What is a blue roof, and how can it help your business?
You might have heard of green roofs—growing plants on the roof to insulate the building, reduce the heat island effect and absorb carbon emissions.
Now there’s a new twist on this idea: blue roofs. It’s a pioneering concept of storing rainwater on your roof. The goal is to control runoff to reduce flooding risks from backed-up stormwater pipes, a major source of business insurance claims.
Blue roofs are more affordable than green roofs and offer numerous sustainability benefits. These include reduced air conditioning and heating costs because of the insulating effects of the stored water. Businesses can also reduce their water bills by using rainwater for toilets, irrigation, cooling towers, and cleaning needs.
Blue roofs case study
Company: Enviro-Stewards
Action: Installed smart blue roof
Results: Reduced emissions by 15% per employee and lowered
The number-one insurance claim in Canada is for flooding, and it's doubled in the last 10 years.
Bruce Taylor
President, Enviro-Stewards
“Blue roofs are more proof that sustainability innovation is everywhere,” says Bruce Taylor, president of Enviro-Stewards, an environmental consulting firm. He said his own business was able to cut its water, air conditioning and heating bills significantly after he worked with his landlord to install a blue roof during a roof renovation. The company was able to reduce its emissions by 15% per employee, thanks to its demonstration of an “affordable smart blue roof,” as Taylor calls it.
Blue roofs are still a relatively novel concept, with only a few examples worldwide so far. But Taylor says there’s growing interest among businesses and insurance companies.
Taylor’s company is now installing a smart blue roof for Credit Valley Conservation, a conservation authority in Mississauga, Ontario. An insurance industry association is covering the costs as part of a pilot project due to the potential for reducing flood damage risks.
“The number-one insurance claim in Canada is for flooding, and it's doubled in the last 10 years,” Taylor says.
When you get a 100-year storm more frequently due to climate change, the stormwater system wasn’t designed for that and it overflows and creates a lot of damage.
Bruce Taylor
President, Enviro-Stewards
What is a blue roof?
Definition: A blue roof stores rainwater on a flat roof.
Purpose: To control runoff in order to reduce flooding risks.
Components: Valves, sensors and containment barriers.
A blue roof is a type of roof that is adapted to store rainwater. Valves are installed on stormwater drains to control flow during a rainstorm. The idea is to prevent storm pipes from backing up, which can cause flooding damage to the building and send untreated water into rivers and lakes.
“We’re getting more intense and frequent storms due to climate change,” Taylor says. “The system wasn’t designed for that, and it overflows and creates a lot of damage.”
Blue roof technology involves installing a small dam-like structure on the roof to collect and contain rainwater. Water depth typically remains below 10 or 15 centimetres. “It would be hard to get more than a few inches because it’s constantly evaporating,” Taylor says.
Your roof is literally a swimming pool liner that is storing water.
Bruce Taylor
President, Enviro-Stewards
Sensors are installed to detect leaks, measure the water level, gather data on energy savings and gauge weather conditions (hence the term “smart blue roof”). The data can be monitored remotely, and the water can be drained in advance if a storm is expected.
“We put a weather station on the roof,” Taylor says. “If my weather data says there’s an inch of rain coming, I can drop an inch of water down the storm drain before it starts to rain. Then I can take 100% of that storm when it comes.”
Pipes and valves can also be installed to allow building occupants to use the water for business needs, such as for toilets, irrigation, cooling towers and cleaning machines and equipment.
A blue roof can only be installed on a flat roof, not a peaked one. Buildings built to code generally have enough load-bearing capacity and are adequately sealed against water infiltration, allowing for a blue roof. An installer typically checks the building’s existing roof for structural integrity and the membrane for leak detection before proceeding with the installation.
Your building isn’t as hot with a blue roof, so your air conditioning isn’t working as hard.
Bruce Taylor
President, Enviro-Stewards
The water containment area can cover all or part of a roof, depending on whether other structures or equipment are present on top of the building. For example, if mechanical equipment is located on the roof, the containment area can be built around it.
Water is typically drained off before winter.
If a roof is peaked or otherwise unsuitable for a blue roof, an alternative option is to set up a rainwater harvesting tank. This can be used to divert rainwater from your storm pipes and provide water for business uses. For example, rainwater tanks on the city of Guelph’s bus terminal are used to wash buses in the building. Taylor notes that rainwater is actually better than city water for washing buses, as the (naturally distilled) rainwater reduces the need for spot remover.
Is a blue roof safe?
A blue roof is at least as safe as a conventional roof, Taylor says. Leak sensors are installed to detect any water infiltration. “We know right away if it leaks, which isn’t necessarily the case for a roof without a sensor,” he says.
Canadian building codes require roofs to be sealed against water infiltration and be strong enough to bear typical snow loads.
A structural engineer inspects the roof to ensure it has building code compliance and can support a blue roof. “If your building was built to code, it can hold this,” Taylor says. “Your roof is literally a swimming pool liner that is storing water.”
Additionally, a building with a blue roof is less prone to stormwater pipes overflowing and causing indoor flooding damage.
What are the benefits of a blue roof?
