A Proven Approach to Managing Solar Heat
A cool roof is a roofing system designed to reflect more of the sun’s energy and absorb less heat than conventional roofing.
Traditional dark roofing materials can absorb a substantial amount of incoming solar energy. As the roof becomes hotter, some of that heat is transferred into the building and some is subsequently released into the surrounding environment.
Cool roofing changes this relationship by using roof surfaces with higher solar reflectance and, where applicable, high thermal emittance. Instead of absorbing and storing as much solar heat, the roof reflects a greater proportion of incoming solar energy and more effectively releases heat that it does absorb.
The result is a roof surface that can remain substantially cooler under strong sunlight.
Cool Roofing by the Numbers
Common Cool Roofing Terms
Solar Reflectance
Solar reflectance describes the ability of a roofing surface to reflect incoming solar energy rather than absorb it as heat. A roof with higher solar reflectance sends more of that energy away from the roof, reducing the amount available to heat the roofing system and building below.
Solar Reflectance Index (SRI)
Solar Reflectance Index, or SRI, is a calculated value based on two separately measured properties of a roofing material: solar reflectance and thermal emittance. Using a standardized calculation, SRI indicates how hot a roof surface is expected to become in sunlight compared with reference black and white surfaces. In general, a higher SRI indicates a cooler-performing roof surface under the specified conditions.
Thermal Emittance
Thermal emittance describes the ability of a surface to release absorbed heat. Roofing with high thermal emittance can more effectively release the heat it does absorb. Combined with high solar reflectance, this helps reduce how hot a roofing surface becomes when exposed to sunlight.
Better Understanding Cool Roofing
Figure 3. Effects of a cool roof versus a dark roof.
Source: Global Cool Cities Alliance (2012), with data from Lawrence Berkeley National Laboratory.
Does a Cool Roof Have to Be White?
White roofing generally provides the highest solar reflectance, particularly for low-slope roofing systems, but cool roofing is not limited to white roofs.
Modern roofing technologies can use specially formulated surfaces and pigments that reflect portions of solar energy, including near-infrared energy that cannot be seen by the human eye. This makes it possible to produce roofing in a range of colours while providing greater solar reflectance than comparable conventional products.
However, colour still matters. As roof colours become darker, achievable solar-reflective performance generally declines. Roofing type also matters: a light-coloured membrane, coating or metal roof can achieve substantially higher performance than many asphalt shingles, even when those shingles are marketed as cool-roof products.
The central point is that two roofing products that appear to be a similar colour can perform differently, and a product that represents an improvement over a conventional dark roof may still perform far below a high-reflectance white roof. SRI allows building owners, designers and roofing professionals to compare actual measured performance.
Cool Roofing Is a Passive Technology
One of the defining characteristics of cool roofing is that its heat-reduction effect is passive.
Once installed, the reflective roof surface does not require electricity, mechanical equipment or occupant action to reduce solar heat absorption. Whenever solar radiation reaches the roof, the surface characteristics of the roofing determine how much of that energy is reflected and how much is absorbed.
Cool roofing does not replace air conditioning or other measures needed to protect people during dangerous heat. It does, however, reduce one of the principal ways solar heat is absorbed by buildings and accumulated across developed areas.
Asphalt Shingles — An Important Performance Limitation
Not all roofing technologies can currently achieve the same level of cool-roof performance.
Asphalt shingles, which are widely used on steep-slope residential and light-commercial roofs throughout British Columbia, present a particular challenge. Conventional asphalt shingles are generally dark, solar-absorbing products, and most have much lower SRI values than white membranes, reflective coatings and many high-performance metal roofing products.
Higher-reflectance asphalt shingles have been developed for jurisdictions that recognize or require cool-roof performance. These products can represent a meaningful improvement over conventional dark shingles. Even so, their SRI values are generally much lower than those achievable with highly reflective low-slope roofing systems.
This distinction is important: a roofing product can legitimately provide improved cool-roof performance without approaching the thermal performance of a white or very highly reflective roof.
The British Columbia Product-Recognition Gap
Cool-roof performance cannot become a routine consideration in British Columbia if higher-performing products are not routinely recognized, specified, promoted or made readily available in the local roofing market.
