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Straw-Bale Walls

Straw bales have a higher R-value than other common natural building materials

Posted on Jul 29 2011 by user-756436

Do you want to build your home out of natural materials? If so, you can build your walls with adobe, cob, cordwood, rammed earth, or wattle-and-daub. Although all of these walls have a long history, their thermal performance is poor. If you want a well-insulated wall, one natural material is the clear winner: straw bales.

A 23-inch-thick straw-bale wall has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about R-33. Moreover, since virtually all straw-bale walls are plastered on both sides, these walls are relatively airtight.

If you are an owner/builder with lots of time on your hands, and you want to build your walls out of natural materials, straw-bale construction makes a lot of sense.

Nebraska roots

The first straw-bale houses were built in Nebraska in the late 19th century. (I'm proud of this Nebraska connection. Both of my maternal great-grandparents settled in Enders, Nebraska, in the 19th century, while my paternal grandmother grew up in a sod house in South Dakota.) According to Bruce King, the author of Design of Straw Bale Buildings, the oldest standing straw-bale building in the world is the 108-year-old Burke house in Alliance, Nebraska.

Many people confuse straw and hay. Hay is dried grass — the same stuff that your lawnmower spits out. Hay is used to feed cattle, horses, and other farm animals. Straw, on the other hand, consists of the dried stems of grain plants — for example, wheat, oats, barley, rye, or rice. Since hay is more vulnerable to rot and mold than straw, hay bales should not be used for wall construction.

Straw is often sold for use as stable bedding. However, in areas of the country where the supply of straw exceeds the market demand, straw is sometimes burned. The price of straw varies widely by region; in areas of the country where grain is commonly grown, a bale of straw is cheaper than a bale of hay. Elsewhere, however, straw often costs much more than hay.

Straw bales come in two sizes: a two-string bale measures about 15 in. x 18 in. x 36 in., while a three-string bale measures about 16 in. x 23 in. x 46 in. Either size can be used for wall construction. When used to build a wall, straw bales are usually stacked flat (not on edge), so a wall made from two-string bales will be about 18 in. thick, while a wall made from three-string bales will be about 23 in. thick. Of course, the thicker the wall, the higher the R-value.

All types of straw — including wheat straw, barley straw, oat straw, rye straw, and rice straw — are suitable for wall building. If it’s available locally, rice straw is often preferred, since it is said to be more resistant to decay than other types of straw.

Every straw-bale wall needs to be plastered on both sides. The plaster serves many functions: it is a structural element that increases the wall’s load-bearing capacity; it improves a wall’s fire resistance; it helps keep the straw bales dry; and it keeps out rodents. A wide variety of plasters are used on straw-bale homes, including lime-based plasters, cement-based plasters, and clay-based plasters.

Straw-bale walls are strong and durable. According to Bruce King, “Load-bearing straw-bale walls in Pensacola, Florida, easily survived a powerful hurricane — before they had been plastered. In short, the empirical evidence to date tells us that straw-bale walls of conventional dimensions are not appreciably affected by high winds.”’

Walls must be kept dry

The biggest enemy of a straw-bale wall (or, for that matter, of a wood-framed wall) is moisture. It’s vitally important to keep liquid water out of a straw-bale wall. To accomplish this goal:

  • Straw bales must be dry when purchased.
  • Straw bales must be kept dry during construction.
  • The foundation must be raised above the surrounding grade.
  • The first course of straw bales must sit higher than the floor.
  • The roof must have generous overhangs on all sides.
  • Decks and patios must be designed to minimize splashback.
  • Windows and doors must be properly detailed and flashed to prevent water entry.
  • Homeowners must avoid using sprinklers near exterior walls.

Hard experience has taught straw-bale builders the importance of impeccable moisture detailing. Building scientist John Straube told me one story of a straw-bale failure: “Years ago, I investigated an Arizona project with a moisture problem. It was a straw-bale house with a low-slope roof and no overhangs. There was a parapet with a rounded top and vigas — projecting beams that penetrate the walls. Water entered the wall at the top of the parapet, accumulated, and ran down the wall and found the vigas, where it leaked in. Most of one wall had to be rebuilt because of moldy straw bales.”

