Trees on a roof terrace: plan the structure, water and future care

The appealing part of a roof garden is easy to picture: shade beside the dining area, greenery outside the bedroom and somewhere to sit above the street. The less visible part is what keeps it working. Soil retains water, drains need attention and a large plant may eventually need replacing. These questions belong at the start of the design.

For a home in Spain, treat an elevated garden as a coordinated building and landscaping project. This is a briefing checklist for the owner, not a method for calculating a roof's capacity. A competent professional needs to assess the actual structure and proposed installation.

Write the purpose before choosing the planting

Decide what you need the garden to do. Shade, privacy, a view from indoors and a place for gardening are different briefs. Tell the designer when the terrace will be used and who will look after it. If you expect to leave the property empty for months, the care arrangements need as much thought as the summer appearance.

Ask for alternatives where appropriate, comparing the same practical outcome. A smaller planting scheme or a separate shade structure may change maintenance and cost, although neither can be assumed suitable without design work. Include the terrace brief in the basic and execution project stages early enough to coordinate the space below it and the building services.

Get a location-specific structural answer

Provide the assessor with the proposed layout and information about containers, planting media, irrigation and mature vegetation. The assessment needs to consider relevant loads and their distribution through the actual building. Do not turn a general roof loading figure into permission for any planter. Spain's CTE DB-SE-AE is the official reference for actions on buildings; its application requires project-specific judgement.

Ask for an approved layout and a clear description of changes that require another review. Moving several heavy containers into one corner can differ from the agreed arrangement. This matters on unconventional structures too: a converted shipping-container home does not gain a usable roof garden simply because its original container was designed for transport. The altered building and intended use must be assessed together.

Follow the water all the way to its outlet

Request a section showing how the planting arrangement relates to waterproofing, protection, drainage and inspection points. Ask where excess irrigation goes and how an obstruction would be noticed and cleared. The roof contractor and irrigation installer should work from a coordinated detail, rather than assuming the other trade has dealt with the connection.

The CTE DB-HS covers moisture protection and drainage matters. A designer must select the suitable arrangement for your building. When an inverted flat roof is involved, establish how the proposed planting fits its layers. Think beyond the initial leak test: a repair that requires a crane and removal of the entire garden is a different maintenance proposition from an accessible local intervention.

Specify the future plant, not just the delivery size

A landscaper needs information about sun, shade, wind exposure, water supply and the available root space. A species seen thriving at ground level nearby is not automatically appropriate for a constrained, exposed terrace. Ask how the planting is expected to develop, what care it needs and whether its eventual size remains compatible with the available space.

Distinguish the appearance on installation day from the privacy shown in a mature design image. Discuss pruning, leaf fall around outlets and replacement. Access for care must be safe and realistic; do not accept a maintenance plan that depends on you improvising work at a roof edge. If specialist visits are needed, identify their scope and include them in the ownership budget.

Rehearse delivery and eventual removal

Have the installer inspect the route from the unloading point. Doorways, lifts, stairs and a place to manoeuvre may restrict what can be delivered. Where lifting equipment or use of public space is necessary, ask the contractor to identify the practical arrangements and applicable permissions before you order. A quotation headed “delivery included” needs a defined delivery point.

Then run the scenario backwards. Could the container or tree be removed after the building is occupied and the façade is complete? Some initial installations depend on access that will disappear. Record a future replacement method rather than leaving it to the next owner. The relationship between supports, structure and the building project remains important even when the finished surface looks like an ordinary garden.

Build a quotation that exposes the missing work

Separate design and checks, preparation, waterproofing, drainage, irrigation, plants, containers, lifting, installation and care. Mark items already included in the main building contract to avoid double counting. Compare initial establishment visits with ongoing maintenance as different services, and ask what happens if a plant needs replacement.

For an illustrative comparison, imagine two offers delivering the same privacy screen. One includes scheduled maintenance and the other stops at installation. Obtain the missing service price before judging the difference. There is no meaningful universal installed price for an undefined roof garden. Add actual proposals to the project budget calculator and label unresolved allowances clearly.

Finish with instructions the owner can use

Collect the approved arrangement, product references, care instructions, checks and relevant contacts. Establish who may approve a change in planting or containers. Where several firms are involved, align their responsibilities with the building contract scope so a future problem is not passed indefinitely between trades.

Keep these records available to whoever cares for the property while you are away. If an elevated garden is part of your plans, tell us about the home, whether the roof already exists and what you want the planting to achieve. Those details make the next conversation much more useful.