More Musings of an Energy Nerd
What’s embodied energy, and is there any reason to pay attention to it? Embodied energy is the energy it takes to manufacture building materials. Until recently, it was safe to advise builders that it wasn’t worth worrying about embodied energy, because the amount of energy (especially heating energy and cooling energy) used to operate a building over the building’s lifetime dwarfed the relatively small amount of energy embodied in the building materials.
As builders choose to install thicker and thicker layers of insulation in their buildings, however, the old rules of thumb aren’t working as well as they used to. Installing 6 inches of rigid foam insulation under a slab on grade may make sense in a cold climate; but if a Passivhaus builder decides to specify an additional 6 inches of foam, bringing the thickness of the sub-slab insulation up to 12 inches, it’s unlikely that the final 6 inches of foam will ever save as much energy as was required to manufacture the foam.
Defining embodied energy
The embodied energy of a building component or of an entire building is calculated by adding:
- The energy required to extract the raw materials used to make the building component (for example, the energy required to mine iron ore and make the steel wire that becomes a nail).
- The energy required to transport the raw materials to the factory where the building components are manufactured.
- The energy required to manufacture the building materials (for example, the energy required to transform steel wire into nails).
- The energy required to transport the building materials to the building site.
- The energy required to put the materials together at the building site, including the energy needed to transport the workers to the site.
Some, but not all, definitions of embodied energy include a few…
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35 Comments
Great overview
Great summary of embodied energy and the complexities and challenges of quantifying it, Martin. With net-zero-energy homes--a goal we should be striving for--reducing embodied energy is necessary if we are to further reduce greenhouse gas emissions.
Best Approach?
Great summary in terms of showing the complexities of this issue. It would be interesting to show the estimated embodied energy of PV panels as compared to the various insulations, particularly since there seems to be a lot of emphasis on this site for using a lot of PV over building to PH levels.
There is an argument to be made for multi-family housing as it is inherently more energy efficient and meeting Passivhaus levels of efficiency becomes easier with less insulation. I know this site is focused on single family housing, but this needs to be a part of the bigger discussion.
This is also an argument for really well designed housing (and buildings in general) that will be desirable for a very long time, effectively reducing the embodied energy. I know this site isn't about design, but it too needs to be part of the discussion. Poorly designed net zero suburban tract housing just isn't going to get us there.
Thanks for the Summaries
As an architect whose eyes glaze over whenever anyone starts talking MBTU's I appreciate the summary at the end and it jives nicely with common sense based on my limited knowledge. This ties nicely into the "Pretty good House" approach as opposed to the more rigid "certification" approach, whether Energy Star, Passive House, LEED or any of the others.
On the rules of thumb...
"Because foam insulation has a high embodied energy, it is hard to justify the installation of very thick layers of foam insulation."
This is true only for virgin-stock. For reclaimed/reuse refer to the first rule of thumb. There is multi-threaded environmental benefits to using reclaimed/recycled rigid foam. The energy and environmental hits of the reclaimed foam have already been taken, and shouldn't be re-assigned when re-used, extending the service life of the material. Transportation is primarily the new energy hit accrued, and that has to be balance against the transportation and other environmental hits of otherwise disposing of the material.
There is a case to be made that NOT re-using rigid foam is wasting the embodied energy (and environmental damage related to it's manufacture), and building assemblies with thick reclaimed foam is likely to embody less NEW energy than virgin-stock cellulose.
