It’s Earth Day and we’re asking “What’s the most sustainable type of roof?”
Roofing, like most industries, has become more sustainable, but it does have a long way to go.
Here are the questions we will ask when considering the characteristics of a sustainable roof:
1) Does the existing roof have to be torn off and disposed of in a landfill?
2) Are they made of highly reflective material that helps reduce energy costs?
3) How toxic are the materials it is made of?
4) Is the material recyclable?
5) How heavy is the material?
6) How long does the roof last?
Slate tiles are heavy, extremely durable and aesthetically pleasing.
Clay tiles are common in California’s central valley.
Slate and Clay Tile
They are the most sustainable roofs of all, due to durability and material content.
- Tile or slate roofs are usually the only roofs that are applied. If a piece is broken, it can be easily replaced.
- Neither are reflective or re-known for reducing energy costs.
- Made from rock or clay, neither have toxic residue and cannot be recycled. They are both heavy.
- Slate is heavy, so is tile. Because the material is heavy, another roof can’t be put on top of it. However, broken tiles can be easily replaced.
- These roofs last longer than any other roof. Concrete tile lasts 50 years. Clay tiles and slate can last 100 years.
Metal roof with acrylic coating, Santa Rosa.
Of all modern roofs, acrylic and silicone roof coatings are the most sustainable.
- They can be applied over the top of an existing roof, eliminating the need for tear-off. The elimination of labor, gas, and dump fees also provides substantial savings to the customer.
- These highly reflective coatings reflect 97-99% of sunlight. This greatly reduces energy costs primarily from air conditioning.
- Coatings are water-based and non-toxic. There is no off-gassing of toxic fumes. This minimizes business disruptions.
- The material is not recyclable and is among the lightest of roofing materials.
- Roof coating lasts 15-20 years. After that, layers of coating can be added, theoretically extending the life of the roof indefinitely.
Rapid-lock TPO roof, Sutter Health in Novato.
- Previous roofs, often asphalt, are torn off to minimize weight on the roof.
- Most TPO is white or grey. Their high reflectivity greatly reduces energy costs.
- Although they are made of plastic, they are stable and non-toxic. They have no off-gassing from toxic materials.
- Some manufacturers claim their TPO material is 100% recyclable. Although this may be theoretically true, it is not practical. We know of no instance in which a TPO roof has been recycled.
- TPO roofs, especially modern formulations can last 20 years, making them one of the more durable roofs. Additionally, they are prime candidates (pun intended) for roof coating, which could extend roof life indefinitely.
Other roof types we won’t be able to cover in detail today, due to time constraints.
Metal roofs are durable and prime candidates for a roof coating to increase life expectancy. They tend to get quite hot unless a reflective coating is placed on them. Tear off is not usually required. They last 40-70 years making them exceptionally durable.
Living Roof at The California Academy of Sciences, San Francisco.
All living roofs have materials underneath them. They are relatively cool and provide exceptional beauty. Often they are living gardens, like those at the California Academy of Science. Accumulated greywater is used to water the roofs, but they may require additional watering.
This durable roof type is relatively expensive, however, it is highly durable. It is a prime candidate for roof coating which can extend its roof life indefinitely. It shares many of the characteristics of TPO roofs and can last 25 years or more.
Asphalt Built-up or Asphalt Shingle
These cost-effective roofs are some of the least sustainable. They inevitably end up in a landfill, although they can potentially be covered with a coating. Made from oil products, they are most often have noxious odors when installed. They also have poor reflectivity and are not energy efficient. They usually last 15-20 years.
A Few Worthy Mentions of Sustainable, Non-Commercial Roofing Solutions
Although it is not particularly durable, it is the only biodegradable roof we know of. Thermal insulation is poor, but unnecessary in climates where it is commonly found. It is extremely renewable, as it is composed of plant material. No toxins are contained in the building material.
The Pueblo at Taos Mexico is a thousand years old. Its roof is made of mud and straw and has excellent thermal insulation. There are no known toxins in the material. The material is 100% recyclable.
In conclusion, roofs continue to evolve. Roofs are a key part of life on planet Earth. Roofing technology has evolved over the millennia. Our stone age ancestors used thatch. Civilization saw the advent of slate, clay tile and adobe. The past 60 years has seen the rise of PVC, TPO and roof coatings. Now we have living roofs that are gardens.
Where will they go from here? We can’t wait to see.