Like Straube, straw-bale expert Andrew Morrison emphasizes the importance of good detailing to prevent water damage. “Many builders can tell you horror stories about broken pipes and blown washing-machine hoses,” Morrison wrote. “Imagine the repairs if the leak flooded into a wall made of straw bales. The bales could wick all of the water right off the floor and up into the walls. It is possible that the walls would not be able to sufficiently dry out and would therefore be ruined and need replacing. That is a catastrophic repair and it is exactly why we do not place water pipes in the bale walls and why the bales never sit directly on the ground.”

To understand what can happen to a straw-bale wall without adequate detailing to prevent water entry, it’s worth checking out photos of a failed free-standing straw-bale wall in Tucson, Arizona — a city with a relatively dry climate.

Of course, water entry can do as much damage to a wood-framed wall as a straw-bale wall. Straube told me, “I’ve seen more regular houses rotting that straw-bale houses rotting. Of course, that’s because there are more regular houses. The thing that has kept straw-bale homes out of the ditches is that most straw-bale practitioners pay close attention to these moisture issues. You can manage these moisture risks with experience and prudence. Straw-bale builders are much better than the average yahoo builder who throws up a stick-built house.”

Compared to bulk water entry, other forms of moisture transport rarely cause problems in straw-bale walls. Of course, an air leakage path through a straw bale wall could lead to condensation, so standard attention to air-sealing details is important. However, vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. is very unlikely to cause any problems.

Load-bearing or infill?

There are two basic types of straw-bale buildings: buildings with load-bearing straw-bale walls (also known as “Nebraska-style” buildings), and post-and-beam buildings with straw-bale infill.

Before choosing to build a Nebraska-style building, you need to overcome two hurdles:

  • Verify that your local building official will approve a Nebraska-style straw-bale building; and
  • Develop a plan to keep all of your straw bales dry during construction.

“Keeping the bales dry during construction may not be a problem in Arizona,” says Straube. “In Vermont, it is.” If you have no code barriers and you live in a dry climate, a Nebraska-style building may make sense. Most such buildings are limited to one story.

Compressing the wall

Before you can plaster a Nebraska-style building, you have to consider the problem of bale settlement. After a straw-bale wall is built, the weight of the upper bales causes the wall to settle. If you wait a couple of months, you’ll find that the wall has settled by 1/2 inch to 4 inches.

If your construction schedule doesn’t allow you to wait a few months before plastering your walls, you can “pre-compress” your walls. There are several wall-compression techniques:

  • According to Bruce King, “Builders have found … that [settling is] drastically reduced if bales are emphatically stomped into place both downward and against adjacent bales.”
  • The bucket of a front-end loader can be used to compress the wall.
  • The wall can be cinched down with polyester packing straps or fencing wire that passes through a curved plastic conduit that is positioned in the concrete footing under the wall. The packing straps or wire pass over the wall top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate., and a ratchet device is used to cinch the strapping.

Advantages of the post-and-beam approach

Builders in damp climates usually choose to build a post-and-beam building with straw-bale infill. The main advantage of this approach is that it is possible to install the roof before the straw bales are delivered to the job site, greatly simplifying efforts to keep the bales dry.

If you live in an area of the country where straw-bale homes are still rare, you may find it easier to get approval from your local building official for a post-and-beam building than a Nebraska-style building.

More design issues

Once you’ve decided whether you’re building a post-and-beam building or a Nebraska-style building, the design process can begin. To ensure good roof overhangs on all four sides, a hip roof makes more sense than a gable roof. Straw-bale walls should never include a vapor barrier on either side of the wall.

Because straw-bale walls are quite wide, the easiest foundation option is the thickened-edge concrete slab on grade. It’s a good idea to leave rebar pins sticking out at the perimeter of the foundation; you want to have at least two rebar pins per bale. (Instead of rebar pins, some builders install projecting spikes in the parallel 2x4s used to create a “toe-up” under the first course of bales.)

