If you've been in the green building world for a while, you've probably wondered about the embodied environmental impact of all the materials and such that goes into our built environment. And, in my research about the topic, I've found some things that might be more helpful than the in-depth analyses that we're relegated to for our projects. Given the cost of doing said analyses, we usually don't do them.
The first challenge that we confront is about metrics. Mostly we hear about 'embodied energy', and I'll stake out a polemical position here: Embodied Energy is a stupid metric. I challenge any of you reading this to tell me how embodied energy is either relevant or even quantifiable as an environmental impact indicator.
I suspect many of you might say "but do you know how many barrels of oil went into that spray foam" or "how many tons of coal go into concrete?"
And with those suggestions, it's not the energy content of energy source you're worried about, it's the environmental impacts with the extraction and combustion of said fuels. At least you've cited materials that have quantifiable energy inputs-- since that's in the form of fossil fuels which we're very good at quantifying since the stuff isn't free.
So-- let's talk about some different metrics.
- How about "embodied fossil fuel energy," or...
- Embodied Emissions of Particulates of less than 2.5 microns, or...
- How about one that's easy to get behind and global: Embodied Greenhouse Gas emissions
For the rest of this, I will be talking about Greenhouse gas emissions, because that's one that's well understood, and hopefully going to be well regulated someday soon.
Embodied carbon footprints in context
Rules of Thumb:
Alright, with metrics out of the way, let's talk about some rules of thumb about how to think about embodied GHG emissions without spending a lot of money sifting through numbers that we'll quickly be overwhelmed by.
First rule of thumb:
All other things being equal, more money=more environmental impact.
This should seem sort of obvious-- people don't screw up the environment for free. We're paying them to do it so we can get our cars fueled up and our cell phones charged.
Of course, there are a whole host of caveats and distorting factors to this-- government subsidies, differing environmental impacts of different industries and services. But the basic notion still holds true.
This is why the per-capita environmental impact of people in the first-world is so much more than that of third-world countries. People who spend only a little money (e.g. the world's poor) have a small fraction of environmental impact relative to us here on the top.
Ok-- so being cheap is a virtue, but we know that's not sufficient.
This notion is formally captured in the following database, hosted by Carnegie Mellon-- called Environmental Input-Output Life Cycle Assessment: Think of it as a sort of GDP country-wide assessment of environment impact.
Here's a website where you can look through it for free-- at Carnegie Mellon University.
This at least gives you the power to see what the environmental impact associated with generally with spending in certain parts of the economy. For example-- what are the environmental emissions involved with spending $100 in the "food/beverage/tobacco" industry? You probably never asked that question, but you can get answers there!
Of course, the main challenge with a tool like this is that it isn't product or sector specific enough to empower you to choose among different products/services within a defined sector. And it will never be specific enough to get down to individual brands.
Second Rule of Thumb: Less weight is better in construction
I did a non-academic study several years looking at a selection of 10 single-family residential projects that my firm had designed over the previous years, and specifically comparing it to our LEED-Platinum project.
In our research, we evaluated houses that ranged from 900 sq ft. to 9000 sq. ft.:
And we found something interesting (and don't you dare take this out of context):
SIZE DOESN'T MATTER.
Our smallest house didn't have the lowest embodied footprint, and neither did our largest house have the biggest footprint. The highest embodied footprint went to our LEED-Platinum house, and the 3rd largest footprint went to a house with about half the square footage.
Total Carbon Footprint
Well-- to rephrase the "size doesn't matter" phrase, let us now say SIZE ISN'T MATTER. If we step back, it's kind of patently ridiculous that we think that taking the area of the floor plane of conditioned space has anything but a very crude bearing on the embodied impact. Such impact is simply not defined by space-- since we all know that space is defined as the absence of stuff. Rather, it's the stuff that we use to define that space/volume that has the environmental impact. It's the sheetrock, the wood framing, the stucco, the metal lathe, the insulation, etc. And all that stuff is MATTER.
Since it's the stuff that matters, that's how we found the stuff that has less matter has less environmental impact. All of the houses with the highest footprints had a ton of concrete. And by 'ton' of concrete, I mean actually 10's and '100's of metric tons of the stuff. They were built like fortresses, and they'll probably last for eons if even a modicum of maintenance is performed on them.
The houses with the lowest embodied footprint (I'm thinking of Greenhouse Gas emissions especially-- just to remind you) were all light-framed construction. They were all wood covered with wood cladding and a light layer of sheetrock. The space/volume/floor area that they defined varied widely.
Durability: is it worth the gamble?
Many of our projects were built like fortresses in part for durability's sake. Heavier things tend to be more durable. Brick as a siding material is much much more durable than cedar shakes.
But is it worth it to incur the environmental cost of brick (kilned with natural gas) than to go with a less durable siding.
The devil is in the details. We found with our crude calculations (performed through the Athena Impact Estimator software) that the embodied GHG impact of clay roof tiles was worth 4-5 changes of cedar shakes. In other words, if the clay tiles would pay back after about 80 years relative to the cedar shakes. Is that worth it? maybe...
I say-- good look designing a building that lasts 80 years. It's not a question of durability of materials, but a durability of purpose-- or a building that 'learns'. Of course, that's a whole other subject that I'm not at all equipped to handle.
Carbon Footprint of Assemblies
Summing up: here's a crude recipe for a low impact house:
- Build it light
- Build it cheap
(Operational Energy) Build it well insulated (insulation is mostly air and therefore isn't heavy, and most insulation isn't expensive). A well insulated house shouldn't need additional heating.
(Operational Energy) For every energy service your house provides (e.g. refrigeration, cooking, entertainment, lighting): make it efficient and mostly turned off.
Contradictions, inconsistencies, fallacies?
If you've been following on and thinking carefully here, you'll find a number of tensions, and apparent contradictions and all sorts of other problems. I can say that at least for some of these questions, I've purposefully left them in here, since I'm approaching some complex systems with some crude findings. I see these apparent problems as ways for us to further explore the topic.
Feel free to comment below and I'll follow up as best I can.
Also-- feel free to email me at firstname.lastname@example.org if you don't want your question/comment published.
I look forward to your feedback.
About Luke Morton
I was born and raised in San Diego, but subsequently went off to Central California for college and around the country like some Bildungs-cience-roman. This included times at Stanford, Southface Energy Institute, Rocky Mountain Institute, and the US Green Building Council.
I've recently moved back to San Diego where I've been suitably impressed by the green building movement here. And in the meanwhile, I've inadvertently become a founding member of the San Diego Passive House Society where I am mostly good at standing in others' shadows.
Professionally, I work part-time for an architecture firm and a general contracting firm in the Bay area, and then informally manage to get involved in any project that seems to be doing something interesting. For better or worse, I fancy myself an educator first and foremost. Feel free to contact me anytime with any questions regarding energy efficiency, energy technologies, and building science, and you'll be able to test how much free consulting you can get out of me on the phone.
Image courtesy www.stockmonkeys.com