Green roofs in Portugal should be chosen as complete systems: structure, waterproofing, root protection, drainage, substrate, vegetation.
Green roofs in Portugal should be chosen as complete systems: structure, waterproofing, root protection, drainage, substrate, vegetation, irrigation, access and maintenance. The distinction between extensive and intensive helps, but it does not settle exposure, wind, fire or water availability.
Extensive and intensive
An extensive roof uses a shallower depth and low vegetation, with lighter loads. An intensive one allows more substrate, shrubs and use, coming close to a roof garden. Between the two there are intermediate systems.
The structural capacity must be checked by the competent specialist discipline.
The Portuguese climate and water
Dry summers, wind and high radiation can make plant palettes copied from wetter climates inadequate. Even tolerant species need water during establishment and may require back-up irrigation.
Drainage must work in heavy rain and the system needs an overflow.
Vegetation, fire and maintenance
A build-up of dry biomass can increase risk. Safety strips, plant selection and maintenance must be integrated with fire and access requirements.
The roof needs inspection of outlets, replacement planting, weed control and monitoring of the waterproofing.
Responsibilities and warranties
The design must define who is responsible for the structure, waterproofing, drainage, irrigation and vegetation. Without this division, a plant failure can hide a drainage problem and a leak can be wrongly blamed on maintenance.
Before handover, outlets and overflows must be tested, thicknesses confirmed and an access plan delivered. Plant maintenance cannot depend on crossing areas with no protection or anchor points.
The selection of vegetation should come with a replacement strategy. On exposed roofs, some losses are to be expected; the system should allow replacements without damaging the waterproofing or depending on species that are hard to obtain.
Critical points
The most common mistakes are selecting plants before knowing the depth; doing without irrigation because sedum is used; ignoring wind and fire; and not providing for service access.
Applying it to the project
At Diaplant, the work centres on selecting and planting the vegetation, in coordination with the designer and with the supplier of the roof system. The structural solution must be sized by the discipline responsible.
A green roof is built and planted infrastructure. The vegetation only works when all the layers and responsibilities are coordinated.
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