It's the same argument of discounting the prior manufacturing energy is what is used for cellulose. Most energy accounting analyses for cellulose insulation usually ignores the paper-making energy, using primarily the manufacturing & transportation energy related to the processing of the scrap paper and the fire retardents, etc. As the market for newsprint continues to shrink, and printing over-runs become reduced by "print on demand" publishing & better management, it would be curious to see a careful accounting of the embodied energy of cellulose as if it were being manufactured using virgin pulp rather than reclaimed/re-used goods. The raw manufacturing BTUs for kraft paper is about 9000 BTU/lb (and that's before transportation and other processing and not including the raw log felling & transportation) To hit R20 with dense-pack at 3.5lbs/ per cubic foot takes about 0.45 lbs, and for loose-fill it's a bit less than half that, so that's ~4050 BTU per square foot of dense-pack, maybe 1800 BTU per square foot for R20 loose fill, just in manufacturing energy for the paper. The only way it gets to 600 BTU per square foot for R20 is if you're only counting the processing, transport, and installation energy use, and very little or none of the logging & paper manufacturing energy. If the scrap paper market ever gets to the point where a fraction of virgin-stock needs to be introduced, it's not clear that cellulose would continue to be the low embodied-energy winner that it is today.
Response to Jeff Stern
Jeff,
Here is some information on the embodied energy of PV equipment, from an article in Home Power magazine: "The EPBT [energy payback time] for standard, single-crystalline module PV systems [is] two years." According to the author of the HP article, Justine Sanchez, the study included the embodied energy of balance of system (BOS) components (racks, inverters, wires, etc.) and assumed a system efficiency of 75%.
The output of a PV array depends on its location, of course, but a general rule-of-thumb is that a 1-kW PV system will produce 1,000 kWh per year in the Northeast U.S., or 1,600 kWh per year in the Southwest. So it's fair to assume that the embodied energy of a 1-kW PV system is about 3,000 kWh, or 10.2 MMBTU.
You may also be interested in comparing the energy savings associated with investing in PV compared to investing in foam insulation. Mike Eliason shared an example of a calculation (quoted in my article) showing that an investment of $325 for 2 inches of additional EPS would have saved 81 kWh per year. If an equivalent amount were invested in a PV system costing $4.50 per watt, it would produce 70 kWh per year in Seattle. So the EPS is a better investment, but just barely.
If the PV system costs $3 per watt, then a $325 investment in PV yields 105 kWh per year -- a better investment than the EPS foam.
A $325 investment in PV system will give you a system rated at between 76 and 108 watts. (For the time being, we are going to ignore the fact that it's hard to buy a PV system that small, because we are simply trying to demonstrate a principle here.) If the embodied energy of a 1-kW PV system is 3,000 kWh (10,800 MJ), then the embodied energy of a PV system costing $325 ranges from 820 MJ to 1,166 MJ, or between 30% and 43% of the embodied energy of $325 of EPS foam. So the PV system has less embodied energy than the rigid foam.
Response to Robert Swinburne
Robert,
You wrote, "I appreciate the summary at the end and it jives nicely with common sense based on my limited knowledge. This ties nicely into the 'Pretty good House' approach."
I agree. As we all get bogged down in this type of math, it's easy to oversharpen our pencils. It's important to remember that these calculations are based on very rough numbers, and in some cases on guesses. That's why the rule-of-thumb approach is sensible here.
Response to Dana Dorsett
Dana,
Thanks for two excellent points. Concerning your point about recycled rigid foam, it's a point worth making. I think I'll edit the article to reflect your observation.
I also appreciate your back-of-the-envelope calculations concerning the embodied energy of cellulose insulation. The collapse of the newspaper industry is alarming not only to journalists and publishers; it is also alarming to cellulose insulation manufacturers, who see the writing on the wall, and don't like what they see.
Circle of Junk
I think it was Paul Eldrenkamp who came up with "attic recycling" - insulating a client's attic by shredding its contents. Brilliant.
Response to Dan Kolbert
Dan,
So that's what we need to do with 25 years of National Geographics, and those bags of clothes that don't fit anymore.
What about mineral wool under slab?
I was surprised to see that mineral wool is, while much higher than cellulose, still much lower than foam or even fiberglass. I guess melting rock doesn't take as much energy as I had expected. Or is the mineral wool benefiting from being made from a recycled feedstock, similar to cellulose?
