Thursday, August 5, 2010

Carbon Offset Value of Straw Bale Houses

One of my goals in moving to Ithaca was to get into a position where I can began transitioning my family to a carbon-negative lifestyle.  Obviously writing posts about alarming climate papers only goes so far; if one isn't prepared to personally do something, at some point it starts to feel hypocritical (at least it does to me).  This process is absolutely in its infancy, but I plan to blog about it to a certain degree.  Our experiences may be helpful to others traveling along the same path.  Perhaps a few other people who wouldn't otherwise have contemplated this will get the idea.  And at a minimum, I will be able to feel less guilty, and more smug and self-righteous, as the climate goes to hell around us.

To begin with, I need to get up to speed on the basic arithmetic of what it would mean for my household to be carbon neutral or negative.  I want to do the math with enough thoroughness that I can be confident that goal is really achieved.  And I also want to do the math on the scalability of the particular choices we end up making, so we understand those tradeoffs too.  While there's some value to doing niche things that wouldn't scale, there's obviously a lot more value in doing things that do have significant scaling potential.

Since housing is the largest asset most families have, it's obviously the place to start, and strawbale construction seems like one of the most potentially attractive options in terms of carbon capture, as well as ongoing energy efficiency of the building.  In googling around, I've found it surprisingly difficult to find good numbers on this, so I'm going to start with some back of the envelope calculations to give a feeling for the scale.  (Feel free to provide references to better calculations in comments).

Many readers may wish to gloss over the math in the next few paragraphs - there will be no test!

In this document we find some basic specs for the size and weight of a straw bale as follows:
Straw Bale Size: Each straw bale shall be a minimum of 360 mm (14 in)
wide, 450 mm (18 in) in height, 900 mm (36 in) in length and shall have a
minimum mass of 23 kg (51 lb.)
Let's figure the straw equilibriates at 15% moisture content by weight (it can't go over 18% or it will rot), so the dry weight of a bale is 45lb in round numbers - about 20kg.  Next let's assume as a first approximation that the dry straw is basically cellulose with a chemical formula of C6H10O5. Now the atomic weight of carbon is 12, that of hydrogen is 1, and oxygen is 16.  So, remembering our high school chemistry, the fraction of the weight in carbon in the above formula is 6x12/(6x12 + 10x1 + 5x16), or 45%.  So our 23kg bale would hold 8.9kg of carbon if it was all cellulose.  Let's call it 8.5kg to allow for a few percent of ash content in the straw.

Ok, so let's translate this into house terms.  The median house size in the northeastern US got up to 2600 sq feet in 2009.  Let's figure on a two story structure, with 1300 square feet per floor, and to keep it simple, let's suppose that comes from a rectangle 45' x 29' on its inside dimensions.  Let's also figure the bales are stacked on the flat side for maximum carbon capture and insulation value.  So the bale is 14" high, and thus if we stack them 15 high, we'll get 17.5', which seems enough to allow for two stories, plus some floor thickness and compression.  We have two long walls at 48' (16 bales long), and two short walls at 29' (9.67 bales).  So the total baleage (is that a word?) is 2x15x(16+9.67) = 770 bales.

That comes to 6.5 metric tonnes of carbon.

Note this ignores that a real house plan would probably not be a rectangle, thus using more bales, neglects carbon capture in the rest of the building (especially wood framing and interior walls), embodied carbon emissions in other components (especially a concrete foundation), transportation emissions associated with getting components to the building site, etc, etc.  But let's just play with the 6.5 tonnes number for a minute, now that we've gone to the trouble of getting it.  How much is 6.5 tonnes?

Well, let's compare it to average carbon emissions.  For the United States, carbon dioxide emissions per capita are about 19 metric tonnes/year, which corresponds to 5.1 tonnes of carbon.  Per person.  So for a family of four, living in that median sized house, average share of carbon emissions would be about 20.4 tonnes/year.

Thus the carbon in the house's straw-bales offset about 3 1/2 months of emissions.

Not so good.  Clearly, to be carbon negative, our hypothetical family is going to have to emit a lot less than the US average.

Of course, it's probably not fair to consider a house as offsetting carbon emissions across the whole economy, versus the family's own activities.  With some care in design, the straw bale house is going to consume little energy to heat and cool, so another way of thinking about the scale is relative to driving behavior.  Let's suppose the family were to drive about 20,000 miles per year, at 20mpg, thus requiring 1000 gallons of gasoline.  That contains 2.450 tonnes of carbon.

So the straw bales would offset about 2 1/2 years of that kind of driving.  More or less, depending on how much driving and the fuel economy of the vehicles in question.

