Bale Out

Umbra on straw-bale homes 11

Dear Umbra,

Do you recommend building straw bale homes? And/or can you insulate an existing home with straw bales on the outside of the home and then finish it using siding, wood, or stucco? I wonder why this renewable, economical, and easily available resource is underused and undervalued ... am I missing something? What do you think?

Leni E.
Hollywood, Fla.

Dearest Leni,

Anyone who has seen a straw-bale home will not be making any of the traditional jokes about the Three Little Pigs. The plastered walls are filled with solid bales of straw at least 14 inches wide, and the houses sit heavily, though beautifully, on the landscape. They are not going to blow down with a simple huff and puff.

Not just for pigs anymore.

I have several happy friends with straw-bale homes, so I'm biased in favor of this system. Straw bale seems not only ecologically sound and cheaper than traditional construction, but fun to build (if you, like me, love plastering). So yes, I'm in favor of straw bale, but I'm no expert. If you are considering building with straw bale, it's vital to find local knowledge, first as to whether your climate would be a good choice for straw bale, and second to confirm local building codes. Modern straw-bale construction is not yet covered by most building codes.

There are two general ways to build a straw-bale home. One is to build a fairly typical post and beam frame, but instead of then adding studs, insulation, and sheetrock, one piles straw bales between the timbers. The wood holds up the roof, the straw fills the wall. In load-bearing straw bale, the bales themselves hold up the roof. In both cases, the bales are plastered inside and out with any of various plasters, ranging from local earth to Portland cement.

Straw is a cheap, renewable agricultural waste product -- leftover stalks from grains and seeds such as wheat or rice -- that has been used in building construction for centuries. Just to mention a few straw-y considerations, bales used in construction should be dry, sterile, and densely packed, and design of the house should keep water off the walls. The roof should have a long overhang, bottom bales should be a certain distance from the ground, and all exterior finish work should be watertight. If the house is well designed, moisture within the walls won't become a problem.

Dense straw is a good insulator, with an R value around 2.4 per inch -- putting an 18-inch-wide bale in the R-40s (fiberglass batts of insulation generally range from the teens through 30s). It also has high thermal mass, meaning it is slow to release and absorb heat, keeps buildings at a lovely consistent temperature, and is a good choice for passive solar homes.

I did find a little information on retrofitting an existing home with straw bales. It sounds complicated. The exterior walls will basically become at least 14 inches fatter, which means extending the roofline or building a new roof, maybe extending the foundation, dealing with how doors will open, building new window openings, negotiating the boundary between old and new walls, and other considerations. Basically, you can do it, but it may not be the most economical or even commonsensical approach to insulating your home.

In sum: Yay for straw. The internet is filled with informative, enthusiastic straw experts (one is The Last Straw). Go unto them, find a local group, and get any further questions more than answered.

Balefully,
Umbra

 

Yours is to wonder why, hers is to answer (or try). Send your green-living questions to Umbra.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

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  1. PermieWriter's avatar

    PermieWriter Posted 4:58 am
    22 Oct 2008

    The house that straw builtI've helped make a few clay/straw structures and it's wonderful stuff to work with and yields excellent results. Some folks tend to get caught up with straw bales. Make sure you look around. There's a whole continuum of techniques using the basic components of straw, clay, sand and water: cob, straw/clay infill, etc. Straw bale is overkill in most climates, but one of the other techniques might well work for your area. Don't forget the boots and hat!

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  2. RichardinKRV's avatar

    RichardinKRV Posted 5:23 am
    22 Oct 2008

    "not yet covered by most building codes"Modern straw-bale construction is not yet covered by most building codes.
    California has a straw bale building code.
    CALIFORNIA HEALTH AND SAFETY CODE

    SECTION 18944.30-18944.34

    Guidelines for Straw Bale Structures
    http://www.strawbuilding.org/tech/code/cahnscode.html

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  3. sje333 Posted 5:53 am
    22 Oct 2008

    humid climatesThe original question was asked by someone in Hollywood, FL.  I've always assumed that most of Florida is too humid for straw bale construction.  Am I mistaken?

