4.7.6 Construction

Construction sequencing is critically important for vegetated roof construction, because numerous trades are involved, each with their particular roles and potential conflicts during construction. For example, construction may require coordination among a general contractor, landscape contractor, roofing contractor, leak detection specialist, irrigation specialist, HVAC contractor, and construction inspectors, all of whom require access to the roof areas at various times during construction.

The waterproof membrane must be protected once installed, and should be tested prior to placement of the growth media and other subsequent vegetated roof materials (WSU-PSP, 2012). There are many ways of establishing plants in a vegetated roof. The most common methods of plant establishment include:
  • Direct application of seed or cuttings.
  • Planting of pot-grown plants or plugs.
  • Laying of pre-grown vegetation mats or grids.

Making the roofing contractor responsible for the vegetated roof installation, either directly or by means of subcontracted services, can help ensure that the integrity of the waterproof membrane is maintained during construction.

Off-the-shelf vegetated roof products are have become popular as roofing companies seek to fill the growing demand for vegetated roofs. Off-the-shelf products are typically installed by roofing contractors that are licensed by the company that furnished or grew the vegetation mats or trays. Where off-the-shelf roof systems are selected, the product design will be provided by the company that grew the vegetation mats or trays based on the microclimatic conditions provided by the civil engineer and the building design provided by the architect and structural engineer.