That's not that impressive either, given that the life of the building is going to be measured in decades.

One last calculation.  How much air travel does this straw bale offset?  Well, air travel involves about 0.2kg per passenger mile.  So the 6.5 tonnes of straw bales will offset about 32,500 miles of air travel.  A round the world trip!  One round the world trip.

So, I think the main conclusion is this: the carbon capture in a straw bale building is nowhere near enough to offset the carbon emissions of normal US fossil fuel usage for anywhere near the life of the building.  One would have to get fossil fuel usage down to a very small fraction of the typical total, and then the carbon offset in the building might be useful.


Burk said...

Hi, Stuart-

Great blog. But I would differ on the hypocrisy of promoting climate change policy while doing little on one's own to mitigate it. Certainly, it is virtuous to do both, but changing policy is far, far more important- on a whole other order, in fact.

We live in an economic system. Any fossil fuel that I save will decrease its cost and render it that much cheaper for someone else to waste. Thus conservation becomes a zero sum game without a larger policy that makes it more expensive for everyone.

While it is possible that Americans can be persuaded to escape this economic rationale and save money in absolute terms while saving energy and going green, etc., we have reason to be profoundly doubtful. Inertia and greed are retarding us in both the economic and political arenas, so it is hard to have hope either way. But they are deeply different projects.

Mike Aucott said...

In my view the basics of a low-carbon lifestyle at the residential level are living in a small, very well-insulated house, sited and dimensioned so as to be shaded in the summer and warmed in the winter by the sun, using energy-efficient appliances, not eating a lot of meat, and doing a minimal amount of driving. Consistent with your analysis, the amount of carbon you could sequester in the construction itself, whether it be in the form of straw bales, wood, whatever, is virtually certain to be trivial compared to the yearly flow of carbon related to heating, cooling, eating, and moving around.

Anonymous said...

I agree with your feelings and that it takes a lot of time to adjust from just talking (I have been doing that for years) to changing behavior. I am fairly low energy for a Western person and getting into a low energy house is my next step. I just can't see getting off the grid or buying only local food or being even partially self sufficient in food production living in an urban seeting although some of these things seem sensible and I would love to somehow give it a crack over time as opportunities present themselves. All those cheap imports of all sorts would be tabu too. My kids ought to learn these things from us so they won't have such a big shock when it is more or less necessary.

Stuart Staniford said...


Well, I certainly don't want to get into telling anyone else what they should or shouldn't do. However, my general feeling is that my ability to affect policy is pretty damn limited, and in so far as I have any, it's likely to be considerably enhanced by putting my money where my mouth is, and creating one more worked example.

I completely agree about the displacement issues at a macroeconomic level. But at an ethical level, I tend to feel that I'm only responsible for my own choices. If other folks choose to use any fossil fuels I may end up hopefully conserving, that's their responsibility, not mine.

Stuart Staniford said...


I suspect the design envelope for how to be carbon neutral/negative is larger than you think, and different folks will make a different set of tradeoffs.

Stuart Staniford said...


I'm not at all persuaded that eating locally is necessarily more energy or climate efficient. J.D. at Peak Oil Debunked had some links and back-of-the-envelope calculations that I think are more-or-less in the ballpark.

I I'm afraid that eating locally is a feel-good-fuzzy-about-the-math distraction from the real issues...

I also think getting off the grid is probably fairly unhelpful to the cause of having a decent life while being carbon neutral. Being off-grid forces you to meet your own energy demand at all times, instead of being able to amortize across the year (eg producing a surplus of solar power in the summer, and then running a deficit in the winter in order to heat the house and drive in the snow).

Gary said...


In Ithaca, the insulation value of the straw bale will be more important in the long run than the one-time carbon sequestration. But more to the point, having bright articulate people as first adapters of scalable technology is one of the best ways to get that technology into the mainstream. Figuring out how to lead the good life carbon neutral is no small task. Leading by example is a worthy endeavor. I'll be watching!

Anonymous said...

Stuart Staniford: But at an ethical level, I tend to feel that I'm only responsible for my own choices. If other folks choose to use any fossil fuels I may end up hopefully conserving, that's their responsibility, not mine.

That in nutshell is why our society is so ill-equipped to deal with climate change. No concept of collective guilt & collective responsibility.

Absolution can hardly come so cheap! In addition to asking ourselves individually how much of our total resources we devote to solving the problem & being willing to assess the competence of our attempts, we have to recognize that should we fail, the shame is on us too. We probably could have done more, we probably could have been more intelligent about it. We are our brother's keeper, after all.

Geoff said...