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  4. Delay And Deny's avatar

    Delay And Deny Posted 7:31 am
    22 Oct 2008

    Perfect for what I'm thinking

    I've seen central washington land advertised for $29,000 for 40 acres!
    http://www.liveatgrandview.com/
    A straw house would be exactly right for me to homestead there and get away from light rail loving libs in seattle.

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  5. sustainablejohn's avatar

    sustainablejohn Posted 10:37 am
    22 Oct 2008

    fire safetywhat about fire safety? any codes out there on that?

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  6. PermieWriter's avatar

    PermieWriter Posted 4:08 pm
    22 Oct 2008

    FireI've seen video of someone taking a blowtorch to a rice straw bale. And it's pretty much impossible to get cob ignited. But I have no idea if this is reflected in the fire codes. Fire professionals, who have the most say in fire codes, are highly conservative about these matters. It's kind of amazing stick frame construction is still code legal, given their weight. Hmmm...

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  7. redambrosia99 Posted 2:04 am
    23 Oct 2008

    change the building codesI got to talk to a couple who built a very unusual house in the South Puget Sound area.  It wasn't straw bale, but it was built using traditional japanese temple building techniques.  The whole thing was built of wood.
    Anyway, in order to get their house approved by the building code folks they had to jump through all kinds of hoops.  At first they wouldn't let them build it.  But they were persistent and eventually they got to talk with the director and he approved it.
    The point being, building codes are only a problem if you let them be.  If you're polite and persistent, and share your excitement over your unusual house, you may just change the building codes.

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  8. BlackBear Posted 2:14 am
    23 Oct 2008

    FiresThe straw bale house designs I've looked at confirm that the walls are fire resistant and are classed with interior stairways in industrial buildings. Not to shabby for an organic substance.

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  9. slsessions Posted 3:30 am
    23 Oct 2008

    Consider one CAUTION!My husband and I just built a pumice-crete home.  He was our builder and was adamantly opposed to strawbale.  We live in NM and this is a pretty common choice for these parts.  There are LOTS of reasons to use straw bale.  The ONE reason we did not is because of plumbing in the walls.  You probably cannot guarantee that a pipe or PEX tubing will never break or leak, and keeping water out of the inside of your walls is essential for a straw bale home.  A water leak will require some major repair.  This is just one consideration to make when choosing a building material.  Pumice-crete has its drawbacks too, but we do have a beautiful, energy efficient home.

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  10. jtellerelsberg Posted 9:26 am
    23 Oct 2008

    Not necessarily a "waste" productHi Umbra,
    Though I am also a big fan of straw bale construction [and a conflict of interest alert: I work for Chelsea Green Publishing, publishers of books on straw bale construction (among other topics)], I'd hesitate to refer to straw merely as a "waste" product. Failure to return at least some decent quantity of straw to the soil from whence it grew would result in reduced organic matter and poorer soils--and so force growers to rely more heavily on artificial fertilizers and irrigation. At the current rate of straw bale construction I'm sure it's not an issue, but if there were a large increase in the number of straw bale buildings, we could face a serious trade-off issue between "eco" buildings and healthy soils.

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  11. fuentesdesign Posted 4:25 am
    25 Oct 2008

    straw bale retrofit applications and codesAs an architect specializing in straw bale design, we have done several different retrofit applications for bales and existing wood framed homes.  the most practical, cost effective way to insulate an existing home in my experience is with cellulose (recycled newspaper treated for fire resistance) blown into the existing walls either in empty, uninsulated cavities, or against existing fiberglass insulation.  This technique costs a lot less than putting in bales between studs at 16" centers, which i did for my own office/garage, or building a new foundation and roof as we are doing on a current "adobe wrap" bale project as the author mentions.  Bale walls with both earth and cement plasters have recently received fire ratings of 1 and 2 hours respectively, and local code officials (boulder, colorado) have accepted these ASTM tests for zero lot line projects we have completed.  Also, the international building code has provisions for alternative materials that are accepted by most local jurisdictions.  They require more documentation, but in our experience, are accepted.  the fire tests are available at
    http://www.dcat.net/about_dcat/current/ASTM_E119.pdf
    and more on our website on codes
    http://www.fuentesdesign.com/buildings/projects/why_straw ...

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