Monday, June 23, 2008

Life Cycle Assessment is a Tool, Not a Silver Bullet

Are steel studs greener than wood? Is plastic pipe greener than copper? And is vinyl siding green?

By Peter Yost

There are few green building topics that produce more frustration and uncertainty than claims about the environmental footprint of particular building materials. Life Cycle Assessments, such as the ones listed below, seem like the perfect tool for summing it all up, but Life Cycle Assessments fall short for many reasons.

Getting reliable data is difficult at best
A life cycle assessment starts with a life cycle inventory. This means identifying and quantifying the inputs and outputs of a product from “cradle to grave” (mining, manufacturing, moving, installing, service life, and disposing of). This is no small task. And because much of the information comes from product manufacturers, the data can be incomplete -- manufacturers may not have all of the information or they may be unwilling to share it. When all products in a Life Cycle Assessment database are not scrutinized equally, conclusions drawn from the information may be misleading.

You can’t predict how many people will actually get cancer, only that a product could cause it
After the life cycle inventory is put together, it must be translated it into actual environmental impacts: global warming, human toxicity, ozone depletion, rainforest degradation, etc. This is called life cycle impact assessment (LCIA), and it gets pretty hypothetical. Many of these environmental effects require assumptions, such as how many lives will be lost from a particular cancer-causing output. These assumptions are impossible for normal people to evaluate, so we have to rely on someone else’s professional judgment.

They make apples to oranges environmental comparisons
The environmental impacts associated with a product are wide-ranging and measured in many different ways. For example, biodiversity may be gauged by the number of species going extinct and global warming by world-wide temperature rise. But how do we compare the two in relative importance? Again, it’s hard for normal people to evaluate the relative importance, so we must rely on trustworthy experts to weight each impact category in essentially an “apples to oranges” process. Is ozone depletion twice as important as the acidification of lakes? Pick your poison.

Setting boundary conditions is subjective and fuzzy
In any analysis, deciding what is on the table and what is out of bounds or beyond the scope is an essential first step. What does this mean in environmental life cycle assessment of building products? Three vexing examples provide valuable insight:

  • Open cell spray foam appears very green -- it insulates and air seals, it has no VOC off-gassing, uses water as the blowing agent, and it has proven to quite durable. But when considered in the greater context of a building, its excellent adhesion makes recycling or reusing the wood to which it is stuck difficult or even impossible. Should the insulation/air sealing properties be evaluated alone or should the effect on other building materials be considered?
  • Burning PVC is very bad -- when burned in uncontrolled conditions, PVC creates a serious environmental hazard. But if PVC waste from construction is rarely involved in uncontrolled burning, should this issue be included in the environmental profile of PVC plumbing pipe? Should burning be included in other PVC products, but not those used in construction?
  • Environmental regulations in other countries are often more lax that ours: A global manufacturer of paints has a good record of environmental compliance in the US, but a lousy record in countries with lax environmental standards. Do we consider the environmental degradation in other countries if we know the paint we are using is produced in the US?

Life Cycle Assessment is not a waste of time
Does this mean that Life Cycle Assessments and trying to compare the environmental profiles of competing products is a complete waste of time? Does it really matter which products we use from an environmental standpoint? The answer is that the environmental footprint of a product matters, but It should be put in the proper context:

  • Product selection should be among the last of the green building priorities. The energy efficiency, water efficiency, durability, and safety to human health of the building should be the top priorities.
  • Use building products manufactured and/or assembled locally and optimize the use of all construction materials (use fewer studs, design in 2 ft. modules, etc.).
    For the more complex LCA issues, go with product recommendations from a 3rd party, transparent, expert-based system such as TK.

Dive deeper:
Life Cycle Assessment for Buildings: Seeking the Holy Grail
Environmental Building News, March 2002.
Life Cycle 101
US EPA Life Cycle Assessment Research

Life Cycle Assessment tools:

--Peter Yost is Residential Program Manager at

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