Study: Blue-green roof pilot project

We partnered with the British Columbia Institute of Technology (BCIT) to conduct a 2-year study from January 2020 to December 2021.

The study took place at Helena Gutteridge Plaza at City Hall, analyzing the thermal and rainwater management performance of a blue-green roof in our west coast climate.

Types of roofs tested
Four roof assemblies were constructed at the plaza:
Each assembly was equipped with sensors to record temperature, water runoff, and soil moisture.

Components of each roof type
- Green and blue-green roofs used a vegetated growing medium (sedum mats on top of 100 mm and 75 mm soil, respectively).
- Blue and blue-green roofs used an 85 mm water storage layer.

Pilot summary of results

Study limitations
- Results reflect the scale and design details of the test roofs and may not reflect general performance.
- Roof size and other design changes may improve performance.
Vegetation health and irrigation
- Blue-green roof water storage layer helped maintain healthier, more vibrant vegetation compared to the green roof.
- Blue-green roof remained moist and healthy up to 3 weeks longer during drought, compared to green roof, and experienced wilting for only 2 to 3 weeks in August.
- The sedum (type of succulent) on the vegetated roofs survived both the 2020 and 2021 droughts. No additional irrigation was required.
Surface temperature performance
- Conventional roof peak surface temperature reached over 63°C
- Vegetated roofs (Blue-green and green) significantly cool peak surface temperature by up to 50% during spring and summer months, compared to the conventional roof.
- Water is important. Surface temperature is similar to a conventional roof when the growing medium dries out.
Internal temperature performance
- Vegetated roofs kept internal temperature above zero and warmer than non-vegetated roofs in the winter months.
- Vegetated roofs and blue roofs had internal temperatures up to 4°C cooler in the summer months compared to a conventional roof.
Rainwater management performance
Even though each roof type retained less water during the winter, they still captured enough rainfall throughout the year to be beneficial overall.

Average rainfall retention for each roof type over a 2-year period
- Green roof (23%)
- Blue-green roof (20%)
- Blue roof (17%)

Reports

An Experimental Field Study on the Thermal & Water Balance Performance of Vegetated Roof System by Harveer Singh Takhar

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Study: Blue-green roof pilot project

Types of roofs tested

Pilot summary of results

Study limitations

Vegetation health and irrigation

Surface temperature performance

Internal temperature performance

Rainwater management performance

Reports

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