7 types of green roofing

If you own a home with a slate roof, you may not have to think about new roofing for a long while. Slate, one of several natural green roofing options, can last a century. By virtue of its longevity, it's considered one of the most eco-friendly roof materials, as well as an aesthetically pleasing one.

On the other hand, if you have a three-tab asphalt shingle roof, the most popular U.S. roofing choice because of its up-front affordability, expect to replace it about four or five times as often as slate -- approximately every 20 years. When you consider how often it needs repairs and its comparatively short life span, it's not quite as much of a bargain as it seems. As green roofing options go, asphalt roofing shingles don't make the grade. Manufactured from petroleum, they outgas VOCs when new and go to landfills when they're replaced.

In between those two vastly different roofing choices, however, you can find quite a few eco-friendly roof materials -- some old standbys, like slate and wood, are made by nature and we've also included some synthetic look-a likes. Aesthetics and price certainly figure into your decision, but if you really want to choose one of the best green roofing options, you have to know how much CO₂ it emits and how much energy it consumes during the four stages of its life cycle:

1. Sourcing. Consider the raw materials. Are they replenished easily or are they depleted without regard for future resources or for the local environment (as in the case of quarrying, for example)? Are they recycled materials? Are they sourced locally or transported long distances to the manufacturing site?
2. Manufacturing. How much energy does the process and transport to distribution facilities use? How much water does manufacturing use or conserve?
3. In service on the roof. The longer the life expectancy of new roofing, the less often it needs to be replaced. Greater longevity means less resources wasted over time. Is the material energy efficient? The Cool Roofing Rating Council (CRRC) tests and rates new roofing products for thermal emittance and solar reflectance, properties which indicate how effectively the roof stays cool and insulates your home, both of which conserve energy for heating and cooling. CRRC makes their test results and ratings available to manufacturers, who in turn can provide them to consumers. Cool roofing coatings may be added to roofing products to enhance their energy efficiency.
   
4. End of life. Is the material salvageable or recycleable? Some of the best green roofing options end their useful years recycled into new products, not dumped in landfills.

Serious green roofing shoppers may also want to take into account whether a product poses health risks.

Fortunately, you can find many materials that are moderately priced and qualify as sustainable. Given the above considerations, which are the most eco-friendly roof materials? Here's how both traditional and newer synthetic and composite materials compare.

Naturally eco-friendly roof materials

Slate

Green benefits:

• 100-year life expectancy
• salvageable for new roofing or to repurpose as flooring and counters
• minimally processed and kind to the environment
• poses no known health risks

Natural slate, however, has some notable environmental disadvantages:

• consumes more transportation energy than lighter-weight materials
• as much as 15 percent breakage waste from installation
• detrimental effects to local ecosystems from quarrying

Clay and concrete tile

Green benefits:

• 75- to 100-year or more life expectancy
• abundant, mineral-based, recyclable natural resource
• non-toxic for capturing rainwater
• excellent heat-management properties for reduced heating/cooling energy consumption
• modern, environmentally conscious production methods ensure sustainability

Possible environmental disadvantages include:

• due to weight of product, consumes more energy to transport long-distance
• concrete tiles contain cement, which requires an energy-intensive process to manufacture

Wood shingles and shakes

Green benefits:

• 20- to 60-year life expectancy, depending on local conditions and maintenance
• Forest Stewardship Council (FSC)-certified product guarantees sustainability
• processing requires minimal use of fossil fuels
• low overall environmental impact; compostable

Some wood shingles and shakes have these environmental disadvantages:

• required treatment with preservatives or fire-retardants in some locales can leach into waterways
• premium grades may come from old-growth forests not managed sustainably

Metal roofs

Green benefits:

• 40-year or more life expectancy
• recyclable, and/or made from recycled materials
• lightest weight material means low transport energy consumption

Various coatings over metal provide additional eco-friendly benefits:

• superior energy efficiency
• reduction in urban heat island effect
• less chemical pollutants in rainwater runoff

Manmade green roofing options

Designed to closely resemble natural, traditional roofing, these alternatives are sustainable without most of the originals' disadvantages, including higher costs. Here's how their green benefits compare:

Manufactured slate

The lighter weight of manufactured slate tiles requires less transportation energy than natural slate. No quarrying is involved. They install without the waste from easily broken, natural slate tiles. These products have 50-year warranties and all are recyclable.

• Synthetic polymer slate by DaVinci Roofscapes. Made with virgin resins for sustainability, this product is available with cool roof coatings for greater emissivity.
• EcoStar sustainable synthetic slate tiles. These tiles are made from 80 percent recycled rubber and plastic.
• Ply Gem engineered slate. A low heat process fuses polymers with almost 100 percent recycled materials, including real slate.

Composite wood shakes

Similar to manufactured slate products by EcoStar and DaVinci Roofscapes, synthetic wood shakes are made from either virgin resins or recycled materials and polymers. Most have a 40 to 50-year life expectancy, more than some natural wood shakes that succumb much sooner to harsh climates. These roofing materials do not deplete limited forest resources.

Metal shakes, slate, and tiles

Metal roofing can be fashioned to mimic any type of natural roofing product. Metal's natural energy efficiency can be further enhanced by the addition of coatings such as Gerard's Stone-Coated steel roofing products that reduce heat transfer.

In addition to the green benefits of these roofing materials, look for products that also withstand particular regional stress factors such as high winds or wildfire threats.