Construction tips

Builders use a variety of techniques to raise the first course of bales above the level of the slab. According to straw-bale expert Mark Piepkorn, “In slab-on-grade applications, a [concrete] bale-wide curb can be poured integrally to raise the bales above floor-level. Similarly, a ‘toe-up’ between the floor and the first course of bales is becoming increasingly common. The toe-up is a set of parallel rails at bale-width, generally wood ..., set with anchor bolts to the slab, or ram set, or screwed to the decking. The area between these rails can be filled with anything providing a capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. break, such as crushed gravel. … Besides lifting the bales off the floor, this technique provides a convenient nailing strip on the exterior for the stucco reinforcement and an aluminum drip edge. It’s also been suggested that the interior rail can be inset from the true edge of the wall to form a wire chase behind baseboards.”

The second course of bales is offset from the lower course by half a bale length to create a “running bond” pattern. To cut a bale in half, each half bale is tied together tightly with baling twine before the bale's strings are cut. If necessary, a large wooden mallet — a “persuader” — can be used to nudge bales that are out of plumb back into position.

Bales are often anchored to lower courses with wood stakes (usually 1x2s about 36 in. long), bamboo stakes, or rebar. However, according to Laura Bartels, a builder and green-building consultant in Carbondale, Colorado, many straw-bale builders have concluded that staking bales is unnecessary.

Plywood or lumber window bucks are used to establish window rough openings. Straw-bale builders should research window-buck methods used by other builders before designing their own window bucks.

Straube advises builders to keep a fire extinguisher handy. “You need to beware of fire during construction, since there will probably be a lot of loose chaff and cut-up straw on the job site,” he says. Once the walls are plastered, however, the fire risk is minimal.

At the top of the wall, builders of Nebraska-style homes usually install a wide wooden top plate or a concrete bond beam. The roof is framed conventionally, using rafters or roof trusses.

Window flashing and plaster

Because liquid water is the enemy of a straw-bale wall, windows should be installed as “outies,” not “innies.” Window sills must be carefully detailed. “The fundamental requirement [for window sills] is that there be an outer layer of claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. , with a drainage gap below and a waterproof layer below that,” says Straube. “You also need an opening to let the water out. You can use a Benjamin Obdyke product to create the drainage gap, or in a dry climate, you can use two layers of building paperTypically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt.. You also need some type of flashing with a drip edge and an exit slot for the water.”

Once the walls are up (and, if necessary, compressed), it’s time to plaster. While some straw-bale builders apply plaster directly to the straw bales, Straube recommends attaching chicken wire or wire lath to the bales before plastering. “I want metal mesh in the plaster, even if it’s only light chicken-wire, for a bunch of reasons,” says Straube. “The main purpose of the mesh to keep the crack sizes small.” Chicken wire is attached to the bales using U-shaped pins poked into the bales or wires that go all the way through the bales; this is done with the help of a tool called a “bale needle.”

Laura Bartels advises against the use of chicken wire. “We usually avoid the use of metal meshes unless required structurally,” says Bartels. “Chicken wire or stronger is required in high seismic areas, but other than those cases, you will mostly find that plaster prep involves reinforcing at corners, material transitions and over framing or other materials.”

Traditional plastering techniques require three coats of plaster: a scratch coat, a brown coat, and a finish coat. The total thickness of the plaster is usually between 1 in. and 1 1/2 in.

If you don’t want a stucco exterior, you can install any type of siding you want. However, it’s essential that the exterior side of the straw-bale wall be plastered, even if you later install furring strips and wood or fiber-cement siding.

“It’s very easy to put furring strips on,” says Straube. “One way is to install a scratch coat of plaster, then install your furring strips screwed to the stucco, and then install another coat of plaster between the furring strips. A better way to do it is to install two coats of plaster and then install the furring strips, shimming as needed, with Tapcon screws. The plaster will hold the Tapcons.”

