Which is greener: fiber-cement or vinyl siding?


Which is greener: fiber-cement or vinyl siding?

Asked by Patty Boyce, Berea, KY

We are beginning construction of a new home and making every effort to go green as we proceed. We would like to use HardiePlank fiber-cement siding. Our builder prefers vinyl. He questions our claim that our choice is greener given the environmental costs of cement production. Can you shed some light on this?

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Connie McCullah's picture

If you are choosing between vinyl and fiber-cement siding based on their green qualities, I would recommend you use fiber cement. Your builder is probably referring to the high levels of carbon dioxide?a greenhouse gas?released in cement production. However, the manufacture of the PVC (polyvinyl chloride) used in vinyl siding also involves carbon dioxide emissions because a large amount of electricity is needed to power the process. PVC manufacture may result in twice the carbon dioxide emissions of cement manufacture.

On top of that, vinyl siding creates hazardous and persistent toxins throughout every stage of its life cycle, while fiber cement is inert. It is safer on your house, and safer after you?ve disposed of it. I recommend you go with the fiber cement, and when you order it from the company, tell them you'd like them to set up a program to keep it from going to a landfill one day.

Green buyer's guide: vinyl vs fiber-cement siding

Vinyl Siding Fiber-Cement Siding
Contents About 80 percent PVC (polyvinyl chloride); 20 percent other ingredients. About 45 percent portland cement, 45 percent silica sand, and 10 percent wood fiber.
The manufacture of PVC creates dioxin. While the amount of dioxin released by the PVC industry is small, some studies point to health effects even at low levels.

The production of PVC also creates nitrogen oxide, a greenhouse gas, and sulfur dioxide, which leads to acid rain and smog.

The petrochemicals used to make PVC are captured during the processing of oil.
Producing portland cement involves the decarbonization of limestone, which releases carbon dioxide, a greenhouse gas. However, carbon dioxide emissions from power plants generating the electricity for PVC production may be the same or greater.

Processing plants using sulfur-containing fuel emit sulfur dioxide, which leads to acid rain and smog. Cement production also requires large amounts of water.
Worker Health Due to concerns about vinyl chloride and other toxins in the PVC manufacturing process, the Occupational Safety and Health Administration imposes strict workplace exposure limits. Fiber-cement siding releases silica dust when it is cut. Silica dust is extremely fine and can lead to respiratory problems if inhaled. These health issues can be avoided by using the proper cutting technique and wearing a respirator.
Occupant Health House fires are an acute concern, as the burning of PVC produces both dioxin and polychlorinated biphenyls (PCBs), creating significant health risks. When vinyl siding becomes brittle with age, it releases chemicals into the air, including dioxin and formaldehyde. Fiber-cement siding is non-combustible. It is inert and will not emit fine dust or volatile organic compounds after installation.
Embodied Energy
(The amount of energy
used in a product's life
cycle, including resource extraction, manufacture
and transport)
On a 50-year life cycle, the embodied energy required to clad a house in vinyl is 93,210 megajoules. (For comparison, cedar cladding has an embodied energy of 28,120 megajoules.) Given that cement has five times the embodied energy of wood, and that fiber-cement siding is about half cement, I estimate that the embodied energy in the cement required to clad a house with fiber-cement siding would be at least 70,300 megajoules. The embodied energy of the fiber is 2,812 megajoules. I have no estimates for the embodied energy of silica sand.
End of Life The recycling of post-consumer PVC is rare because the process is difficult and expensive. The Vinyl Institute has initiated a campaign to increase recycling, but PVC remains one of the least recyclable plastics.

The biggest hazard with post-consumer PVC is the chance that it will be burned, releasing dioxin and other toxins. The EPA claims PVC incineration?from household barrel-burning, commercial waste incineration, and landfill fires?is the largest known source of dioxin emissions in the United States.
As fiber-cement siding is a relatively new product that is long lasting, there are currently no programs to deal with it after its useful life. It could conceivably be reground and recycled or used as road fill.

If fiber-cement siding is sent to landfill, it will contribute to landfill volume, but as it is inert it will pose no lasting environmental or health issues.

For more information:

Read "What's the best affordable sustainable siding option? Any thoughts on roofing materials and gutters?"our Ask A Pro Q&Awith Carl Seville.

Environmental Building Newsletter article: "Should We Phase Out PVC?"

Sustainability information from the James Hardie Company, makers of HardiePlank fiber-cement siding.

Thanks to Daniel Bell, Dennis McCullah, and Dave Yarnell for their assistance with this question.