White Paper: Why Straw Bale Construction?


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Interview with Mark Schuneman of the Colorado Straw Bale Association, and Brian Fuentes, AIA


One of my clients, already committed to green construction, recently asked me why straw bale? While there is plenty of information online about the costs and benefits of the time tested technique of straw bale wall construction, I thought it would be appropriate to give a personal testimonial about the system based on my professional experience designing and building both conventional and straw bale buildings for both my current clients and those still trying to pick the best wall system for their home. I also wanted to explain why I believe it is the most beautiful and ecological option here in Colorado.

First off, rather than answering all the standard questions, such as "haven't you heard about the three little pigs?" I'm going to defer to the experts. If you are wondering about decomposition, termites, fire, moisture, plumbing, electrical, or if lawn gnomes will live in the walls, you can find a nice overview of the basics at the buildingscience.com.

More information is available at the California Straw Building Association Website.

Also, if you're stuck on the fire issue, please see this ASTM E119 testing available on dcat.net's website illustrating stuccoed strawbale walls perform better than similarly stuccoed wood frame walls.

A good overview about bale wall fire safety is available here.

There are one hour fire ratings for earth plastered walls,

and two hour fire ratings for cement based plaster walls.

Brian Fuentes' Experience with Straw Bales



Born and raised in Colorado, I never really realized how much I loved it here until I was swept away to the rainy University of Oregon in Eugene for architecture school. There I discovered straw bale construction, volunteering as a plasterer on the first bale house permitted in Eugene in 1997. I also discovered I couldn't take the rain, and wanted to move back to my 300+ days of sunshine, wide open front-range views, with some breathtaking expanses of native short prairie grasses still left, despite the ever-growing sprawl of vinyl-sided boxes into the landscape.

It just feels good



Before I get into R-Values, window details, and plaster options, I want to focus on how straw bale construction feels so good. From the first time I showed up on site as an idealistic architecture student, to standing atop a wall in the Colorado sunshine, covered in mud, smiling ear to ear, to the final inspections on the homes we are designing now, straw bale walls feel cozy and comforting. This is something you just don't get from a roll of fiberglass batt from home depot or even a more energy-efficient SIP (Structurally Insulated Panel). I believe this is what hooks most people on straw bale construction: they see the warm, soft light glowing around a wood window and suddenly a vision for the whole home grows out of this first feeling. They get excited about gathering local people together to hand plaster the walls and have a good time.

If we spend a third of our life sleeping at home, and perhaps another third living there, a home should really be a home to nurture, inspire and heal, and not just a real estate investment.

Feeling the Straw Bale Vibe



I never push people into choosing the straw bale wall system, when they are ready for it they are ready for it. If you are not feeling the vibe right now, you may want to skip this section of my essay and get to all the technology stuff and let your left brain get into it first.

I feel a connection with the living world when I'm working with bales. As a small child I always knew I wanted to be an architect and I was always building and sculpting. I remember the snow caves we used to build in the front yard after a big Colorado blizzard, and the amazing sense of accomplishment and wonder one experiences creating their own shelter. When these materials are literally from the land around you, the building ceases to be some foreign process that construction workers do, and start to come alive. A natural building becomes a book written, a work of art created, a gift given, and a child born. As a natural building grows around you, so does your soul. I have not felt this with the conventional buildings I have designed or built.



Now this last paragraph may not get you props at the LEED conference, where everyone is counting up green points, and I did lecture about this very subject at the last Colorado USGBC Conference, because I believe this is very important. This connection needs to happen in a very real and profound way, perhaps not for everyone, but for a large number of people, so buildings and the landscapes in peoples heads stop being an abstraction and begin to feel like an extension of themselves, like our families and relatives, suddenly taking care of the world and each other will start to seem less like a noble ideology and more like the best way to live for optimum health and happiness. In this mindset, I belive the decisions we will make about buildings will be very different.

There has not been enough research and documentation on human psychology in relation to the environment, especially the built environment, but if everyone in the industrialized world began to feel as some of us do, I believe there would be a wholesale shift in our approach to zoning, planning and designing our cities, towns and homes. Perhaps the one person who has been working his entire life on this very subject is Berkley Architect Christopher Alexander. It seems every practicing architect today I meet that I admire has read and been inspired by his book, A Pattern Language, or the latest and deepest of his explorations into the art of building and the nature of the Universe, The Nature of Order . Both of these texts bring to light the value of participating in the construction of your own home with your hands. I believe if more people had the chance to work on their own home, they would begin to understand the sheer weight of a building, the amount of effort and energy it takes to bring shelter into being, and in this, develop a deeper respect for their home, and the value it provides, and at what cost.