Mark Piepkorn likes the idea of a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap on straw-bale walls. “The general consensus of experienced and knowledgeable straw-bale builders indicates that external cladding [over a rainscreen gap] will perform better than stucco alone in nearly all circumstances, if properly implemented,” Piepkorn writes.

Some builders install 2x4s on the inside surface of straw-bale walls to facilitate attaching kitchen cabinets; these 2x4s can be through-bolted with 1/2-in. threaded rod. (You’ll need a large plywood washer on the exterior of the wall). Another approach (one mentioned by Bruce King) is to attach cabinets to wooden stakes that are pounded into the straw before plastering.

Wiring and plumbing

Any wiring embedded in a straw-bale wall is best installed in conduit. “Conduit can be let into grooves carved by chainsaw or ‘weed whacker’ into the straw surface,” King advises.

It’s best to avoid any plumbing pipes in a straw-bale wall; in a pinch, it’s always possible to build a chase or a faux framed wall for the plumbing.

Code issues

A full survey of the status of straw-bale building codes is beyond the scope of this article. Code requirements change all the time, so it’s best to research the current situation in your local jurisdiction.

The first straw-bale code in the U.S. was adopted by Tucson, Arizona, and Pima County, Arizona, in 1996. California followed Pima County's lead a few months later with statewide guidelines for straw-bale structures.

In 1996, New Mexico adopted a straw-bale standard that (unlike the Arizona code or California guidelines) does not permit load-bearing “Nebraska-style” walls. The New Mexico code requires straw-bale buildings to include a post-and-beam frame.

Several cities with active green-building communities adopted straw-bale codes in the late 1990s; among them were Austin, Texas (1997) and Boulder, Colorado (1998).

Disclaimer

This introductory article is an attempt at an overview of straw-bale construction methods.

It should not be considered a guide to construction, so if you are planning to build your first straw-bale house, be sure to research the topic thoroughly, using some of the many available books, Web sites, or instructional courses.

Does a straw-bale house make sense for you?

If you are an owner/builder with plenty of time and access to inexpensive straw, a straw-bale home can be an affordable method of construction.

However, straw-bale construction is relatively time-consuming; installing metal lath and plastering goes slowly. If you are hiring a contractor, you can expect a straw-bale house to cost more than a stick-built house.

Last week’s blog: “All About Larsen Trusses.”


Tags: ,

Image Credits:

  1. Peter Lenardon
  2. Laura Bartels
  3. Heron Construction and Straw & Timber Craftsmen Inc
  4. Sandra Cohen-Rose and Colin Rose
  5. Peter Leth
  6. Kelly Lerner, www.one-world-design.com

1.
Jul 29, 2011 11:52 AM ET

mudsill
by stuccofirst

insulation where the sill meets the concrete?


2.
Jul 29, 2011 12:15 PM ET

Response to Shane Claflin
by user-756436

Shane,
Look at the photos.

Image 3 shows 2x4 bottom plates installed on a slab-on-grade foundation; rigid foam has been installed between the 2x4s to provide insulation.

Image 4 shows the use of Perlite for the same purpose.

If you are worried about air sealing (rather than insulation), use any conventional sill-seal product between the 2x4 toe-up plates and the concrete. Sill seal can be supplemented with caulk.


3.
Jul 29, 2011 3:22 PM ET

Many thanks
by yyk7n5Ygtp

Thank you very much Martin for this very interesting post.

I'm from Sonora Mexico (not too far from Tucson) my parents just bought a nice lot where we're planning to build a small country house and we're looking over the possibility of wheat straw-bale and adobe as our main building materials.

I really enjoy your blog and this entry on particular was trully motivational. I work as an environmental consultant/building-energy-modeller and I don't really have that much building experience so I hope it does not bother you much if I directly ask for some book/web-site recommendations.

Finally, I'm also a devoted Passivhaus fan (I got the opportunity of touring the German houses on the Solar Decathlon Europe competition and I was delighted), so, is the concept of an adobe/straw-bale Passivhaus in the Sonoran desert just plain crazy?