At any rate, one of the issues that seems to come up over and over again in Passivehouse discussions is the appropriate level of underslab insulation. This seems to be a more contentious issue than wall or attic insulation, perhaps because in most places underslab insulation isn't used at all.
All of these discussions seem to proceed from the assumption that foam is the only reasonable option for under slab insulation. Obviously fiberglass won't work, much less cellulose (shudder!) but what about mineral wool? My impression is that this material can be made as rigid and stiff as any foam, and it's naturally rot-proof. And per a recent GBA post, it's typically cheaper than foam. So is there a reason why we're not using it for underslab insulation?
Also: Dana, thank you very much for your points about cellulose. I was not aware of that issue, and it's really good to be able to see past the numbers to the underlying dynamics of the situation.
Response to Brent Eubanks
Brent,
I've heard of a few builders experimenting with the use of mineral wool insulation under slabs, but as far as I know, the application is not yet approved by any mineral wool manufacturer distributing in North America.
I think that the best approach to subslab insulation is to use common sense -- and to stop at 4 inches or 6 inches of foam, as almost all experts recommend. Were it not for PHPP software and Dr. Feist's famous 15 kWh/m2*year target, no one would be installing 10 inches, 12 inches, or 16 inches of sub-slab foam.
Certifications Etc.
I couldn't agree more with Robert and Martin on the inherent lack of logic in chasing these certifications. The cult-like passivhausers are particularly amusing with their window assemblies and under-slab insulation. In my mind, the "pretty good house" approach is the best overall, especially when you add regional logic to the equation.
Unfortunately, consumers drive what we are building and consumers need certifications. If you build a pretty good house right next to some guy who builds an energy star house, with price and other things being equal, chance are the Energy Star house sells before yours. Without the use of tools like the Energy Performance Score here in Oregon, which is basically an index of how much energy the house will consume, even energy conscious consumers will go for the poorly built Energy Star house. Even with tools like the EPS, the rating system is only as valuable as the public's familiarity with it. If people aren't aware of the EPS, they won't make purchasing decisions based on it.
I guess what I'm saying is that it seems as though the certifications are a necessary evil of sorts. I wish we could just build good houses and the consumers would come running, but that doesn't appear to be the case. People seem to like seeing that Energy Star label, no matter how green washed it has become. I wish we could somehow combine the LEED and Passivhause certs in to a regionally specific tool that everyone recognized, but that hasn't happened yet. My personal opinion is a well built net-zero home is about as good as we can currently build. But even then, if the public doesn't demand it we will only be building it on the smallest of scales.
If we really want to make a dent in how much energy our houses consume, I think it's going to have to be with the use of some kind of rating system and certification. Building custom houses that are energy efficient and well built is a good thing, but it ain't gonna change our climate problem.
Recycled foam under slabs
Dana, where I build I'm thinking used foam would work under slabs. Laid on open draining gravel with poly between it and concrete why not? I build dry basements either because they will be dry naturally or we install a pretty good drainage set up.
If high humidity is a problem, a semi use idea would be to use a normal underslab EPS or XPS as a separation layer.
So... going way up in inches of under slab thickness, one could get there for way less coin and also lower the embodied energy number to boot... win win...
As to embodied yak... not taking into account populations in relation to all pollutants all positives, lifestyle gains, losses, and the whole of nature, the universe... well... I think embodied energy is just one very minor player in the all of all.
Everything depends on harmonic joining of all the parts of the universe which humans and there making of homes with some embodied energy number... well.... I see no picture being drawn with this blog. Maybe my post will get one of you to post some clarity.
How Far Do You Take It?
I ran into someone who telling me about the "embodied energy" of population growth. How people should limit the amount of children they are having since a child born into the world and all the pollution they will contribute throughout a lifetime is a monumental amount. They even had stats and data to prove their point about how much a person from birth to old age will contribute to the carbon footprint of the world.
