When it comes to making a home energy-efficient, the choice of roof can have a far-reaching impact on the overall sustainability of a structure. The right kind of roof makes a home’s entire energy infrastructure operate more efficiently, staying naturally warm in winter and cool in summer. This cuts down the need to augment temperature through heating or air conditioning and reduces reliance on the earth’s natural resources.
Two kinds of roofing are mentioned most often as green alternatives: metal roofing with solar reflective coating (“cool metal roofing”) and vegetative roofing.
Cool metal roofing is a family of sustainable, energy-efficient roofing products available in a wide variety of finishes, colors, textures, and profiles for steep-slope and low-slope applications.
Vegetative roofing involves literally growing plants on the roof. It can only be done on low-slope (flat) roofs.
Metal roofs with a solar reflective coating and vegetative roofs both reduce health hazards due to excessive heat in cities. Both can reduce electricity consumption, especially during the warmer months.
So, which makes the most sense for the average home? Let’s take a closer look.
Cool metal roofing is highly reflective, meets EPA Energy Star performance criteria, and can save 25% on annual energy costs. Emissivity (the amount of heat released) as high as 90% can be achieved for painted and granular-coated metal roofing. Plus, painted metal roofs retain 95% of their initial reflectance and emittance over time.
Metal roofs typically have a minimum recycled content of 25% and are 100% recyclable at the end of a long, useful life.
Cool metal roofing is durable, lasting up to 60 years with minimal maintenance, and is documented to resist wind, hail, fire, and earthquakes. Due to its credible long life and documented durability, metal roofing makes an attractive investment.
Vegetative roofs require significantly more structural support due to the weight of soil, vegetation, retained water, and related materials. Maintenance costs are higher, and vegetative roofs are more labor intensive and expensive after installation because the plants require watering, fertilizing, and other care.
There can be additional costs for water treatment since fertilizer is used, and landscaping may need to be adjusted for the seasons.
Leaks are a concern, sometimes due to the plants’ root systems penetrating a water-barrier membrane. On top of the typical problems associated with roof leaks, this type of leakage can also lead to costly structural issues.
Vegetative roofing does excel at slowing the release of storm water runoff, which can help prevent flooding in urban centers.
Installation for a cool metal roof, including material and labor, runs anywhere from $5 to $20 per square foot. Vegetative roofs double that cost to $10 to $40 per square foot. The cost for vegetative roofs is higher because of the need for additional structural support.
“Affordable Smart Roof Cost/Benefit, Report Summary – 02/2015” by the JPB Foundation, written by Greg Kats and Keith Glasbrook, studied the cost/benefit of roofing options in several cities. The study concluded that cool metal roofing had the best benefit-to-cost comparison. The main driver was the considerably higher cost of installing and maintaining vegetative roofing.
Vegetative roofs can be beneficial with great aesthetics, if maintained properly. However, an inadequately maintained vegetative roof can be an eyesore. With many style, texture, and color options, cool metal roofs can be aesthetically pleasing without the high maintenance and installation costs of vegetative roofs.
Cool metal roofing has a lower overall installation cost, requires little maintenance, and is not vulnerable to leaks. Factor in its durability, 25% reduction in energy bills, and 100% recyclability, and it is the clear choice for worry-free green roofing.