• Welcome to the new and improved Building Code Forum. We appreciate you being here and hope that you are getting the information that you need concerning all codes of the building trades. This is a free forum to the public due to the generosity of the Sawhorses, Corporate Supporters and Supporters who have upgraded their accounts. If you would like to have improved access to the forum please upgrade to Sawhorse by first logging in then clicking here: Upgrades

Flow control roof drains allowed to install with declaration where the maximum drain down time exceeds 24 h


Registered User
Apr 21, 2022
This is from Ontario building code Division B part 7:
----------------------------------------------------------------------------------------------------------------------------------- Hydraulic Loads from Roofs or Paved Surfaces
(2) Flow control roof drains may be installed provided,
(a) the maximum drain down time does not exceed 24 h,
(b) the roof structure is designed to carry the load of the stored water,
(c) one or more scuppers are installed not more than 30 m apart along the perimeter of the building so that,
(i) the scuppers are designed to handle at least 200% of the 15-minute rainfall intensity, and
(ii) the maximum depth of controlled water is limited to 150 mm,
(d) they are located not more than 15 m from the edge of the roof and not more than 30 m from adjacent drains, and
(e) there is at least one drain for each 900 m2.

1. In the above (2), the code states "may be installed provided", which should be understood as: if the conditions listed are not provided, Flow control roof drains are not allowed to install, is this understanding correct?

2. If the understanding of question 1 is correct, why there are many municipalities allow Flow control roof drains to be installed by requesting a declaration from engineers and architects, where the condition "(a) the maximum drain down time does not exceed 24 h" is not met, such as the following declaration (see scenarios 3 on the first page)?