Just as educated America in the last 20 years has begun to realize the connection with eating healthy food and living better, so too I believe in some time we will look at strip malls the same way we do at the burgers and fries they sell there, simply unhealthy, and you can just feel it.

I believe straw bale construction represents a window towards a better, healthier world, and the people I have met who are on this path have a sparkle in their eye and a skip in their step. To them, the world is alive and magical, and the future an exciting opportunity. So I thank all of you for inspiring me and making me smile, and am honored you choose to work with me!

Bale R-Values, Window details, and Details for Tech Geeks



Moisture

Problems with straw bale are similar to those experienced with wood - they come from moisture. Either leaving the bales out in the rain, building a leaky window (which basically leaves the bales out in the rain) or not getting the bales high enough out of the ground or protected or sealed at the roof can lead to moisture which can lead to problems.

Therefore, here are three simple recommendations to keep straw bale walls dry:

1. Keep the foundation for the bale wall well out of the ground - 12" minimum. In areas where snow may pile up around the building, you will want to know how high it will pile up and if it may fall back against the wall.

2. Put the windows on the outside of the bale wall, flush with the exterior of the plaster so that if water gets behind the window, it drains on the front face of the plaster and not behind it. A lot of people still put the window in the middle of the wall, and there are good details for this that work, but you're adding 3 more joints that can leak, so its up to you to take the risk. See the photo below for how we like to see it done.



3. Keep the roof overhang 2' minimum for a 8' wall, 30" minimum for a one and-a-half story building, and avoid 2 story exposed faces if possible, or if not expect periodic maintenance to the plaster on wind-driven faces.

If you do these things and start with good dry straw, apply good plaster, and don't dump your bathtub onto the wall inside or hose it down outside, you should have a durable, healthy wall system.

Use heat recovery ventilation to provide fresh air to tightly sealed bale homes, pulling exhaust air from moist areas like kitchens and baths. This system should be designed by a knowledgable professional! Just as breathing is important to a healthy person, ventilation is critical to a healthy home. Don't underestimate the value of this.

R-Values of Straw Bale Walls - Only part of the story



The first question I get asked is always, "wow, what's the R - Value of straw bale?" When you think of a house as a living system, you think of the walls as not just insulation like clothing (r-value is a measure of thermal resistance), but also as thermal mass, like the water stored in our bodies, or the ocean, that has so much stored energy, that it takes time to heat up or cool down. This keeps the indoor temperature stable. Oak Ridge national labs is now working on a factor to give a numerical value for this, called the DMBS, or Dynamic Mass Benefit System.

This is the same way an all-mass strategy like adobe or rammed earth wall systems work. This mass helps regulate temperature, straw bale walls with 1" to 1.5" of plaster weigh five times what a typical 2x4 wall with fiberglass weighs. Conservative tests indicate an R-Value for a typical bale wall of about R-30, but when you factor in the thermal mass, and that if you can just get enough mass to make it through the cold night until the day comes and the air temperature increases, then you have a system which performs much better than the same R-30 system such as a SIP (structurally insulate panel) with less mass. All this is explained in detail in this report at the ecobuild network website.

The other energy part of the pie, which people are only starting to talk about, is embodied energy, or the energy required to produce, deliver and install the insulation. Compared to other forms of insulation, such as polystyrene SIPs, or polyurethane SIPs, cellulose is much less (treated recycled paper). These are compared in embodied energy per unit of insulating value in this Building Green Article. Straw bale insulated buildings would be even less, although they are not specifically mentioned in this article, because the grain would have been produced anyway, and often the straw is either burned or tilled back in to the soil. This supports local farmers, and we should pay them more for well made, construction ready bales. Please contact us if you are interested in making a few extra bucks by selling us some well-built, local bales! Therefore the only embodied energy in the straw itself would be from the energy to ship the bales to the site. If you're as cool as the people in Portland that help people move with their bikes instead of a truck, you could have yourself some embodied energy free insulation!