This is particularly evident in steep-slope asphalt roofing. While rated higher-reflectance shingle products exist, cool-roof performance is not yet a normal product-selection criterion in much of the British Columbia market. Building owners may therefore receive little or no information about solar reflectance or SRI when selecting a replacement roof.
A core educational role for CoolRoofsBC is to help move roof selection beyond colour and appearance alone and toward greater awareness of measured solar performance, appropriate product choices and the opportunities available when roofs are replaced.
Cool Roofing - A Passive Technology
One of the important characteristics of cool roofing is that its heat-reduction effect is passive. Once installed, the reflective roof surface requires no electricity, mechanical equipment or occupant action to reduce solar heat absorption. Whenever sunlight reaches the roof, its surface properties determine how much solar energy is reflected and how much is absorbed as heat. Cool roofing complements rather than replaces other measures used to protect buildings and occupants during extreme heat.
Cool Roofing Does Not Need to Be White
White roofing generally provides the highest solar reflectance, particularly on low-slope roofs, but a cool roof does not have to be white. Modern roofing technologies can use specially formulated surfaces and pigments to provide improved solar reflectance in a range of colours. Colour still matters, however: achievable reflective performance generally declines as roofing becomes darker. Measured performance, rather than colour or appearance alone, provides the better basis for comparing roofing products.
Asphalt Shingles and Cool Roofing
Asphalt shingles, widely used on BC steep-slope roofs, present a particular cool-roofing challenge. Conventional shingles are generally dark and solar absorbing, with substantially lower reflective performance than white membranes, reflective coatings and many high-performance metal roofs. Higher-reflectance shingles are available and can provide meaningful improvement over conventional products, but they generally do not achieve the performance possible with highly reflective low-slope roofing systems. Different roofing technologies therefore need to be compared realistically.
The BC Cool Roof Recognition Gap
Higher-performing roofing products cannot become routinely considered in BC if their solar performance is not readily recognized, specified or promoted. This is particularly apparent with steep-slope asphalt roofing, where owners may receive little information about solar reflectance or SRI when choosing a replacement roof. Greater awareness of measured solar performance would allow building owners, designers and roofing professionals to make more informed comparisons alongside the traditional considerations of appearance, durability, warranty and cost.
What Types of Cool Roofing Are Available?
Cool roofing is not a single roofing product. It is an approach to roof-surface performance that can be incorporated into different roofing systems for both low-slope and steep-slope roofs, depending on the building, roofing assembly and products available.
Reflective single-ply roofing membranes;
Reflective roof coatings;
Reflective or specially coated metal roofing;
Cool-coloured tiles; and
Higher-reflectance shingles and other roofing products engineered to improve solar performance.
Cool Roofing for New and Existing Buildings
Existing Roof – White Coating
Dark Membrane Roofing to White
New & Replacement Roofing Membranes
High SRI Rated TPO & PVC Systems
Asphalt Shingle Roofs
Higher SRI Rated Options
Benefits Cool Roofing Provides to Buildings and Communities
Benefits Cool Roofing Can Provide
Cool roofs can provide benefits both to individual buildings and to the communities in which they are located. These benefits can include lower roof temperatures, improved indoor comfort, reduced cooling demand, support for rooftop solar, reduced urban heat and greater resilience during extreme heat. The extent of these benefits will vary depending on climate, building design, insulation, roof type, occupancy and other factors.
Building Benefits
Lower Roof Temperatures
By reflecting more solar energy and absorbing less heat, cool roofs can remain substantially cooler than conventional dark roofs under sunny conditions. The U.S. Environmental Protection Agency (EPA) reports that highly reflective and emissive cool roofing materials can remain approximately 50 to 60°F (28 to 33°C) cooler than traditional roofing materials during peak summer weather. Conventional black asphalt roofs can reach midday surface temperatures of approximately 165 to 185°F (74 to 85°C), while high-reflectance, high-emittance cool roofs may remain closer to 110 to 115°F (43 to 46°C) under comparable conditions.
Improved Indoor Comfort
Reducing the amount of heat entering through a roof helps keep interior spaces cooler during prolonged periods of hot weather and extreme heat events. This can be particularly beneficial in buildings that lack adequate mechanical cooling. In one Sacramento two-storey apartment study cited by the EPA, installation of a cool roof reduced peak attic air temperatures by 30 to 40°F (17 to 22°C), upper-floor temperatures by approximately 4°F (2°C), and first-floor temperatures by approximately 2°F (1°C), despite the presence of substantial attic insulation.
