Give a roof garden a sound starting brief

Establish who needs to assess the proposal

Ask the owner or building manager what use is approved and what information is needed for a roof-garden proposal. Structural capacity, waterproofing, drainage, edge protection, access, fire and maintenance requirements need building-specific assessment. Local permission requirements may also apply. A gardener's sketch does not replace these checks.

The RHS roof and balcony guide identifies structure, water supply and exposure as key starting issues. Our brief deliberately supplies no load limit, fixing depth or drainage-construction detail.

Keep an inventory of the proposed total: planting systems with saturated medium, retained water, surfaces, furniture, structures, people and equipment. Give the appropriate professionals actual product specifications rather than estimates based only on empty containers.

Choose between a planted roof and a usable garden

Make an allocation drawing without pretending it is a specification

Imagine an 8 × 6 m roof terrace, a 48 m² outline. On the initial sketch, mark the access point, all outlets, services and areas that must remain clear. Leave their required dimensions to the building assessment. Then draw alternative furniture and planting zones within the confirmed usable area.

If a proposed 2 × 3 m seating zone occupies 6 m², that leaves 42 m² of the outline outside that zone. It does not establish 42 m² of spare load capacity or planting space. The distinction between area and capacity is essential: neither the layout tool nor the volume calculator supplies structural approval.

Compare the view from the entrance, a seated position and the maintenance route. Keep planting positions provisional until the professionals responsible for the building have confirmed the constraints.

Use exposure to narrow the planting brief

Record direct sun, reflected heat, wind and sheltered pockets. A roof may combine difficult exposure with very different local corners. Ask for plants and systems appropriate to those conditions and your region, including the winter treatment of roots in containers.

Keep mature height, wind resistance and the support arrangement in the same decision. A tall evergreen screen may promise privacy while creating a much more demanding wind and loading problem. A lower planting group and a different seating position may meet the brief with fewer complications.

For wildlife goals, choose the intended habitat benefit and locally appropriate plants rather than treating any green surface as ecologically equivalent. Establishment water and future maintenance remain part of the proposal.

Write an operating plan before the shopping list

Record who checks watering, irrigation faults, outlets, plant stability and debris, and how they reach those areas safely. Specify who responds during an absence or an extreme-weather warning. A system that can only be inspected by standing in planted areas or moving heavy containers needs redesign.

Keep a seasonal inspection record and follow the building and product maintenance instructions. Do not cover drainage or waterproofing defects with planting. Bring uncertainty back to the responsible professional instead of adding another improvised layer.

Budget for design and assessment, access and transport, installation, water provision, planting, maintenance and replacement. If the building checks do not support the intended use, change the brief. A smaller approved scheme or a different ground-level garden opportunity can be the more practical outcome.