The green energy world, like any group, has its moderates and ultra conservatives. For some, building to code is adequate while others believe that one shouldn't even build a new home but live in earth caves and live off of the grid. There is a "I'm greener than you" type of vibe out there. It almost takes on a religious type of role. All of us have experienced it within our "green travels" while talking to people who are interested in our planets health and building green.
So the question comes back to is how far do you take it? The ROI and diminishing returns question is what the above article addressed. I agree that there comes a point when one can "over insulate" a building and the payback becomes 50-100 years later. Even with cellulose, what about the embodied energy behind the planting of the seedling, watering and fertilizing it for years before it can be cut and harvested. What about the diesel trucks that have to carry and transport the logs to lumber mills. What about the lumber mills and the pollution they contribute running their machinery. Then the lumber is converted to paper and ink is placed on the paper. The polluting trucks carry the paper to delivery locations. I can go on and on and make cellulose and it's embodied energy hit the 20,000+ BTU mark. It's all on what data you gather and how you analyze it. Going from seedling to cellulose being stuffed into a wall cavity has a lot more embodied energy than the article touched on.
The point of all of this is that building green is our goal but it spans the entire gamut. From those who think building green is using recycled tires & glass and building an earth ship to those who think sticking R-100 in the attic and R-50 in the walls of a 4,000 sqft home is building green. One size doesn't fit all and hopefully we don't over-analyze this whole "embodied energy" thing. Yes, it is a valid principle but one can argue about how much embodied energy is used to power our computers to talk and blog about embodied energy ;)
Response to Peter L
Peter L,
I agree with you that very precise calculations of embodied energy are a waste of time, but perhaps for different reasons. My main reason: precision is impossible.
You raise the same question raised by Dana Dorsett: should we include all of the energy inputs used to make newsprint when calculating the embodied energy of cellulose insulation? I would argue: no.
When I was growing up, people threw their newspapers in the trash, and disposing of old newspapers required energy inputs and landfill space. I was part of my high school's Ecology Action club in 1970 through 1972, and back then, the idea of recycling newspapers was brand new. We tracked down a place in Waltham, Mass., that accepted newspapers for recycling, and once a month we had a paper drive at the high school. Parents would come and drop off their newspapers, and my father and I would drive the newspapers to Waltham in the family pickup. It was improvised, informal, and unusual back then.
So if recycled newspapers are turned into insulation, it solves the landfill and disposal problem. So we shouldn't count the energy required to make the paper.
You raise another question: "What about the embodied energy behind the planting of the seedling, watering and fertilizing it for years before it can be cut and harvested?" I live in northern Vermont. In this part of the state, and adjacent northern New Hampshire, loggers have been cutting pulp and hauling 4-foot pulp logs to pulp mills for decades. The pulp mills just began closing during the last 5 years.
I assure you, no one plants seedlings for pulp. No one waters the seedlings. No one fertilizes the trees. Loggers only turn trees into pulp if they can't be sold as saw logs. It's just ordinary spruce and fir that grows up in the woods like weeds.
embodied energy of retrofit projects
We're still barely into the research, but our initial calculations suggest that over 60% of the embodied energy of our home renovations comes from getting workers from their homes to the jobsite and back. This is much higher than I would have guessed. All those 20%-efficient internal combustion engines traveling at 15-20 miles an hour in metropolitan Boston traffic are responsible for some serious Btu consumption.
I assume it's different for new construction, where the materials-to-labor ratio is higher. But it seems clear that if we want a good return on energy investment for a remodeling project, we can't just do the bathroom or kitchen renovation. We need to make sure that when we're on the job doing those sort of projects, we're also doing as much air-sealing and insulation work as the budget allows.
Simple answer
Just move in for the duration of the project.
A useful metric?
Nice overview of a complex and otherwise confusing topic.
