High Reflectance Hardscape Materials

What are High Reflectance Hardscape Materials?

High reflectance hardscape materials or “cool” pavements are paving materials with high solar reflectance (albedo), such as concrete, that absorb minimal heat, reducing the heat island effect.^[1] Albedo, or solar reflectance, is the ratio of the amount of light reflected from a surface to the amount of light shining on that surface. Pavements with a lower albedo absorb more sunlight and increase in temperature, while pavements with higher albedo absorb less sunlight, remaining cooler.^[2] The heat island effect refers to the increase in temperature in developed areas that results from heat-absorbing paved areas, the loss of naturally cooling vegetation, and waste heat produced by buildings, motor vehicles, and machinery. This increase in temperature leads to increased energy demands, air conditioning costs, greenhouse gas (GHG) emissions, and pollution while increasing the risk of heat-related illnesses.^[3]  Urban areas exacerbate the heat island effect where 1/3 of surfaces are covered by pavement, particularly dark colored surfaces, which absorb more sunlight than light-colored surfaces and remit heat back in the environment (see Cool Roofs).^[4]

Figure 1 – Concrete pavers (Source: Queens Botanical Garden)

How to Incorporate High Reflectance Materials

High reflective “cool” pavements stay cooler in the sun than traditional pavements. Use reflective aggregate, a reflective or clear binder, or a reflective surface coating to enhance the reflective properties of pavement.^[5] When selecting hardscape materials, consider the albedo (solar reflectance) and solar reflectance index (SRI) of the material. The SRI, which ranges from zero to 100, indicates the effect of a surface’s reflectance and emittance on its surface temperature. Materials with the highest SRI are the coolest. New asphalt pavement has an SRI of 0, while new white Portland cement concrete can have an SRI of between 86 and 100. Emittance, or emissivity, is a range between 0 and 1 that indicates how much heat is emitted by a surface. Since most opaque materials used for paving have an emittance of around .9, the albedo of a material determines its SRI.^[6]

Consider using pavers (concrete masonry units) as an alternative to asphalt and other dark materials for driveways, parking lots, plazas, and streets. Most pavers use high reflectance materials and some pavers also help reduce stormwater runoff by allowing water infiltration (see Pervious Hardscape Materials).^[7]  Check with the manufacturer to find out each product’s specifications. Pavers are available in a wide array of shapes, colors, and sizes.

The natural landscape can help cool a building and the site (including parking lots, streets, and entranceways into the building). For example, using trees and other vegetation to shade paved areas can protect the area from unwanted solar energy. Incorporating trees and plants for shade also decreases surface and air temperature, increases comfort, and connects people to the natural environment (see Biophilic Design and Energy-Efficient Landscaping).^[8]

Examples

New York State Energy and Research Development Authority: Mitigating New York City’s Heat Island with Urban Forestry, Living Roofs, and Light Surfaces

This study used a regional climate model in combination with observed meteorological, satellite, and GIS data to determine the impact of urban forestry, living (green) roofs, and light-colored surfaces on near-surface air temperature and the urban heat island effect in New York City. Findings showed that among the single-strategy scenarios, light surfaces, light roofs, and living roofs can potentially reduce the summer peak electric load more than the other strategies.

Urban Heat Island and Climate Change: An Assessment of Interacting and Possible Adaptations in the Camden, New Jersey Region

This research project focused on the analysis of the urban heat island effect in the greater Camden region and on mitigation strategies for the urban heat island in the city of Camden and adjoining communities. Mitigation strategies for the urban heat island effect included increased urban vegetation and lighter-colored surfacing.

Benefits

• Reduces energy demand and lowers utility costs.
• Improves water quality by reducing the surface temperature of stormwater runoff and protecting aquatic life.^[9]
• Improves air quality, as decreased energy demand results in decreased air pollution and greenhouse gas emissions.
• Improves aesthetics with an increase of trees and vegetation along with a reduction of large paved spaces.
• Improves health and comfort by reducing the heat island effect.^[10]
• Increases the solar reflectance of roads, enhancing road visibility and reducing the electricity required for street lighting at night.