The bottom line is most homeowners discover their bale house is thermally comfortable, and changes very little with the crazy Colorado weather swings we have, making it comfortable year round. Bales and plaster mass also make for amazing acoustical insulation. Without digressing into acoustical design theory, lets just say the combination of solid heavy mass and light, air filled straw makes for a wall that absorbs both low and high frequency sound. Odisea builds bale sound walls here in Boulder for this reason. Bales make sense on many levels.

Earth Plaster


expert earth plaster applicators can be found anywhere...

Dirt. You played in it as a kid. Here is your chance to do it again. All plaster systems for straw bale walls require 3 or more coats, so earth is cheap and local, has the least embodied energy of all the plasters, and is the best choice in my opinion. It feels buttery in your hands, smells good, and you can give yourself a facial while you work. It also seems to balance and store moisture really well, and cleans the air a bit. I need to do some research on this to see if anybody has done anything scientific, because this is just my experience working in our straw bale office. The Last Straw Journal Website has more information on earth plaster. Ryan Chivers has developed a system/recipe we used on our office and one of our nicest projects here in boulder that is, as we say, 'bomber.' Meaning bomb proof. Now bombs don't sheet water down your wall, so you will need a Lime Plaster finish Coat on the outside to prevent excessive maintenance, unless you have super huge overhangs or covered porches that will keep 90% of any wind blown moisture off the walls. Keep reading.

Lime Plaster


General Contractor/Builder Jeff DeMeyer (left) applying the lime finish coat over earth base coats at the Strawbale Studio by the Park in Boulder

This stuff is as old as the hills, and is a living plaster, like earth, meaning you can always repair it and mend it with another coat. There is the hydraulic stuff from france that is just as good as the wine and cheese, and then you can get local stuff and slake your own, meaning you soak it in water for as long as possible and let it turn into nice soft putty for plaster. This stuff you can use inside and out, as a finish coat or as the whole plaster system. This is my second favorite plaster type and is used on the buildings we design as a finish coat on the outside over 2 -3 base coats of earth plaster for durability. Now there are more ingredients in the recipe here, so please don't just go out and buy some lime and start throwing it on the walls.

Portland Cement Based Plaster

Since we live in the industrial age, everyone already knows about good ol' C-ment and concrete. Its strong, takes a lot of energy to make, and is hard to get right now with China buying it all up. If it cracks, you have to patch it like any normal stucco home, and it will look kinda bad. This stuff is okay, but the third choice in my mind for folks who just are still afraid of the natural plasters. Use it for foundations, where it seems to be the best in class.

Gypsum Plaster

We even have a town in Colorado called Gypsum! Its what's in drywall, and is a nice finish plaster on the inside mixed with some good ol' dirt. It is the most like drywall for people who want a wall that behaves like the industrial age material we have everywhere else. You can stick pins in it real easy and it nails better than earth or lime, although wood screws work great into any plaster system except concrete. Lime is also a little harder.

A la Carte

There are clay paints, clay gypsum mixes, and more receipes than my grandmother has for gingerbread, so read Dan Chiras' The Natural Plaster Book, or hook up with your local Plaster Master if you want to know more.

Plastering is fun, but can be expensive if you hire it out. It may not be the cheapest way to build a house, but dirt cheap isn't the point (although the dirt itself is really cheap, its the labor you've paying for so call up your cousins). If America bought houses like they bought cars, there would be a lot more straw bale houses around.

Quality over quantity is the mantra here. A smaller house will allow you to focus on all the other things in life you like to do. After spending the last 4 years in 325 square-feet of sweet perfection, I highly reccommend it.

Conclusion

I haven't come to any conclusions in life, except that I like to ride my bike. So to sum it all up, from the nearest I can tell, straw bale wall systems are fun to build, good-for-you/good-for-the-planet wall systems which when built correctly heal the soul, warm the heart (as well as the rest of your body) and inspire the mind. It can last as long as anything out there, and when you're done with it you can throw it out without hurting Mr. Environment or Mother Earth, or however you prefer to think about it.

Obviously, just as having good boots and a warm hat are also critical to staying warm in the winter, foundation details and roof details are also really key to good overall building performance, which is just one more reason you hire a qualified professional. : )

Hope this helps,

brian f. (fuentesdesign home)


left to right, Ian Smith (Odisea Engineering), Fuentes, Taryn Hanson (who has helped so much on every project, we're going to have to do her house for free), and Mr. Ryan Chivers.