In my past conversations with people/clients who've talked about embodied energy in the context of other metrics included in a Life Cycle Inventory, we've been confounded as to why embodied energy is a useful metric in green buildings.
1st-- Renewables?
If we take as a given that embodied energy is the input of fossil fuels from the "Source to jobsite" of a material's life, then it seems a decent proxy.
But what about the following (albeit contrived example):
Two cement calcining plants-- one uses coal for process heat, and the other uses solar (PV or other). The embodied energy of the output portland cement would be roughly the same, but here the metric seems to leave out something we care about.
2nd-- Embodied Energy cost parity? and insurance?
I definitely concur with all the discussion that installing 24 inches of subslab insulation to meet a magic number seems a little silly given the alternatives. BUT, I don't think the simple math of 'install insulation only up to the point where there is a positive lifetime energy payback' is a sufficient boundary for an optimization. Would that math work for off-grid houses where the costs for storing and providing a BTU would be much higher than for grid-connected houses?
And what about investments into Autarky? Might we see an investment in up-front embodied energy costs as a way to provide a form of energy 'insurance' for extreme events in our buildings that aren't captured in the dismal accounting of future energy budgets?
3rd-- Exergy:
I'll see if I can call Dr. Bailes here out on the floor to see if there are any insights he might have about embodied energy from a physics point of view. It seems to me that all BTUs aren't created the same. I'm not positive about this, but I suspect this is why ASHRAE doesn't use BTUs, and instead uses Energy Costs as its final metric of comparison in ASHRAE 90.1. And I KNOW its why California uses "Time-dependent-value" instead of BTU's for its Title 24 calculations.
embodied energy
Good article. We'll look into recycled EPS for under-slab work, but I'm thinking the time and energy required to use it may eat up much of that savings. I wonder also about the embodied energy of construction materials like TJIs and plywood as compared to rough boards or standard solid lumber? TJIs have a number of advantages, ease of use, ability to easily build wider spans as well as the decreasing quality of solid lumber, but at what price?
I have one minor criticism: the life cycle mentioned is 50 years, but Passive Houses and Pretty Good Houses should last far longer than the average building, so that should be part of the equation.
And Paul brings up trucks: I'm trying to hold off replacing my 11 yr old, 12 mpg, 3/4 ton F250 until I can buy one that gets 40 mpg, but looks like it will be a long wait. Just tripling truck mileage would go a long way toward decreasing carbon useage in the construction field.
Response to Lucas Morton
Lucas,
As if embodied energy calculations weren't already complicated enough, you are proposing that we add a new layer of complexity, by distinguishing between "good" BTUs and "bad" BTUs. But who is going to make the necessary judgment? Is an aluminum plant that uses hydroelectricity in Iceland better than an aluminum plant that uses electricity produced by natural gas in Missouri?
I'm not denying that the question is interesting... but the only possible conclusions are: (a) these calculations are complicated; and (b) it behooves all off us to reduce our consumption of energy.
Response to Bob Irving
Bob,
You wrote, "The life cycle mentioned is 50 years, but Passive Houses and Pretty Good Houses should last far longer than the average building."
First of all, I made no assumptions. I wrote, "You can’t calculate how much energy ... insulation will save unless you know when the building will be demolished."
I did quote from academic papers that included calculations based on 50-year lifespans.
Predicting when a building will be demolished is tricky. Certainly, the builders of the superinsulated homes of the mid-1980s were (like you) convinced that they were building for 100 years. But many of these homes have been extensively altered since then.
Hundreds of buildings are bulldozed every year in Detroit, Cleveland, and Philadelphia. Many of these buildings are solidly built brick buildings with firm foundations, high ceilings, and beautiful interior woodwork. But no one wants to live in them, so the buildings are being demolished.
When I had my own business providing capital needs assessments, I learned that most residential buildings are substantially rebuilt every 30 years. After 30 years, a house needs a new roof, new kitchen, new flooring, and new bathrooms. In many cases, the house needs to be reconfigured because lifestyles have changed. In some cases, the house may even need new siding and windows, although these components generally last longer than 30 years. It isn't unusual for these renovations to cost as much as the original construction.
