Water Retention

Any construction project or building expansion of an industrial, commercial, institutional, or residential lot must conceive a plan that controls the storm water on private property by using the method mentioned in the by-law RCM-60G-2015. The same regulations will apply to future parking projects as well as modifications to existing parking lots/establishments.

Lots whose impervious surface is less than one thousand square metres (1,000 m²) are exempted from this by-law. The area refers to the surfaces composed of concrete and asphalt, roofs of buildings, and surfaces where such facilities are provided.

Each construction project, when finished, must be subjected to a frequency of rain rate at one in 50 years, and must not add to the water into the sewer network or drainage ditch of the City over the natural maximum flow permitted, which is 10 litres per second per hectare.

The volume required for the retention of stormwater on private property is calculated by using the City designated form, which is available by clicking here (in French only).

The design of rainwater impoundment works shall be done by an engineer who is a member in good standing of the Ordre des Ingénieurs du Québec. The detailed drawing thus prepared must bear the seal and signature of the engineer.

The drawings and the duly completed form prescribed by the City must be submitted along with the building application. The drawings must contain all of the elements noted in Article 42 of the by-law RCM-60F-2016 (click here to consult - PDF 470 KB)

For further information regarding water retention, do not hesitate to contact the Municipal Engineering Division at 514-633-4080.


To consult the integral version of the building by-law RCM-60G-2015 (water retention at section 6), please click here. (PDF – 107 KB)