Cool Metal Roofing

Defining Cool Roofing

Cool roofing is defined differently by various performance criteria in codes, standards, and incentive programs. In general, a cool roof is one that has relatively high solar reflectance and high thermal emittance.

Defining-Cool-Roofing

During the daylight hours, a roof is constantly subjected to solar energy striking its surface. The term “Solar Reflectance” is a measure of the amount of that solar energy that is immediately reflected from the surface. It is not reflected heat but reflected electromagnetic energy from the sun. Solar reflectance is reported as a decimal (0 – 1.00) or as a percentage (0-100%). The solar energy that is not reflected away from the surface is absorbed into the outer surface of the roof product and is converted into heat. The heat can be removed by convection as air flows over the surface or by conduction through the roof material into the sheathing below. The energy that is left can also be re-emitted to the night sky in the form of infrared energy. That re-emitted energy is referred to as thermal emittance, which is also expressed as a decimal (0 – 1.00) or as a percentage (0-100%).

A cool metal roof with high solar reflectance and high thermal emittance would have a lower surface temperature as compared to a roof with low reflectance and low emittance. In the case of a cool metal roof, a lower surface temperature translates into less heat gain into the attic space or living space below the roof. The result is a cooler living space and lower cooling/heating energy consumption.

Studies have shown that a cool metal roof can save a building owner as much as 20% in their cooling energy costs. In addition, by reducing energy production at the power plants, greenhouse gases that are emitted in the production process are thereby reduced. Many metal roofing systems meet other cool roof requirements in codes and standards.

Cool Roofing

Cool Metal roofing utilizes reflective pigments to reflect the sun's energy away the roof. Cool roofs help reduce energy consumption and also reduce urban heat island effects. Standard industry criteria for cool roofs are:

For steep slope applications (greater than 2:12 pitch): initial minimum solar reflectance of 0.25, and 3-year aged minimum solar reflectance of 0.15.

For low slope applications (2:12 or less pitch): initial minimum solar reflectance of 0.65 and 3-year aged minimum solar reflectance of 0.50.

Solar Reflectance, Thermal Emittance, and SRI Values for Kynar 500 Colors
COLOR	REFLECTANCE	EMISSIVITY	SRI
Almond - PVDF	.60	.84	70
Ash Gray - PVDF	.39	.84	32
Autumn Red - PVDF	.31	.85	35
Bone White - PVDF	.71	.85	86
Brandywine - PVDF	.26	.85	24
Brite Red - PVDF	.42	.84	45
Buckskin - PVDF	.38	.86	41
Champagne Metallic - PVDF	.38	.80	38
Charcoal - PVDF	.32	.85	32
Clay - PVDF	.32	.86	33
Colonial Red - PVDF	.33	.85	34
Copper Penny Metallic - PVDF	.49	.85	55
Dark Bronze - PVDF	.26	.84	24
Evergreen - PVDF	.26	.84	24
Galvalume Plus	.69	.19	62
Hartford Green - PVDF	.25	.85	23
Ivory - PVDF	.67	.87	81
Leadcoat - PVDF	.37	.82	38
Light Stone - PVDF	.53	.86	61
Mansard Brown - PVDF	.30	.85	30
Matte Black - PVDF	.27	.86	26
Medium Bronze - PVDF	.30	.87	31
Patina Green - PVDF	.46	.85	51
Patrician Bronze - PVDF	.27	.86	26
Preweathered Galvalume - PVDF	.30	.79	27
Regal Blue - PVDF	.26	.85	24
Regal White - PVDF	.68	.86	82
Roman Blue - PVDF	.26	.85	24
Sandstone - PVDF	.54	.86	63
Silver Metallic - PVDF	.57	.78	64
Slate Gray - PVDF	.43	.85	47
Surrey Beige - PVDF	.40	.86	43
Terra Cotta - PVDF	.35	.85	36
Terratone - PVDF	.33	.86	34
Texas Silver Metallic - PVDF	.58	.78	57
Tudor Brown - PVDF	.29	.86	29

Solar Reflectence, Thermal Emittance, and SRI Values for Silicone Modified Polyester (SMP) Colors
COLOR	REFLECTANCE	EMISSIVITY	SRI
Alamo White	.64	.86	77
Antique Brown	.28	.86	27
Ash Gray	.46	.86	52
Autumn Red	.35	.86	37
Brandywine	.33	.87	35
Brite White	.66	.87	80
Charcoal	.37	.86	39
Clay	.42	.86	46
Evergreen	.29	.86	29
Ivory - Galvalume Substrate	.69	.87	84
Light Stone	.56	.86	65
Mansard Brown	.31	.86	31
Matte Black	.31	.86	31
Patrician Bronze	.30	.87	31
Pewter Gray	.46	.86	52
Roman Blue	.32	.86	33
Surrey Beige	.46	.87	52
Terratone	.31	.86	31
Timber Tan	.47	.86	53
Tudor Brown	.33	.86	34


MET-TILE COLOR	REFLECTANCE	EMISSIVITY	SRI
Bravo Red	.46	.86	52
Cotillion White	.67	.86	81
Coral Blue	.27	.87	27
Gallery Blue	.30	.85	30
Meadow Green	.28	.85	27
Mission Clay	.36	.87	39
Morocco Red	.27	.86	26
Ranchwood Brown	.29	.83	27
Slate Gray	.26	.85	24
Spanish Tile Red	.35	.86	37


MILAN TILE COLOR	REFLECTANCE	EMISSIVITY	SRI
Adobe Red	.32	.87	33
Blue Slate	.32	.89	34
Cedar Shake	.31	.87	32
Classic Cedar	.26	.87	28
Ebony	.27	.84	25
Gray Slate	.32	.89	34
Green Slate	.32	.89	34
Heritage Green	.25	.87	24
Homestead Brown	.25	.83	23
Keystone Gray	.32	.87	33
Linen	.51	.88	59
Manor Gray	.25	.87	24
New Penny	.41	.86	45
Red Slate	.32	.89	34
Seasoned Cedar Shake	.27	.88	27