Reduced Heat-Related Stress on Roofing Materials
SBS (styrene-butadiene-styrene) modified-bitumen roofing is widely used for low-slope roofing in British Columbia and is commonly installed with a dark-coloured surface. Under strong summer sun, these surfaces can reach high temperatures and undergo repeated cycles of thermal expansion and contraction. Over time, heat exposure can contribute to accelerated ageing and deterioration of SBS roofs, as can exposure to ponding water, a condition that is often excluded from manufacturer warranty coverage.
Benefits to Buildings
Lower Roof Temperatures & Reduced Thermal Stress
By reflecting more solar energy and absorbing less heat, cool roofs can remain substantially cooler than conventional dark roofs during sunny conditions. The U.S. EPA reports that highly reflective and emissive cool roofs can remain approximately 28-33°C cooler during peak summer weather. Lower roof temperatures can also reduce the repeated heating and cooling cycles experienced by roofing materials, potentially reducing thermal stress and contributing to longer service life for some roofing systems.
Improved Indoor Comfort
Reducing the amount of solar heat absorbed at the roof can help limit heat transfer into the building and keep interior spaces cooler during prolonged hot weather. This can be particularly important in buildings without adequate mechanical cooling and in upper-floor spaces immediately below the roof. The benefit varies with insulation, ventilation, building design and other factors, but cool roofing can provide a useful passive contribution to improving indoor comfort during periods of high heat.
Reduced Cooling Demand & Energy Use
By reducing solar heat gain through the roof, cool roofing can reduce the amount of energy required for air conditioning and other mechanical cooling. The resulting savings vary considerably according to climate, building design, insulation, occupancy and roofing system. During periods of extreme heat, reduced cooling requirements can also lower a building’s contribution to peak electricity demand, providing benefits beyond individual energy savings when cooling systems and electrical infrastructure are under their greatest strain.
Compatibility With Rooftop Solar
Cool roofing and rooftop solar can work as complementary building technologies. Lower roof-surface temperatures can improve conditions around photovoltaic equipment, while highly reflective roof surfaces can increase the light reaching the rear of bifacial solar panels designed to generate electricity from both sides. The additional benefit depends on panel type, orientation, mounting height, spacing and roof reflectance, but considering roofing and solar together can improve the overall performance and long-term planning of the rooftop.
Reduced Cooling Demand and Energy Use
Reducing heat gain through the roof can lower the amount of energy required for air conditioning and other forms of mechanical cooling, potentially reducing both cooling costs and peak electricity demand. Research reviewed by the EPA has reported widely varying cooling-energy savings depending on building type, climate and other conditions. One review encompassing more than 25 studies found average cooling-energy savings of approximately 20%. In individual building examples summarized by the EPA, measured cooling-energy savings ranged from 10% to nearly 70%, while reductions in peak cooling demand ranged from 14% to 38%. Actual savings will vary according to factors such as building design, insulation levels, occupancy patterns and the roofing systems being compared.
Compatibility With Rooftop Solar
Cool roofing, achieved either through roof coating or the installation of a new membrane system, can be beneficially combined with rooftop solar as a complementary strategy. By maintaining lower roof-surface temperatures, reflective roofing may modestly reduce heat around rooftop photovoltaic equipment and improve operating conditions. Reflective roof surfaces can also increase the light reaching the rear side of bifacial solar panels, which are designed to generate electricity from both sides, thereby meaningfully increasing their energy yield. This additional generation depends strongly on panel orientation, mounting height, spacing, roof reflectance and local conditions, but the combination provides an additional reason to consider reflective roofing when planning rooftop solar installations.
Benefits to Communities
Reduced Urban Heat
Roofs represent a significant portion of the exposed surface area in developed communities. Conventional dark roofs absorb solar energy and subsequently release heat into their surroundings, contributing to the Urban Heat Island Effect. Cool roofs reflect more solar radiation and absorb substantially less heat. When used across many buildings, lower roof temperatures can help reduce accumulated heat within neighbourhoods and form part of a broader strategy that also includes trees, shade, green infrastructure and other heat-reduction measures.