5 key benefits of installing a blue roof:
- Reduces the risk of flood damage
- Cuts energy bills
- Lowers water bills
- Extends roof membrane life
- Supports sustainability certifications
Reduces the risk of flood damage
A blue roof’s key advantage is controlling stormwater pipe runoff to reduce the risk of flood damage, which can be costly and disruptive to a business, leading to higher insurance premiums. Leak sensors installed with a blue roof alert you to water infiltration, further reducing the risk of water damage. In urban areas, especially, where heavy rainfall can overwhelm drainage systems, blue roofs act as a buffer. They do this by temporarily holding water and releasing it gradually.
This not only protects individual properties—communities can benefit, too. Blue roofs lower the likelihood of neighbourhood-wide flooding events. They also help ease pressure on municipal infrastructure and reduce costs.
“The conventional approach to increasing storm drain capacity is to retrofit the stormwater infrastructure. You have to dig up the street, put in bigger pipes, take somebody's property, build a pond on it, dredge it every few years,” Taylor says. “It’s a lot less expensive to reduce the runoff at the source.”
Cuts energy bills
A blue roof acts as an insulation barrier that moderates temperatures inside the building. That can reduce your air conditioning and heating use and increase the service life of those systems.
Taylor provides an example to illustrate the impact a blue roof can have. One warm spring day when the outside temperature was 30°C, he measured the temperature of the black tar-and-gravel roof covering part of a building. It was a sizzling 60°C. On a renovated section of the same roof, which had a white roofing membrane, the temperature was lower but still fairly hot, at 40°C. On the same roof, a bucket of water had a temperature of 20°C. That was cooler than the temperature inside the building, which was 25°C.
“Your building isn’t as hot with a blue roof, so your air conditioning isn’t working as hard,” Taylor says.
Lowers water bills
Water stored on a blue roof can be used for business purposes, potentially reducing your water usage and associated costs. Taylor said his building’s blue roof provides water to toilets and a “living wall”—a wall of plants—in his business, so he doesn’t need to use any municipal water. And the plants are healthier than those that live on comparable living walls that use city water.
Installing a blue roof may allow you to be credited on municipal stormwater charges and benefit from water conservation incentive programs.
Extends roof membrane life
Less heat may prolong the life of your roof’s waterproof membrane. By holding water on the surface, a blue roof helps regulate the roof temperature, reducing the extreme heat and cool cycles that often cause roofing materials to crack, blister or deteriorate prematurely.
This protection from thermal stress can significantly extend the service life of the membrane, saving building owners from costly repairs or early replacement. In addition, the water layer shields the membrane from direct exposure to ultraviolet (UV) rays, which are another significant contributor to roof degradation. Over time, this combined protection ensures that the roof maintains its integrity and performance, offering both environmental and financial benefits.
Supports sustainability certifications
Having a blue roof helps your business hit sustainability goals for certification, reporting and social entrepreneurship purposes. Many certification programs, such as LEED, Energy Star or BOMA BEST, value effective stormwater management, energy efficiency and resilience measures. By incorporating a blue roof into your building design, you can demonstrate tangible environmental action that strengthens your case for accreditation. It also provides clear data for sustainability reporting, showing measurable steps toward reducing your organization’s environmental footprint.
Your sustainability efforts can also foster goodwill among customers, employees, stakeholders, and the community. Customers may feel more confident in supporting a company that actively reduces its environmental impact. Employees may take pride in working for a forward-thinking employer, and local communities benefit from reduced flooding risks and improved stormwater management. In this way, the investment in a blue roof not only supports certification but also builds long-term trust and reputational value.
If you were replacing the roof anyway, the extra cost of a blue roof is likely to be paid off from the savings.
Bruce Taylor
President, Enviro-Stewards
How can I install a blue roof?
A blue roof installer typically starts with a feasibility study to determine if a building can support a blue roof or needs any roof renovation. The study also outlines a design for the blue roof, costs and quantifies potential savings.
Next, the installer does a detailed design, obtains permits and builds the roof. They typically remain involved to help monitor sensors, operate valves and maintain the system.
How much does a blue roof cost?
The cost can vary greatly depending on the contractor and the type of blue roof. A blue roof with a basic water containment area, including pipes, sensors, and valves, costs about $1 to $2 per square foot, Taylor says. Renovating the roof to bring it up to code is an additional cost.
“If you were replacing the roof anyway, the extra cost of a blue roof is likely to be paid off from the savings of a lower water bill, and reduced heating and air conditioning,” he says.
What is the difference between a green roof and a blue roof?
A green roof is a roof that has been converted to a green space. It typically includes a roof barrier, drainage and irrigation systems, a growing medium and plants. It generally costs $10 to $20 per square foot to build, about 10 times more than a blue roof.
A blue roof stores rainwater on top of a building. It generally consists of a small barrier to contain the rainwater, along with sensors, pipes and valves.
Green roof vs. blue roof
| Feature | Green roof | Blue roof |
|---|---|---|
| Function | Plant-based insulation | Rainwater storage |
| Cost | $10–$20/sq ft | $1–$2/sq ft |
| Components | Plants, irrigation, Drainage | Valves, sensors, containment |
| Benefits | Heat island reduction | Flood control, water reuse |
Next steps
Energy-efficient retrofitting of your existing commercial building can be one of the most effective ways to lower your commercial real estate costs, boost business revenues, and protect the environment. Use the BDC Building Retrofit Savings Calculator to find out more about the long-term benefits of reducing your environmental footprint.