Cool roofs reflect the sun’s rays and reduce heat build-up through a light coloured or highly reflective roofing product such as a coating, new membrane or shingle.
Most roofs in Canada are dark in colour and absorb heat from the sun’s rays transferring it into the rooms below. Because cool roofs are better at reflecting the sun’s energy, less heat is transferred inside your home. As a result, you may not have to use your air conditioner as much, saving you energy and reducing greenhouse gas emissions. Cool roofs also increase the life expectancy of your roof, because they reflect the heat and UV rays that damage and age roof materials.
Dark-coloured roofs in high-density areas also contribute to the urban heat island effect – significantly warmer temperatures in urban areas compared to rural areas. As a result of climate change, Ottawa is expected to see dramatic increases in the number of extremely hot days due to continued global warming. Installing a cool roof is one way to help to offset this.
There are cool roof options for all types of roofs, including steep slope (pitched roofs), low slope (flat roofs).. Roofing products are tested for their reflectivity and given a Solar Reflective Index (SRI) value between 0-100. The higher the number, the more reflective it is.
If you want to convert an existing roof into a cool roof, you have the following options:
- Retrofit your existing roof – apply a coating that is waterproof and has reflective properties
- Replace your existing roof – install a new cool roof using a reflective roof product.
What to Look For
- Low slope or flat roof – look for cool roof products with a SRI value of 78 or greater. Options include single-ply membranes, stone white calcite gravel, fluid applied membranes or a coating of white reflective paint.
- Steep slope or pitched roof – look for cool roof products with a SRI value of 25 or greater. Options include asphalt shingles, metal, tile, shake, among others.
- Products with a thermal emittance or emissivity of greater than or equal to 0.9
- Products that are asbestos and mercury-free and emit zero volatile organic compounds (VOCs) and ozone-depleting substances.
- You can search for cool roof products using the Cool Roof Rating Council’s directory.
Things to Consider
- Switch to a cool roof when your roof needs replacement, as converting a standard roof that is in good condition to a cool roof isn’t cost-effective.
- If your roof is not ready to be fully replaced, consider applying a cool roof coating.
- Like all roofs, the condition of your cool roof must be assessed each year and cleaned (if required) to maintain its high reflectivity.