Support for Extreme-Heat Adaptation
By reducing heat gain within buildings and contributing to cooler urban environments, cool roofing can support broader strategies for adapting communities to increasingly hot summers and more frequent extreme-heat events. It is not a substitute for air conditioning, shade, trees or other heat-protection measures, but provides a passive measure that operates whenever sunlight reaches the roof. Programs such as NYC CoolRoofs demonstrate how reflective roofing can be incorporated into wider municipal heat-resilience initiatives.
Reduced Peak Electricity Demand
During hot weather, widespread air-conditioning use can place substantial demands on electrical systems precisely when communities are experiencing their greatest heat stress. By reducing building cooling requirements, widespread use of cool roofing can help reduce peak electricity demand. This can complement other measures intended to improve energy efficiency and grid resilience while reducing the additional cooling load created when conventional dark roofs absorb solar energy and transfer a portion of that heat into buildings.
Healthier, More Heat-Resilient Communities
Cool roofs are one component of a broader approach to protecting people and buildings from increasing heat. Used alongside air conditioning, insulation, ventilation, trees, shade and other heat-protection measures, they can help reduce indoor heat gain, cooling demand and heat released into developed areas. Collectively, these benefits can contribute to more comfortable buildings, reduced pressure on electrical infrastructure and communities better prepared for prolonged hot weather and extreme-heat events.
How Do Cool Roofing and Insulation Work Together?
A cool roof should not be confused with roof insulation. Insulation slows the transfer of heat through the building enclosure. Cool roofing reduces the amount of solar heat absorbed at the exterior roof surface in the first place.
The two measures can therefore work together rather than representing competing approaches to building performance. A well-insulated building can still benefit from reducing the solar heat absorbed by its roof.
Cool Roofing Is a Passive Technology
One of the defining characteristics of cool roofing is that its heat-reduction effect is passive.
Once installed, the reflective roof surface does not require electricity, mechanical equipment or occupant action to reduce solar heat absorption. Whenever solar radiation reaches the roof, the surface characteristics of the roofing determine how much of that energy is reflected and how much is absorbed.
Cool roofing does not replace air conditioning or other measures needed to protect people during dangerous heat. It does, however, reduce one of the principal ways solar heat is absorbed by buildings and accumulated across developed areas.
Why Cool Roofing Matters in BC
Cool Roofing as a Practical Climate-Adaptation Measure
British Columbia is already experiencing rising average temperatures and more frequent, prolonged and intense periods of extreme heat. The 2021 heat dome demonstrated how quickly extreme heat can become a public-health emergency, compromise building performance and strain critical infrastructure. Preparing for future events requires both effective emergency response and practical measures that reduce heat exposure before dangerous conditions develop.
Cool roofing is one such measure. By reducing the solar energy absorbed at the roof surface, a suitable cool roof can help limit heat gain within a building and reduce the heat subsequently released into the surrounding environment. It is not a substitute for insulation, ventilation, mechanical cooling, shade, trees or other heat-protection measures. Its value lies in providing a durable, passive layer within a broader heat-resilience strategy.
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When Extreme Heat Becomes an Indoor Emergency
Extreme heat is often perceived as an outdoor-weather problem, yet its most serious consequences can occur indoors. The BC Coroners Service identified 619 heat-related deaths in British Columbia during the summer of 2021. Almost all of the fatal heat exposures occurred inside residences, with excessive indoor temperatures identified as the primary cause of injury and death during the extreme-heat event.
This experience demonstrated that building performance — particularly the ability of homes and community facilities to limit heat gain and release accumulated heat — is a matter of public interest. Roofs are not the complete solution, but they are among the building surfaces most directly exposed to summer sun. How they are designed, maintained and renewed should therefore form part of heat-adaptation planning.
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Every Roofing Decision Is a Long-Term Opportunity
Each year, roofs across British Columbia are constructed, replaced, repaired or restored. Decisions made at these points can remain in place for decades. This creates a recurring opportunity to consider solar reflectance and thermal performance alongside waterproofing, durability, appearance, cost and other project requirements.
The objective is not to replace serviceable roofs prematurely or prescribe a single roofing solution for every building. It is to ensure that cool roofing is considered whenever a roofing decision is being made. For some buildings, this may mean selecting a high-performance cool roof for new construction or roof replacement. For others, it may mean determining whether a suitable reflective roof-coating system can restore and extend the service life of an existing roof.
