A green roof requires assessment of load capacity, waterproofing, root protection, drainage and maintenance access. Having a flat surface is not sufficient. Assess the complete vegetated build-up, including the condition in which it retains water.
Which type of planting do you intend to add?
Low sedum planting, a flowering roof and an intensively used roof garden are different proposals. They do not require identical build-ups or maintenance. Start with the intended purpose: vegetation, rainwater retention or usable outdoor space. A mood photograph is not a technical specification.
Ask which layers the proposed system contains and which conditions are included in the assessment. A planted assembly can impose different loading when wet than when dry. The responsible professional needs to establish suitability for the existing structure; a generic weight or an online area estimate does not replace that building-specific assessment.
How should waterproofing be assessed beforehand?
Vegetation conceals the roof covering and may make a later defect harder to locate. The condition of the waterproof layer therefore needs to be understood before installation. Ask whether repairs or renewal are needed and how the selected assembly interacts with existing materials. Root protection is a separate consideration and should not be inferred from the colour or broad type of membrane.
Discuss junctions at edges, rooflights and penetrations as well. A planted surface may visually hide these components, but does not replace their technical function. Retain the findings before new layers make the underlying roof less accessible to view.
How should drainage and maintenance be included?
Retaining rainfall does not mean every outlet can be removed or covered. Ask how drainage, emergency provisions and inspection points are arranged within the system. Establish who will carry out maintenance and how suitable access will be provided. Plants also require care; a green roof is not automatically maintenance-free.
Vegetation type and location influence the practical considerations. The maintenance advice should identify the relevant inspections. This avoids discovering after installation that nobody is responsible for a difficult-to-reach outlet or for investigating changing vegetation around an important roof detail that has become obscured by the planting.
Which other intended uses need separate assessment?
A green roof is not automatically a roof terrace. Maintenance access and everyday occupation raise different questions about structure, layout and applicable requirements. State possible future uses early, even if they are outside the first commission. For an owners’ association, establish who can authorise changes to the communal roof.
Request a coordinated record of selected layers, assessments and maintenance arrangements. Any financial support needs a separate check against current conditions. A funding scheme or attractive example project does not establish that this existing roof is suitable without alteration, and should not replace assessment of the particular construction and proposed use.
Frequently asked questions
Is a sedum roof always light enough?
No. Suitability depends on the complete assembly and existing structure. Include the condition with retained water in the assessment.
Can vegetation solve an existing leak?
No. Assess the waterproof layer and junctions first. Vegetation does not replace repair and may make the underlying defect harder to access.
Is a green roof maintenance-free?
Not automatically. Agree on vegetation care, outlets, inspection points and suitable access according to the chosen system and its location.
Consulted 19 September 2026. Check requirements for your own address and selected system.