Planning considerations - Living Roofs in Integrated Urban Water Systems - page 71

• adaptability to harsh climatic conditions, particularly high wind and radiation
(if not shaded);
• drought- resistance through low water demand (if not regularly irrigated), or
drought avoiding (through summer dormancy);
• beneits to desired wildlife and biodiversity;
• resistance to pest and disease;
• acceptable maintenance requirements (meets budget and client expectations);
• adaptability to shallow growing media depth with very hot and very cold root
temperatures;
• tolerance of low fertility;
• provision of acceptable aesthetics;
• selection of fast- establishing plants and long- lived plants. The horticulturalist
should produce a plant design for the living roof that will live for over 20 years.
See Section 4.3 for further information on planting design for living roofs.
3.5 stormwater calculations
Selection of a stormwater calculation methodology is usually arbitrarily dictated
by regulatory requirements and codes. From a regulatory perspective, a living
roof is just one tool amongst a variety of possibilities for managing stormwater.
For consistency and ease of the planning and approval process, a single
framework for determining the effects of SCMs is usually adopted at the
regulatory level. Indeed, in reference to water resources planning and hydrology,
a report by an American Society of Civil Engineers (ASCE) task committee states:
Professional practice rests on acceptance of results and methods by approving jurisdictions.
Practical application requires something that 'works' routinely for speciic areas and
situations, implying technical credibility and authoritative origins. . . . Accordingly, many
day-to-day practices rely on the authority of accepted manuals, handbooks, or textbooks,
and not necessarily current scientiic investigations or recent data.
(Hawkins et al. 2009: 60)
Hawkins et al. (2009) also recognizes that changes are slow to be adopted into
professional practice or jurisdictional guidance. Here again, challenges are
imposed on stormwater planning incorporating GI technologies, despite
champions in research, practice and planning communities.
A review of several stormwater calculation methods commonly adopted by
regulatory agencies is presented in the following sections with respect to how a
living roof might it into each framework, along with their respective beneits
and limitations. These methods are used by stormwater professionals for
submitting permit applications, or demonstrating compliance with technical
stormwater control requirements, and might inluence architectural and structural
design in a living roof project. While in some cases accuracy may be questionable,
or not yet proven, the living-roof-speciic methodologies offered here should be