So, how long does a house last? Your guess is as good as mine.
Embodied Energy of Mineral Wool
Should the embodied energy of mineral wool include some of the energy required for steel manufacture? Or should mineral wool get bonus points because it is made from a recycled material. It's the same discussion with cellulose. And like the reduction in newspaper publishing affecting the future of the raw stock for cellulose, very little steel is smelted from raw ore in the US any more, at least not compared to the last century. What happens when we run out of left over slag? What about mineral wool that is made primarily from virgin basalt?
Apparently I am full of questions, and don't have many answers this morning. This is such an interesting topic and discussion I want more information. So thank you to Martin, et.al. for bringing this up.
Response to Eric West
Eric,
As far as I know, almost all of the mineral wool insulation manufactured in North America is actually slag wool rather than rock wool made from basalt. Even though the volume of steel manufactured in North America may be dropping, I haven't heard of any slag shortages yet.
Response back to Martin
Thanks Martin--
Perhaps I am interested in distinguishing between 'good' BTUs and 'bad' BTUs. I definitely understand the argument that this defeats the purpose of the metric of embodied energy-- sure it's crude, but it's a lot simpler and easier to get than some overblown LCA. Of course simplicity obscures the complexities that lie underneath.
I'd have to agree that in many, if not most questions, reducing embodied energy is well correlated with reduction in the real environmental impacts that its a proxy for.
Your example of the aluminum smelted with hydro vs. natural gas is a great example. If we have to have aluminum for some reason, which one would better reflect the clients' environmental values?
This goes for the negative side too-- let's say we find the optimal embodied energy level for R-245fa based ccSPF insulation-- would that be the same level we would find if we optimized for global warming potential?
Well-- I'm just making a mountain out of a molehill, aren't I? Perhaps the answer is that embodied energy isn't a specific enough metric for a wonk like me :)
Embodied Energy
Thanks for the good words on embodied energy.
You may be interested in a superinsulated house report that I coauthored at Brookhaven Lab 30 years ago wherein we took our first stab at embodied energy analysis. This publication has been unavailable, but I finally dug up an unbound copy and scanned it and put it on issuu where you can see it for free. http://issuu.com/flash.swank/docs/case_study__blouin_superinsulated_house
We used embodied energy unit values that were derived from the work from Dr. Bruce Hannon at the University of Illinois, Center for Advanced Computation, which is presumably the old data to which you referred. We thought that this data was old 30 years ago. It turned out that Dr. Hannon didn't necessarily approve of this use of his data, which was based upon a detailed model of the US economy in 1967. The guys I talked with at the Energy Information Administration at the time thought that it might be better to use financial data as a proxy for embodoed energy unit values, as energy is some component of the cost of an industrial material, and the amount of assumptions in determining emboded energy unit values is so large.
We did extremely detailed estimating of the materials required to build the subject building to different efficiency levels, and applied the unit energy values and measured and modelled the resulting energy consumption. Our results showed the energy economics of the incremental efficiency upgrades applied to that model matched the financial economics fairly closely.
My limited current searching indicates that the data on embodied energy per unit of material hasn't improved much in 30 years. The reports cited in your blog seem to indicate that the data is all over the map.
Response to Daniel Hagan
Daniel,
I am extremely grateful for your comment, and for the link to the document from 1983. This is a fascinating paper which provides important details relevant to the history of superinsulated houses in the U.S.
I haven't finished it yet, but it is already riveting.
Time Scale, ICE
Thank you for this well-conceived and well-presented article. EE of building materials has been a big consideration for us from the beginning, and rather than seeing it as an 'either-or' position compared with operational energy, we can often make decisions that allow for a 'both-and' result.