Eating locally under the current city-centric model is likely not more energy efficient or climate friendly, but surely that doesn't negate the idea that genuine local eating will beat both other methods hands down. It's not going to work for folks in the -urbs, but where someone is situated in a rural village or similar landscape then it would be an entirely different matter.

Wandering next door to drop off or pick up a box of food, or wheelbarrowing food down the road to a central market stall becomes a valid proposition. If half the town did that then everyone would be well fed for barely a hair above the production costs.

In the end the city interpretation of "local eating" is akin the city interpretation of most things. I appreciate that the great majority of western humanity resides in the cities, and so analysis of things like local eating needs to come from that viewpoint, but it's also important that people realise there is an alternative that does live up to the hype.

Stuart Staniford said...


I definitely don't have enough neurotransmitters to feel bad about everything that anybody's doing wrong anywhere in the world, so I think I'll stick to mainly feeling bad about my own failures and transgressions.

Spirited Raven said...

I live up the road from you in Interlaken (not that one of you Ithacans actually know the name or whereabouts of anything outside the city limits). I've built strawbale houses. I've built adobe. I've built rammed earth. Busted my hump for years like a donkey doing that kind of work for a wage. I'm a big advocate of re-localization and sustainability.

I have one rather large issue with your calculus. Why in the heck are you even building a new house?? There's plenty of houses out there to just move into and renovate if that's your fancy. You have all this smarmy arithmetic about carbon footprints. Why in the heck are you even building yet another house if this is important to you??

Blind suburbanite hypocrisy is a term that jumps to mind.

Stuart Staniford said...

Spirited Raven:

First off, please avoid personal insults in comments here. I'd be glad to hear you share your expertise and experience, but it's not going to work if it's laced with insults.

Second, we haven't made a decision about new versus retrofit (or indeed much of any decisions about detail or timing). I'm just trying to understand the factors that go into such decisions. That said, I wouldn't hesitate to build new if that seemed the best option - a bunch more houses are going to get built on this planet in coming decades regardless, and it would be good if more of them are zero energy.

Stuart Staniford said...

Also - I rode my bike round Cayuga lake last weekend, so I have managed to find Interlaken already :-)

Anonymous said...


Thanks for the link from Peak Oill Debunked. He got 779 comments on that one. Wow! I guess learning gardening is something for the long haul and for personal health and exercise in a scarcity economy as in the 30s USA( Waltons) where money was really short and in Russia where deliveries were incredibly inefficient due to central planning (ask my wife they had a big garden and got through the winter due to the potatoes and marmelade and picking lots of mushrooms in the woods and bottling them and taht in a city of 50,000-100,000 people.)

So I guess nowadays in modern efficient western countries a supermarket can't be beat. Maybe later that will be different and efficient local deliveries will be the norm when they have to really compete locally as thy will be only supply for the area and not as currently a hobby for upper middle class guilt ridden.

As far as feeding the grid and being carbon negative, not a bad idea. With feed in tariffs here in Germany and a couple solar cell panels on the roof I could make good second income and assuage my conscience all at the same time (after panels are amortized).

Anonymous said...

Hi, I came across your blog and thought you might like this initiative we are running; "Make Your Blog Carbon Neutral". If you get chance, have a look here:

Stuart Staniford said...


If I'm understanding the figures at your link right, my blog readership would currently generate about 7kg of carbon emissions/year. Given average US carbon emissions of about 5100kg, it seems like the blog is not the place to start :-)

Anonymous said...


Sounds like a form of cognitive withdrawal. Wouldn't you be in the top .05% or higher in smarts?

Not really asking anybody to feel bad, just work possible solutions that actually matter.

"Look folks, here's my little golden straw ark. This is how I feel good about myself" is kinda ridiculous. You are a blogger, Stuart, you gotta learn to take the heat. :-)

Stuart Staniford said...


"just work possible solutions that actually matter".

Look - the issue in the U.S. right now is that even pretty modest climate legislation doesn't have 60 votes in the senate. It appears likely to get worse rather than better in the next congress. I have no idea how to change that, and I doubt you do either. In the meantime, I propose to work on the stuff I can do (help explicate the science to anyone who actually cares what it says via this blog, and fix my own family's carbon emissions).

Alexander Ac said...


just make sure the house is fire resistant :-)

misfortune with climate change is that to climate it does not matter who emits the carbon. It is worse than smoking. The effect will be felt by everybody.


WwoofBum said...

It would be interesting to know what the "carbon value" of the energy invested in those bales is. Were they organically grown or conventionally (like, with lots of petroleum products). Were they harvested and baled by hand/horse or with diesel guzzling combines. What will it take to transport them from where they grew to where you will use them.

