Whole-building LCA is about to get really big in LEED and elsewhere. It's a great tool, as long as you understand its limitations.

Are you designing the world’s greenest building?

If so, have your model line up here with all the others that have laid claim to the title. That’s right: single-family homes to the left, everyone else to the right. Today we’re finally going to settle this!

As soon as the bell sounds, start entering all your building’s materials into this hand-held life-cycle assessment device. I hope you all remembered to bring your carefully tracked site-visit mileage and the spreadsheets showing carbon released from the soil during construction? Also your energy models and decommissioning plans? GO!

And the winner is…

OK, OK, this would never work: buildings are complex, and there are just too many variables and unknowns. Also, you could never fit all the “world’s greenest” building designs into one room.

Yet to hear some people talk about the hottest new sustainable design trend—life-cycle assessment, or LCA—you would think it was the one and only methodology we need to determine whether a building product or a whole building is sustainable.

That’s ridiculous, and we explore why—along with what LCA does really well—in this month’s EBN feature article, “Whole-Building Life-Cycle Assessment: Taking the Measure of a Green Building.”

Below are five things to keep in mind when using LCA in your practice.

1. There’s more to life than carbon

Carbon is obviously one of the most pressing concerns of our time, and that’s driving many project teams to think really creatively about how they design. Building with wood radically reduces the initial carbon impact of a building, and we’re seeing a trend toward heavy-timber commercial construction based on results from whole-building LCA.

LCA isn’t so good at telling us, though, about the human-health effects of our materials (along with lots of other important metrics). Most heavy-timber glulams contain phenol-formaldehyde-based binders—which could give some design teams pause, given the amount of timber used and the fact that beams are typically exposed on the interior.

Another problem: although wood has had a long and respectable life as a structural material, we don’t know much yet about the durability of glulam timbers in airtight, high-performance buildings.

None of this is necessarily a deal-breaker, but it’s important to keep in mind that all decisions come with tradeoffs, even if you use LCA.

2. The Rumsfeld uncertainty principle

Former Secretary of Defense Donald Rumsfeld got a lot of ribbing for his statement about known knowns, known unknowns, and unknown unknowns. But the guy had a point.

The data behind LCAs is full of unknowns. We know exactly what some of those unknowns are: a lot of products and materials are just plain missing from our databases. But there are also holes in the data we have, and it may not be obvious what they are. Don’t lean too hard on those numbers; they might fall apart.

3. An ass of you and me

The foremost software tool in the U.S. for conducting a whole-building life-cycle assessment, or LCA, is called the Athena Impact Estimator. Not the impact X-Acto knife.

LCA isn’t like indoor VOC emissions, says lead LCA expert Wayne Trusty, past president of the Athena Sustainable Materials Institute. “You can’t take it in a lab and test it. It’s always about assumptions, projections, and estimates. That isn’t a reason to abandon it.”

Of course not—but it is a reason to define what your own assumptions are from the outset and to understand the assumptions behind any product LCAs you consult.

It’s also a reason not to let your marketing department send out press releases announcing your building is carbon-neutral or zero-impact. LCA simply doesn’t have the precision to determine that.

4. Twinkie earns nutrition label!

Here at BuildingGreen, we’re starting to see a lot more press releases about products “earning” environmental product declarations, or EPDs, the short-form report based on a product LCA. That’s like saying a Twinkie “earned” a nutrition label.

You don’t earn an EPD: you pay for it. (You pay a lot for it.) It doesn’t say a product has low environmental impacts but rather lays out what those impacts are. Don’t take the existence of an EPD to mean that a product is green.

Similarly, don’t take the use of whole-building LCA to mean that a building is green. LCA is a great tool for finding high-impact “hot spots” in the building overall during early design and then exploring systems or assemblies that might reduce the anticipated impacts as details are filled in. It’s not a seal of approval.

5. Blinding us with science

Have you heard about the scientist who used the same dataset to demonstrate opposite conclusions: that walking is better for you than running and that running is better for you than walking?

Advocates of LCA claim it’s more “scientific” than other methods of defining what’s green. For example, recycled content is often a good thing, but recycling is energy- and water-intensive and often involves a lot of trucking. It shouldn’t get a free pass. LCA is supposed to level the playing field so that we can fairly compare different products and materials.

Yes, LCA is science. But science is not the same as certainty: anyone who grew up thinking margarine was health food because it didn't have butter fat in it can attest to that.

As with a medical science, there are a lot of moving parts here: LCA is much more like an energy model than it is like a chemistry experiment. Like energy modeling, LCA is an excellent tool to help you estimate the impacts of your building. But don’t fall into the trap of thinking you’ve built a no-impact building just because your software zeroed out on the bottom line.

There is a danger that the patina of science will allow LCA to be used as a bigger, better style of greenwashing (we may even need to update our popular blog post “Nine Types of Greenwashing” to include “Blinding you with science”).

Use it responsibly

This kind of stuff is par for the course coming from product manufacturers, but we hope design firms won’t fall into the same habit. LCA is a powerful design tool but a terrible marketing device.

Read the article to learn more about how cutting-edge project teams are using LCA—and why even the world's foremost LCA experts advise caution.