Another really important reason for consideration of material EE, especially when comparing between two different materials (as opposed to thickness levels) is the fact that high-EE materials need to operate in a service life for a period of years to offset the cradle-side carbon-equivilent emissions. We don't have years and years to wait to have insulation materials 'break-even' before they begin positively affecting global warming potential; we need to have saved that carbon years and years ago. High-EE insulations are essentially front-loading emissions equal to the first 5, 10, 15 years of energy savings when compared to equivalent performance from a low-EE insulation, and that time scale really matters right now.
A resource you all might find helpful in quantifying embodied energy, embodied carbon, and embodied carbon-equivilent is the Inventory of Carbon & Energy, published by the University of Bath, UK. It is an incredible wealth of well-annotated, well-referenced, well-organized information documenting nearly every building material you are likely to encounter. It has been very valuable to our research and development. Those of us in the US need to take with a big pound of salt the geo-specificity of their research (UK), but those effects are annotated well throughout the document. Here's a link to a possibly outdated version hosted on an MIT server):
http://web.mit.edu/2.813/www/readings/ICE.pdf
Cheers,
Jacob Deva Racusin
New Frameworks Natural Design/Build
How about this:
Hmmm. How about this: The "embodied energy" calculation also needs to count labor and the consumption required to fund it. That is: If you tear down a serviceable (but less energy-efficient) house worth, say $200,000, and replace it with a more energy-efficient house that cost you $300,000 to build, you just created $300,000 in consumption that must now be "recovered" in energy savings to make sense. Golly, it will take you a lotta lotta time to make up that amount of savings in energy-cost, energy-spending. It's exactly the same as the replacement window issue. It just does not make economic sense to replace the old with the new, you will never get it $$$ back. What do you think, Martin? Am I mis-thinking something?
Response to Pam Kueber
Pam,
I'm not sure, but I think you are confusing cost-effectiveness calculations and embodied energy calculations. Both types of calculations are useful.
You seem to be describing a calculation that looks at the cost-effectiveness of demolishing an existing building and replacing it with a new, more energy-efficient building. Performing such a calculation is relatively straightforward; for more information on this type of calculation, see Payback Calculations for Energy-Efficiency Improvements.
There is one big caveat to this type of calculation, however: no one ever demolishes a building for the single reason of trying to save energy. People demolish buildings for multiple reasons, so it's a little unfair to require the better energy features (and associated energy savings) to carry the entire burden of the demolition and construction costs.
This article discusses embodied energy calculations, not cost-effectiveness calculations. Of course, it's possible to discuss the embodied energy implications of a job involving the demolition of an existing building and its replacement by a new, more energy-efficient building. I discussed that type of calculation in the article above, under the heading "New construction versus rehabbing existing buildings."
Response to Martin Holladay responding to me
Hmmm. All of this seems like a difference without a distinction to me. Whether you call it "energy" or "carbon" it all rolls up into MONEY -- which seems to be about the best proxy I can think of for "green". As in, it is only the cost-effective improvements that make sense -- that will truly slow environmental degradation. "Improvements" that are not cost-effective -- that do not have the payback -- are not "green", they are making climate-change matters worse -- they are just more consumption.
Response to Pam Kueber
Pam,
You wrote, "All of this seems like a difference without a distinction to me."
I will propose an example that may help you see the difference between a cost-effectiveness calculation and an embodied-energy calculation.
Imagine two houses. Both have insulation with the same R-value. Both houses cost about the same -- let's say $250,000.
One house is insulated with spray polyurethane foam; the other is insulated with cellulose.
The energy performance of the two houses is about the same.
If you consider the cost of the entire house, the cost-effectiveness of the two insulation solutions might be about the same. (For example, the walls of the spray-foam house might be thinner, so the framing was cheaper but the insulation was more expensive -- so the cost of the two systems was a wash.) The cost-effectiveness and payback calculations show the same result.
But the embodied energy calculations will be very different, because spray foam has more embodied energy than cellulose.