Stuart Staniford said...


Strawbales generally have very low embodied eg (eg here). Other components of the house have far higher - particularly the concrete foundation.

So one of the appeals of a retrofit is to avoid that embodied energy. There are people who have wrapped existing buildings in bales. Another possibility that occurs to me is to take an existing building in poor shape, tear it down, recycle the framing into the support structure of a new house, and reuse the foundation. That would also seem to minimize the embodied energy (if you consider the old house to be fully depreciated, anyway).

MisterMoose said...

My wife is after me to build a combination straw bale/hobbit house, at least partially underground, with passive solar, lots of insulation, etc. Our goal is to be completely energy independent, even if it requires a little more up-front investment than a traditional house. The price of energy will only go up in the future, so if we add a windmill, some solar panels, and some deep-cycle batteries, we'll be all set.

We already grow some of our own food in our square-foot raised-bed garden, so if we had a couple acres and some goats and chickens, we'd definitely be all set. Now all we need is a hundred thousand dollars to make this dream come true...

As far as eating locally or living off the grid are concerned, the main problem seems to be that you'd require a relatively large capital investment to be truly self-sufficient in either energy or food. Most people can barely afford to live paycheck-to-paycheck, let alone accumulate enough capital to build the infrastructure that would enable them to live for free off available sunlight.

As much as I'd love to see us all be completely independent, most of us just aren't going to be able to afford it any time soon. So, how many of us are going to have to starve and freeze in the dark after the fossil fuels run out because we couldn't afford to buy those solar panels or a couple acres of arable farm land?

On a slightly different tangent, is it possible to get a carbon credit for building an energy-efficient house? Maybe we could sell the carbon credit to Al Gore to help him assuage his guilt for being such a green hypocrite (you know, living in two mansions, and all...). I'm sorry for ranting about this, but people who preach to the rest of us about the necessity of saving energy and being carbon neutral, while they live a lavish, high-energy lifestyle, just don't cut it. Evidently these green missionaries believe that spreading the good word about the necessity of living a green lifestyle is so important that the rest of us benighted heathens should just forgive them for having to fly around in private jets.

So, Stuart, just being a blogger (who doesn't fly around in a private jet) is no big deal. Keep up the good work.

Unknown said...

Hi Stuart, (and greetings to Ithaca from rural Moravia).

I won't try to compete with your Physics PhD, but as part of my M.Sc. in Environmental Management (Dept. of Development and Planning, AAU, Denmark) I made a comparison analysis of a straw bale passive house (Load bearing Build from Big Bales (BBB) with a typical approach to passive house made from lime-sand elements and expanded styrofoam (LS/EPS). My study colleague, Fran├žois Gonthier-Gignac, made a Screening Life Cycle Assessment, and it's with background in these figures that I'll dare to question your conclusion.

Here's some of our findings:
"The construction stage presents more interesting facts. Figure 7.5 presents the relative importance of the impacts induced by each of the construction materials and processes. The negative figures represent the CO2 trapped in the wood and bales, and should be considered as neutral, as it is eventually going to be reemitted."

Francois extrapolation revealed that "during a 50 year life cycle of the building, the building works as a carbon 'sink' holding 5,8 ton of CO2 in the construction materials. The contribution of the construction stage for BBB is -19,2% for global warming, 26,8 % for Eutrophication, while it represent less than 10% for the two others groups of impacts. The end of life stage contributes mainly to global warming, with 17,3 % of the total load. The major contribution is the reemission of the CO2 trapped in the materials to the atmosphere. The other interesting point to notice is the negative contribution (-8,5 %) to nutrient enrichment –i.e. enhancement of environmental performance, caused by the reuse of the bales, modestly counterweighing for the overalls impacts linked to the construction stage."

This combination of both stages gives for BBB a negative value of -5,81 tons of CO2 equivalents, compared to 46,7 tons with LS/EPS. This is clearly the most important result coming out from this study. The negative value is however an irregularity that causes problem. The emissions should have been superior to zero, since the bales are supposed to emit back their inner CO2. The only way it can be explained is that a mistake was done when converting the straw to wood, or that the wood possesses more energy than straw for the same amount of CO2 released in the atmosphere."

The summary for the whole life cycle of the houses has been compared with the average annual contribution per person to each pollution category, for the year 1994.
Shared by its occupants, the impacts of the house (as it is defined in this study) accounts for 17,5% of the average annual contribution per person in the Global warming category which is certainly the most important results of this LCA.

