01-40_WC_149_JUL-AUG26_PT - Flipbook - Page 34
”Asclimatepressuresintensify,thequestionisnolonger
whethercitiesshouldadoptinnovativestormwater
solutions,butwhetherourpoliciesareevolvingquickly
enoughtosupportthem”
The Credit Valley Conservation smart blue roof in Mississauga includes all three treatment
steps, ensuring that water remains treated and monitored while stored on the roof.
34
WATER C AN ADA • JULY/AUGUS T 2026
Blue roofs are engineered systems designed to
temporarily store rainwater on rooftops, either
through controlled drainage technologies or simple
ballast-filled trays. By slowing runoff, they help reduce
pressure on sewer systems and mitigate flooding
risks. Over time, they can also contribute to building
cooling, energy savings, and reductions in the urban
heat island effect. Importantly, these benefits are
optimized when water can be stored for longer
periods and released strategically, either ahead of
potential future storms or for potential reuse.
Yet Canadian building and plumbing codes
impose a significant constraint. Water detained
on rooftops must typically be drained within 24
hours, a provision known as the drawdown time
requirement. At first glance, this rule aligns with
public health priorities, and as a public health
researcher, I appreciate the precautionary intent.
However, a closer look suggests that the requirement
may be overly conservative for modern smart blue
roof systems.
Both the National Plumbing Code (NPC
2.4.10.4) and the Ontario Building Code (OBC
7.4.10.4) connect this requirement to Health
Objective 2, which aims to limit illness risks
associated with unsanitary conditions. However,
the NPC’s intent statement primarily warns that
inadequate drainage could result in stagnant water,
leading to mould or mildew growth and potential
harm to occupants.
Here lies the tension. Many advanced blue roof
systems are designed to prevent stagnation. Many
incorporate recirculation alongside treatment
processes such as filtration, ultraviolet disinfection,
and chlorination. For example, the Credit Valley
Conservation (CVC) smart blue roof in Mississauga
includes all three treatment steps, ensuring that water
remains treated and monitored while stored on the roof.
Notably, the codes provide little detail beyond
mould and mildew. Few water quality parameters are
explicitly addressed, leaving developers and public
health professionals to navigate unclear and vague
guidance. When examining the broader regulatory
logic behind the 24-hour rule, it becomes clear
that the requirement is heavily rooted in structural
concerns. Stored water adds weight, and timely
drainage reduces the risk of roof failure, material
degradation, and flooding. However, this logic was
largely developed with traditional roofs in mind,
systems that lacked monitoring, treatment, and
operational control.
WATERCANADA.NE T
TMU
STORMWATER
