ground or built foundation carries the loads. The perimeter base may raise, align and connect the greenhouse. Anchors tie the assembly to something that can resist wind. A metal plinth on loose soil does not automatically provide that resistance.

Product terminology is confusing: “base included” might mean a galvanised frame, not a paved or concrete foundation. Our guide to what is included helps separate the delivered kit from the site work.

Match the exact product system

Start with the installation manual and technical drawing for your version. Record the base dimensions, required support points, ground-fixing method, door arrangement and whether the base is integral, supplied separately or optional. Nominal feet labels are not accurate construction dimensions. The dimensions guide shows why.

For example, the Palram Hybrid 6 × 4 listing includes a galvanised steel perimeter base, while the Halls Green Frame 6 × 4 listing treats its base as optional. Those distinctions can change the project budget and finished doorway level. Always reconfirm the current listing and manual before ordering.

Choose how to support the perimeter

A perimeter can be carried by a level paved strip, concrete edge, correctly designed timber or another manufacturer-approved ground system. The appropriate choice depends on soil, drainage, wind exposure and anchor requirements. Avoid isolated blocks under corners unless the maker's design explicitly allows them; unsupported runs can sag and rack the greenhouse.

Where soil beds are wanted, keep the interior open but prepare the support line properly. Do not bury the base rail in wet topsoil unless the maker intends that detail. If the site is sloping, soft or waterlogged, seek a groundworker's advice rather than shimming one corner.

Set square, level and at the right height

Measure the two diagonals of the rectangular base; they should agree before the upper frame is assembled. Check long runs with a straightedge, not just a short level at each corner. An out-of-square base can make doors bind and glazing difficult to fit.

Plan finished surrounding path height, the entry threshold and any ramp before setting the base. Raising the structure can create useful headroom but may also create a step. A later path that bridges above the door sill may stop a sliding door or trap water.

Plan anchoring as part of the foundation

Fixings must connect the approved base points to a substrate capable of carrying the relevant loads. The maker may specify ground anchors, masonry fixings or a proprietary system. Do not substitute a convenient bolt merely because it fits the hole. In exposed sites, a professional may need to assess uplift and foundation design.

The anchoring guide explains the practical checks. If you want a solid floor rather than in-ground planting, compare a concrete base or proper paving. The best base is the one that supports the chosen greenhouse and the way you will garden inside it.

Refer to the exact instructions before setting out the support. Halls' foundation guide demonstrates one proprietary approach, but its anchor-leg detail should not be copied into a different frame or ground-base system.