Re-roofing your home can be one of the most costly renovation projects you can undertake. Your roofing material is highly visible, it takes a beating from the elements, and it is partially responsible for your home's heat loss and gain. So choosing a durable, energy-efficient material should be high on your priority list.
But the question of sustainability is another matter, and almost no roofing material qualifies as truly sustainable. If your picture of a sustainable roof is limited to a green or living roof, you may be surprised to learn that sustainability is a broad category that can include many types of roofing materials.
Environmental Performance Factors
What makes a roofing material green, or environmentally friendly, is not just the raw materials it comes from and how it is manufactured; it's also how the roof performs over its lifetime and how the roofing is disposed of at the end of its life.
The key performance factors are overall durability and the material's resistance to heat gain, which can affect the cost of cooling the home. The Energy Star program certifies a number of roofing materials for relatively high heat reflectivity, or their ability to reflect heat away from the roof, thus lowering cooling costs. Energy Star certification is not limited to specific roofing materials.
What Makes Roofing Sustainable?
The question of sustainability is more about the raw material than any other factor. By definition, a sustainable material is produced without depleting or permanently damaging its resource. Many environmental experts also would include the requirement that sourcing the material does not cause significant or irreparable damage to the earth. By these definitions, any roofing material that uses fossil fuels or mined materials is not sustainable because both come from an irreplaceable resource.
Comparing Roofing Material Sustainability
Although metal roofs are energy-intensive to produce, they are attractive and long-lasting, and they often contain high recycled content or are easily recyclable at the end of their lifetime. Metal roofs can reflect some heat to reduce heat gain, but they must be insulated properly because the metal is highly conductive of heat. The most common metal roofing materials are steel and aluminum. Metals are made with materials mined from the earth and therefore are not technically sustainable.
Beautiful and incredibly durable (a slate roof can outlast a house), slate is also very expensive and heavy, and it takes significant resources to mine it, process it, and transport it. Most slate in the U.S. comes from the Northeast. Mining stone is not a sustainable practice. Also, the weight of slate roofing necessitates extra roof framing, which uses additional resources not required with lighter-weight roofing materials.
Clay Tile Roofs
Also known as terra cotta, clay tiles are also extremely durable as well as heavy and expensive. Authentic clay tiles are made with natural clay that is shaped and fired, similar to ceramic tile. Some tiles receive special glazes or paints for color or other added properties. The clay used for tiles is such a plentiful resource that many clay tile manufacturers claim their products to be sustainable.
Wood Shakes and Shingles
Wood shakes and shingles are arguably the most, and perhaps only, sustainable roofing materials because wood is a sustainable resource. Of course, that assumes the roofing comes from sustainably harvested sources. Shakes and shingles are fairly energy-intensive to produce and are only moderately durable—much less so than slate and clay tile.
Disposal of wood roofing is easy because it is a biodegradable material, provided it has not been treated with synthetic additives or preservatives. Wood can be an especially sustainable choice if you live in an area that produces shakes locally, and/or you have access to shingle made from FSC certified wood.
Technically called composite shingles, standard asphalt shingles are moderately durable and can offer good heat reflectivity, depending on the shingle design and color. They are made with paper, and minerals as well as fiberglass, tar, and other petroleum products. Some companies and municipalities make use of discarded asphalt shingles, but for the most part, old shingles are not widely recycled and are not biodegradable. As a petroleum-based product, they are not sustainable.
Concrete Tile and Fiber-Cement Roofing
Both concrete roofing tile and fiber-cement shingles are made with Portland cement, which is highly energy-intensive to produce. It also creates a significant amount of CO2 emissions (a greenhouse gas). However, these roofing materials are extremely durable. Concrete tiles are heavy and may require additional roof framing. They are also quite fragile and should not be walked on. Fiber-cement shingles can look similar to slate but are much lighter in weight.
Green Roof Systems
Also known as living roofs, green roofs are flat or low-slope roofs that are partially or completely covered by vegetation, either in the form of grass or other small plants, preferably species native to the local area. Green roofs also include a growing medium (typically soil and inorganic materials) and a synthetic waterproof membrane.
Although green roofs can be high-maintenance and expensive to install, they offer several benefits, including the absorption of rainwater to prevent runoff and providing insulation for your home. In urban areas, green roofs help to reduce the heat island effect, accumulated heat from concrete, asphalt, and other building materials.
On the downside, green roofs rely on a heavy-duty rubber membrane to waterproof the roof. This is made of petroleum, which is not a sustainable resource. Green roofs also are very heavy and require additional roof framing for support.
Tips for Choosing Sustainable Roofing Materials
- Recycled Content. Check to see if the roofing material contains recycled content. Generally, the higher the percentage the better, although durability wins out in the end. Also, confirm that the material can be recycled again at the end of the roof's lifetime.
- Coatings. Avoid copper and zinc-coated roofing materials, which can wash into water sources and are dangerous to aquatic life.
- Maintenance. No one wants to spend a lot of time or money maintaining their roof every year. Be sure your roofing material is durable and that no toxic products are required to maintain it.
- Weight. In theory, it might seem like the heaviest roof would be the best, being both highly durable and unlikely to tear away in high winds. However, you must be sure that your home's existing structure can support the weight of new roofing material.
- Roof slope. Is your roof nearly flat, low-slope, or high-slope? Some roofing materials perform much better than others, depending on the application.
- Color and reflectivity. If you live in a particularly hot climate, look for roofing materials that are light in color and have high reflectivity. They will bounce more of the sun rays rather than heating your home like an oven.
- Warranty. Select roofing materials with the longest warranty possible, as this is a good indication of quality and durability.