Costs

The cost of any pavement application varies by region, the contractor, the time of year, materials, accessibility of the site, local availability of materials, underlying soils, size of the project, expected traffic, and the desired life of the pavement. Although the cost of these materials varies based on the factors listed above, an estimated cost range for a standard concrete installation is $4.00–$5.00/square foot, while a standard asphalt installation costs $3.00–$3.25/square foot.^[11] However, concrete has an estimated service of 15-35 years, while conventional asphalt’s service life is about 7-20 years.^[12]  High reflectance concrete pavers are comparable in price to darker colored concrete pavers. For cost information for shading (see Tree Protection and Placement).

There are also cost savings associated with mitigating the urban heat island effect. For every 1°F increase in air temperature, electricity demand for cooling grows by 1.5-2%.^[13] Densely populated urban areas are often 2 to 9 degrees Fahrenheit higher than surrounding suburban and undeveloped areas; this translates to an increase in cooling demand ranging between 3.5-15.75%.^[14] Project teams that want to use high reflectance pavements as part of a heat island mitigation program may find it hard to estimate the net costs or benefits based on temperature reduction alone. The highest overall value may result when multiple benefits, such as improved stormwater management and water quality, are also factored into the evaluation of a paving project. For more in-depth cost-benefit analysis of various urban heat island mitigation scenarios using high reflectance hardscape materials and shading see Section 6 of the New York State Energy and Research Development Authority’s Mitigating New York City’s Heat Island with Urban Forestry, Living Roofs, and Light Surfaces.

Resiliency

High reflectance hardscape materials contribute to resiliency through their reduction of the heat island effect, especially during severe heat waves or power outages, when vulnerable populations are at risk from heat-related illnesses, and air-conditioning demands put additional stress on an outdated and overtaxed electricity grid.

^[1] Portland Cement Association. “Heat Island Reduction.” http://www.concretethinker.com/solutions/Heat-Island-Reduction.aspx (accessed March 22, 2018).

^[2] Lawrence Berkeley National Laboratory Heat Island Group. “Cool Pavements.” https://heatisland.lbl.gov/coolscience/cool-pavements  (accessed March 22, 2018).

^[3] NJ DEP. “Urban Heat Island and Climate Change: An Assessment of Interacting and Possible Adaptations in the Camden, New Jersey Region.” http://www.state.nj.us/dep/dsr/research/urbanheat.pdf (accessed March 22, 2018).

^[4] Berkeley Labs. Cool Pavements. https://heatisland.lbl.gov/coolscience/cool-pavements (accessed May 14, 2018).

^[5] Berkeley Labs. Cool Pavements. https://heatisland.lbl.gov/coolscience/cool-pavements (accessed May 14, 2018).

^[6] Portland Cement Association. “Heat Island Reduction.” http://www.concretethinker.com/solutions/Heat-Island-Reduction.aspx (accessed March 22, 2018).

^[7] Portland Cement Association. “Hardscape & Pavers – Permeable Pavement and Surfaces.” http://www.concretethinker.com/applications/Hardscape-Pavers.aspx  (accessed March 22, 2018).

^[8] US EPA. “Heat Island Effect: Using Trees and Vegetation to Reduce Heat Islands.” https://www.epa.gov/heat-islands/using-trees-and-vegetation-reduce-heat-islands  (accessed March 22, 2018).

^[9] US EPA. “Heat Island Impacts.” https://www.epa.gov/heat-islands/heat-island-impacts  (accessed March 22, 2018).

^[10] US EPA.  “Climate Change Indicators in the United States: Heat-Related Deaths.” Updated August 2016 https://www.epa.gov/sites/production/files/2016-08/documents/print_heat-deaths-2016.pdf  pg. 1 (accessed March 22, 2018).

^[11] Costs provided by two of the significant asphalt and concrete suppliers in NJ (May 14, 2018).

^[12] US EPA. “Reducing Urban Heat Islands: Compendium of Strategies: Cool Pavements,” https://www.epa.gov/sites/production/files/2017-05/documents/reducing_urban_heat_islands_ch_5.pdf. (accessed March 22, 2018)

^[13] US EPA. “Heat Island Impacts.” https://www.epa.gov/heat-islands/heat-island-impacts (accessed March 22, 2018).

^[14] Rutgers Center for Green Building. “CAP Project.” http://rcgb.rutgers.edu/ (accessed March 22, 2018).