To fight urban heat islands, many Montreal boroughs require a replaced flat roof to be white or a light reflective colour, a green roof, or covered with light-coloured gravel ballast. Rules and exceptions vary by borough: check them before choosing your membrane, and have your roofer confirm.
Why a white roof?
A black roof can get scorching hot in summer, heating the top floor and the neighbourhood. A light roof reflects much of the sun’s energy, keeps the unit below cooler and reduces thermal stress on the membrane.
What the rules usually require
- A white or light covering with a minimum solar reflectance
- Or a green roof
- Or light-coloured gravel ballast
- Possible exceptions depending on slope, use or building type
Which membranes comply?
White TPO is naturally very reflective. Elastomeric membranes come with white or light granules made for these rules. Standard EPDM is black and fits less well. See elastomeric vs TPO vs EPDM.
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General information. Municipal bylaws change and vary by borough: check with your borough before work starts.