In conclusion:
"The use stage is by far the most important stage in the life cycles of the study objects. It accounts for 81,7 % and more for all categories of impacts... The other important fact is that for BBB the use stage contributes around 100% of the global warming load."
"Summarizing, we found results to our query, and in this comparison the BBB showed a superior performance for both aspects of the question. This poses a central dilemma, to be solved in future studies: What if the inexpensive model would have been the model most harmful for the environment as often is the case? Due to this issue we recommend the (Platinum) LEED labeling over the Passive House concept."

I hope this helps bringing your numbers into perspective? It seems more important how your family spends its life inside your house (+ how you dispose of it after ‘end of use’), than your worries about the carbon used to build it. Add to this that with PV's on your roof (mentioned in your recent blog), pelton wheel or house hold wind turbine, you can in effect off-set the carbon which went into the building, by replacing carbon from 'fossile fuels' for years to come....

Max Vittrup Jensen
PermaLot Centre of Natural Building

Stuart Staniford said...


Thanks for commenting! At least as far as I can tell from your excerpt (I"m not sure I'm understanding the excerpts properly out of context), we are in broad agreement. I don't dispute that operating emissions are more important than embodied emissions - I just want to have understand what are the important factors in both (and whenever I do an operating energy calculation, I always get a bunch of people complaining that I've neglected the embodied energy).

Is your study online somewhere, or can you email it to me? (In general, I'd prefer not to have to do all these calculations, but just to find the answers easily available somewhere that I can link to, but not much luck so far).

Unknown said...

Hi again,

??? I gave up on trying to post it as I kept getting error messages! But somehow you got it; good!
I kept shaving it to make it fit the max. size of characters and must have by mistake shaved the link to the study:

And yes, I do agree to your notion of not re-inventing the wheel in manipulating figures...
Asides all of the fancy figures, LCA and embodied energy: The simple central point is that the carbon you calculate as consumed, is predominantly simply stored and can be ploughed back in to the soil. Such public message would support the promotion of SB building, rather than estrange some folks from it... ;-)

“Accounting is not an answer, but it gives some guidance, because we can look at other systems that do work and use these accounting methods as a crosscheck on our common sense. […] A study was done in Britain some years ago on recycled paper. They concluded it was easier to just put paper in an energy-efficient furnace and use it for fuel rather than recycle it. Ironically, using the permaculture strategy of using the paper as a sheet mulch technique to establish a food garden is probably light years ahead of either of those options. So the things that look very, very simple, rudimentary, even amateur, often when you use these more complete accounting methods, come up as the most energetically efficient.” David Holmgren, 2006

Enjoy the read, and again; credits for the LCA chapter goes to Francois; I was hardly involved in that part.

PS: I'd like to submit all what I tried to post, and a photo. Perhaps you're able to post it? If you're interested then please send me a mail with your real email address; mine can be found on our site.

Stuart Staniford said...


Thanks! I'll read your study.

My email address is available in the "About Me" part of the sidebar. However, the character limit in comments is set by Google and is not under my control - the simplest solution is to split your thoughts across multiple comments. Another alternative is to post them somewhere else and then link to them from comments here.

Unknown said...

Hi Stuart,

My family and I are also seriously thinking of moving from the Bay Area to Eastern Upstate NY. We've been looking at houses and land for about a year. I'd love to retrofit an older house as it is certainly true that the US is overhoused and in little need of more construction. However, of the decent number of houses we've seen, none have been suitably located or oriented for passive solar, wind break and other energy-conserving considerations. I had a fantasy that pre-petroleum houses might have been built more along ecological realities, but this does not appear to have been the case. According to locals, the folks of 200 years ago didn't know of any problem they couldn't fix by cutting down a few more trees. So I think you'd be very lucky to find an old place that has even a foundation suitable for bale construction. For one thing, bale construction in this climate requires very careful attention to frost and moisture transport so an old stone foundation might be a nightmare to retrofit. "Serious Straw Bale" has a lot of good technical info, if you haven't seen it.

As for the carbon capture aspect, yes, it's a tiny embodied offset. I'm trying to think in terms of the bigger picture of a more modest, lower-energy lifestyle. In this context, a super-insulated house made with local, low-energy and biodegradable materials makes sense. It's the right tool for the job, unlike the traditional houses. We're also trying to use as little technology as we can in the operation of the house. There's a risk of these projects becoming eco-chique instead of eco-simple, and we're trying to avoid this.

Best of luck!

Stuart Staniford said...


Thanks for your comment!

"eco-chique instead of eco-simple". I think I would characterize myself as "eco-rationalist" (for better or worse...)