Homeowners take caution. Embodied energy is a slippery slope into insanity.
I have been working for years on the front lines of zero energy homes and constantly watch people quote embodied energy as their rationale for design choices when comparing unequal assemblies. Yes, unequal assemblies. This is insanity.
The first priority in envelope design must be construct-ability. A poorly constructed house is a waste of all of it's embodied energy, period. Design must be assume that the workers on site have training doing repetitive tasks, not unique assemblies developed by an over-eager architect trying to achieve the lowest possible "embodied energy."
If, as Paul E mentioned earlier, over 60% of embodied energy comes from the worker's coming and going from construction sites. Why are we designing projects of 2-5x the complexity resulting in increased chance of failure and construction duration?
"Why are we designing projects of 2-5x the complexity resulting in increased chance of failure and construction duration?"
Because we have to, if we want to continue living any semblance of our current lifestyle and certainly if we want our descendants to have a livable planet. Yes, that sounds like hyperbole, but it's what the world's best scientists are telling us. There is always an easier way to do something, but that doesn't mean it's a better way. Once workers are trained, none of the high-performance, low-carbon approaches I'm aware of are particularly difficult; they just take more attention to detail than the methods I learned in the 80s.
Moving toward off-site fabrication is one approach that can make a lot of sense, but it's not ideal for every situation.
A minor point--currently, it's not embodied energy that's important, but closely-related embodied carbon.
I keep reading Dana's comments on reclaimed foam. I live near Ottawa, Canada. I have looked for it a few times and never could find any reclaimed rigid foam close to home. Is this something more common south border or have I been looking in the wrong places?
On another note, there is something that keeps bothering me lately. I currently heat with natural gas. I presume that under certain conditions, adding a small amount of EPS/polyiso, let's say an inch, on the inside could make sense in a 50 to 60 year time frame.
However, if I switched to electric heat, which is almost 100% hydro in my area, wouldn't if become very difficult to justify any extra insulation?
In a scenario where heating and cooling is done with electricity with 98-100% hydropower, does it make sense environmentally speaking to use a heat pump rather than an electric heat given the higher GHWP of refrigerant?
How does the embodied energy part of EPS change if it is produced in a factory that uses 100% renewable energy? Is there more embodied energy in the actual rigid foam or is the process the main culprit?
The calculation is more complex than this as Hydro-Quebec needs to buy power from the US/Ontario during peak utilization in the winter. At any rate, my initial conclusion is that it is incredibly complex for an individual to make the correct choices to reduce greenhouse gas emission, at least in the building industry.
How to make it easier?
Sofiane,
You asked a lot of questions, and I'll address a few of them. Other GBA readers may choose to respond as well.
You're right that the availability of used rigid foam varies from region to region. I have no idea how hard it is to buy rigid foam in Ottawa, but it may well be difficult.
Concerning the logic of investing in extra insulation to reduce fuel use: some people analyze this type of decision by looking at economic savings, while others analyze the decision in terms of global warming potential. Needless to say, these two types of analyses are different. Sometimes, an investment that makes no economic sense may still help the planet. On the other hand, sometimes an investment that saves money in the long run ends up hastening climate change. For more information on economic analyses, see "Payback Calculations for Energy Efficiency Improvements."
If your local utility delivers electricity that is generated by hydroelectricity, the CO2 emissions associated with producing this electricity are very low, so investments to reduce electricity use will have very little environmental benefit, especially compared to similar investments in a community where the local utility generates electricity by burning coal.
I agree with your statement, "My initial conclusion is that it is incredibly complex for an individual to make the correct choices to reduce greenhouse gas emission, at least in the building industry." In my article, I wrote, "Unfortunately, there are so many uncertainties in embodied energy calculations that designers can be forgiven for just throwing up their hands and giving up." We can't nail down precise numbers when we make these calculations -- all we can do is aim in the right direction.
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