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A Hotter Future Changes What We Need From Our Buildings
BC’s hotter summers and extreme-heat events make building heat resilience increasingly important. The 2021 heat dome showed how dangerous conditions can develop inside buildings. Preparing for future events requires practical measures that reduce heat gain before an emergency occurs.
Cool roofing can contribute by reducing solar heat absorption as part of a broader strategy that includes insulation, ventilation, mechanical cooling, trees and shade.
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When Extreme Heat Becomes an Indoor Health Emergency
The BC Coroners Service identified 619 heat-related deaths during the summer of 2021. Almost all fatal heat exposures occurred inside residences. This makes the ability of buildings to limit heat gain a matter of public interest. Roofs are among the surfaces most directly exposed to summer sun, and their solar performance should form part of heat-adaptation planning.
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Every Roofing Decision Is a Long-Term Opportunity
Roofs constructed, replaced, repaired or restored today can remain in place for decades. Each roofing decision creates an opportunity to consider solar reflectance and thermal performance alongside waterproofing, durability, appearance and cost. The objective is to consider cool roofing when work is already being planned, rather than replacing serviceable roofs prematurely. Suitable reflective coatings may also offer opportunities to restore and extend existing roofs.
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Making Cool Roofing a Routine Consideration
Solar performance should be a routine part of roofing decisions. Clear product information and greater recognition of solar reflectance and SRI would help owners, designers, contractors and public purchasers compare available options. BC’s climates and buildings vary, so suitability and expected benefits should be assessed for the particular climate, building and roof assembly, alongside durability, warranty, cost and other project requirements.
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Reducing Normal and Peak Electricity Demand
Cool roofing can provide buildings with significant annual energy savings by limiting solar heat absorption and reducing building cooling requirements. These benefits become particularly important during summer and extreme heat events, when increased reliance on air conditioning can substantially increase electricity demand. During British Columbia’s 2021 extreme-heat event, BC Hydro reported an approximate 8% demand increase over the previous summer peak record and an increased number of service disruptions.
Cool roofs cannot eliminate peak demand, and their effect varies by building. However, reducing avoidable solar heat gain can complement efficient cooling, heat pumps, insulation, shading and demand-management measures. At scale, passive measures can contribute to a more balanced approach: improving the building first while planning responsibly for the energy needed to keep occupants safe.
More Than Awareness Required
Cool roofing will not become a routine part of roofing decisions in British Columbia through awareness alone. Progress will require coordinated action to make credible information readily accessible, suitable products easier to identify and cool-roofing options more consistently considered.
Increasing awareness of cool roofing is important, but awareness alone will not change the roofs installed on buildings across British Columbia. Cool roofing needs to become one of the options routinely considered when roofs are designed, replaced or restored.
Roofing decisions made today can remain in place for decades. Considering future climate conditions, building performance and heat resilience when those decisions are made can help ensure that opportunities to reduce unnecessary solar heat absorption are not overlooked.
Important enabling steps include:
Providing clear, independent education for building owners, designers, contractors, suppliers and decision-makers
Undertaking British Columbia-based demonstrations and performance monitoring across different building and roofing types
Providing consistent product information based on recognized measures of solar performance
Incorporating cool-roofing considerations into public procurement, extreme-heat planning, building policy and incentive programs; and
Encouraging collaboration among industry, governments, researchers, utilities, community organizations and building owners.
Together, these measures can build confidence in cool roofing without overstating its performance or suggesting that it is appropriate for every building. These measures can also help ensure that roofing investments made today are evaluated against the hotter conditions British Columbia is increasingly expected to experience in the future.
Public Buildings Can Lead
Municipal, provincial and other publicly managed buildings provide an important opportunity to demonstrate leadership in the use of cool roofing. Schools, healthcare facilities, community centres, supportive housing and other public-serving buildings are particularly important because many serve people who may be more vulnerable to extreme heat.
When public agencies consider cool roofing as buildings are constructed, reroofed or restored, they can demonstrate practical application, build local experience, provide visible examples and help establish cool roofing as an option routinely considered throughout the wider community.
By demonstrating cool roofing on the buildings they own and manage, public agencies can help establish greater awareness, confidence and acceptance of cool roofing throughout the communities they serve.
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