Architects

The green roof modeler performs a water balance on the green roof system.  It starts with the initial antecedent conditions, then utilizes stochastic weather data to generate hourly water inputs (precipitation), which is further adjusted with factors such as wind, roof slope and orientation.  It then performs a water balance calculation based on the water input, the evapotranspiration rate and the green roof profile, as the various components retain and detain water in different ways.  This can result in positive (runoff) or negative (water deficient) water balance, and the later causes water stress in the plants.​

The StormCap™ Detain 3° is a green blue roof using friction technology for maximum stormwater management. This system is customized to meet project-specific stormwater management with stringent & challenging requirements.

The SpongeBase™ Detention is a non-vegetated system that also provides source control on-site. It uses the void space between impervious surfaces & roofing system and is ideal for rooftop terraces, exposed balconies and walkways.

Ideal when a sizable traditional green roof is in the scope. Adding detention adds incremental cost, only.

Great solution to high groundwater table where storage tank isn’t feasible.

Ideal for sloped properties with limits to where storage tanks can go.

Great solution for brown sites where infiltration or even soil movement is not allowed​.

Ideal for building developments that constitute a large fraction of the site surface, or lot-line-to-lot-line.

Geographic location. Halifax? Toronto? Victoria? Location determines the base design wind speed. ​

Site exposure – presence and density of buildings and trees affect surface roughness and therefore wind speed.​

Building height – the taller the building, the higher the wind speed.​

1. Determine the design wind pressure and design wind speed of your project by looking up in the cladding report or calculate using the equations in NBCC.  These are project-specific design values, based on the geographical location, exposure, importance, openings and height of your project.​

2. Ask your green roof supplier to provide a CSA A123.24 test report of the green roof system that you have specified and look up the wind uplift resistance and wind flow resistance.​

3. Compare the resistance values to the design values as your pass/fail criterion.  If both the uplift and flow resistances are higher than the design values, the GR is good to go.  If any one of the resistances is less than the corresponding design value, the GR is not suitable.​

Fun Fact: NLSM’s green roof specialist Dr. Karen Liu and design ambassador Sasha Aguilera were both involved in the development of this CSA test and are happy to assist.​

The Civil Engineer uses the initial abstraction (IA) values of the different surfaces on the project, including those of extensive and intensive green roofs in the Water Balance calculations for the Stormwater Management Report. Higher IAs are more attractive then lower IAs as the higher the number, the lower the runoff, which means less water goes into the storage tank as “storage volume”. ​ The City requires storage volume of 2.6 m3 to be used within 72 hours to meet the water balance requirement.  Ideally the 2.6 m3 is used up through irrigation re-use, as toilet flushing is much more expensive from what we understand, and not a preferred method for many of our clients. The irrigation demand is sometimes calculated by the landscape architect or Irrigation consultant. Our experienced team is happy to assist.

Yes! It is possible to replace or reduce storage tanks with rooftop systems.  StormCap™+Detention is a multi-tasking detention system. This, combined with the SpongeBase+Detention patio system, makes it possible to replace or reduce storage tanks and free-up valuable real estate. These combined rooftop systems meet water balance and water quality requirements and eliminate the need for a traditional storage tank freeing-up space for extra parking, related revenues, mechanical rooms or EV charging equipment.

NLSM’s green roof specialist Dr. Karen Liu, and design ambassador Sasha Aguilera present free, live educational webinars to industry colleagues. Proof of attendance is issued for Continuing Education Hours (CE), Professional Development Hours (PDH), Continued Professional Development hours (CPD), Structured Learning Hours and Learning Units (LU). Please see the current webinar offerings below, and register free.