Green Building Elements

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At some point in the useful life of most houses, the roof needs to be replaced. An EPA report prepared in the late 1990s calculated that almost 4 million homes per year have their asphalt roofs replaced, leading to the generation of 6.4 million tons of asphalt roofing waste. (Table A-8) Because of this, roofing materials are one of the larger contributors to landfill construction debris. And most of the materials used in making shingles (the prevalent form of roofing used in North America) are not readily recycled into other useful forms, leading to a stream of materials filling up the landfills.

Roofs are subject to extremes of temperature, receiving the full exposure of the sun as well as suffering from the extremes of cold. No other part of the average home sees a wider cycle of temperatures. Precipitation and wind also provide a constant eroding force that wears at the roof and gradually contributes to breaking it down. Because of this exposure to the elements, roofs are typically elements that need to be replaced several times over the life of a building.

Are there greener options than a basic shingle replacement?

Shingle Roofs are still the most prevalent form of roofing in the United States. Either organic (which, in this context, doesn’t mean what you might otherwise think) or fiberglass shingles are mats of material with small mineral granules adhered to them. The granules are the weathering layer, but as they become detached over time, the body of the shingle becomes susceptible to water and ultraviolet damage, leading to leaks and other roofing problems. The hotter the climate, the shorter the typical lifespan of a shingle. Although manufacturers promise 20 and 30 year warranties on their materials, those are pro-rated by the length of time the shingles have been in place. And much of the cost of installation, repair, and replacement is in the labor, rather than the cost of the materials.

Vegetated Roofs are becoming increasingly popular in new construction, and many LEED certified buildings have used green roofs for the wide range of benefits they provide. Can I put a vegetated roof on my house? Unless you are really attached to the idea regardless of cost or obstacles, probably not. There are a few considerations that make it difficult to install a green roof on an existing building, whether it is a house or a commercial building. First of all, vegetated roofs are still rather expensive, which usually ends the discussion right away. Green roofs are also heavier than most other roofs, and structural reinforcement would typically be necessary in order to put the underlayment materials, growth media (the soil) and the plants all onto an existing roof. Furthermore, a vegetated roof can typically only be installed on a fairly low slope roof (though there are ways of adding structures that can hold a vegetated roof on a steeper slope, but those add further weight and cost) and most homes have steeper roofs. However, the aesthetics of a green roof are undoubtedly appealing, and the availability of materials for installing residential green roofs is becoming more common.

Metal Roofs are another option that can be considered. Metal roofs are far more durable than shingles. While a shingle roof may have a lifespan of up to 20-30 years, a metal roof should last at least twice as long. And even if the material for a metal roof costs three times as much as a shingle roof, by avoiding the cost of removing the old roof, buying new roof material, and installing the new roof when the shingle roof has worn out, the metal roof avoids that additional labor and material waste. Furthermore, at the end of its life, a metal roof can be usefully recycled. The biggest drawback to metal roofs is the relatively high embodied energy in refining and manufacturing metal, but the long life and recyclability of the material helps to balance that out.

Slate and Tile Roofs are very durable materials. Slate has been used for centuries, and slate roofs can, in some cases, last for many hundreds of years. Installation is expensive and labor intensive. Slate and tile are also heavy materials, an, as is the case with a vegetated roof, additional structural support may be needed in order to accommodate the weight. However, slate roofs are also some of the most durable, with buildings still standing with hundreds of years’ old slate roofs still on them. For most residential uses, the cost of such a roof (especially as a retrofit onto an existing home) is prohibitively expensive. The materials used to make these are fairly low impact: either slate, which is a natural stone that is split into thin pieces to be used for roofing, or clay tile, which uses an abundant material although it requires kiln firing in its manufacture. Both are relatively low embodied energy choices and are probably the most environmentally benign.

Wood Shake Roofs are popular in some parts of the country. The recent wildfires around San Diego demonstrate one of the main drawbacks to shake roofs - they are flammable. Wood roofs are most popular in areas that do not receive a lot of rain, but the constant exposure to the sun can lead to failure of these materials over time. Synthetic materials, which are much more flame resistant, are taking over in instances were wood shakes were once used.

Life-cycle considerations are what is at issue here. Most Americans don’t expect to be in a home for so long that a more expensive roof would pay for itself, so they opt for the less expensive shingle roof. Homebuyers don’t see the additional value of a longer lifespan roof and may be afraid of higher maintenance costs for having such a roof. While it would be likely that similar levels of repair work would be more expensive on other types of roofs than on shingle roofs, the fact that those repairs are much less common doesn’t necessarily register.

Looking at not just the initial installation cost, but rather the whole life cost (how much it costs divided by how many years of useful life it can be expected to provide) can help in evaluating the life-cycle cost of different choices. The cost of the materials and labor, as well as the impact of the production of those materials all contributes to the overall impact of a new roof. Weighing those factors and taking into account regionally appropriate design will lead to finding the greener roof replacement options for you.

Links: US EPA Report (PDF)

Shinglelife

Metal Roofing Questions

Roofscapes

image source: EcoGeek.org