Best regards!


4.
Jul 29, 2011 3:41 PM ET

Response to Mauro Contreras
by user-756436

Mauro,
Thanks for the kind words.

If you are interested in more information, you should check out the books and Web sites listed in the "More Information" box above.

As to whether it's possible to build a straw-bale Passivhaus in the Sonoran desert: I don't know. Hot-climate Passivhaus details are still being developed -- cold-climate Passivhaus examples are far more common -- and I'm not a certified Passivhaus consultant. You'll have to hire a consultant to get a full answer to your question.


5.
Jul 29, 2011 8:13 PM ET

Corrections and Clarifications
by hUd6rCjJMg

While addressing the preference for infill straw bale (SB) in wet climates and the fact that most codes no not allow load-bearing SB walls, much of the description of construction methods and techniques is relevant only to structural SB construction in dry climates. For instance, you say "at the top of the wall, builders usually install a wide wooden top plate or a concrete bond beam." This is necessary only for load-bearing walls. A timber frame already has a rafter plate.

For SB infill, bales can be laid either flat or on edge. There are advantages and disadvantages to each, but the overall R-value is about the same. To cut a bale in half, your instructions are backwards: each half bale is first tied together tightly with baling twine or plastic pallet binders and then the bale’s strings are cut. Otherwise the compression and density is lost.

The easiest foundation option for infill SB is not "the thickened-edge concrete slab on grade", which requires a toe-up and capillary break, but a conventional foundation to support the timber frame, with a wooden floor deck extending out beyond the foundation to support the exterior SB thermal envelope. This puts the bales on wood rather than concrete and raises them well above the exterior grade to avoid the splashback that is inevitable at this most problematic of areas.

"It’s a good idea to leave rebar pins sticking out at the perimeter of the foundation …many straw-bale builders have concluded that staking bales is unnecessary." Not only unnecessary but dangerous in a wet and cold climate, as this will almost certainly result in condensation on the steel in the middle of the bales.

I believe you've misapplied Straube's quote to window sills, since he's addressing cladding drainage systems. “The fundamental requirement [for window sills (sic)] is that there be an outer layer of cladding, with a drainage gap below and a waterproof layer below that,” says Straube. “You also need an opening to let the water out. You can use a Benjamin Obdyke product to create the drainage gap, or in a dry climate, you can use two layers of building paper. You also need some type of flashing with a drip edge and an exit slot for the water.” In fact, the exterior plaster is keyed directly into the bales and must be in contact with the straw to act as fire-proofing, rodent-proofing and moisture barrier. No housewrap or drainage mat should be used between straw and plaster. Flashing is needed wherever the plaster meets another material, and window sills need to be sloped and include a drip groove. Wooden cladding requires only a slight gap outside of the plastered bales created by the furring strips, which should not be screwed to an earthen plaster but attached in a more secure manner – either to framing or embedded stakes or tied through the bales .

"While some straw-bale builders apply plaster directly to the straw bales, Straube recommends attaching chicken wire or wire lath to the bales before plastering." Again, this may work in a very dry climate, but everywhere else it's best to avoid metal on the exterior.

"Laura Bartels advises against the use of chicken wire." For transitions over framing or other members, burlap soaked in clay slip works well. There are also fiberglass mesh products. Chicken wire is sometimes used under the interior (warm side) plaster to create curves at window and door returns.

As for other, more reliable, resources, I would suggest looking for a soon-to-be-published book by Jacob "Deva" Racusin (the instructor for the Natural Building Intensive and Straw Bale classes at Yestermorrow) on the Chelsea Green imprint. Though I am not a straw-bale builder, I edited several chapter of Deva's book and have consulted with him on his projects. Deva is also writing up the results of energy auditing and blower door testing on a number of northeastern SB homes. The primary challenge for SB builders in a cold climate is air-sealing details. Wrapping a timber frame, particularly one with knee braces, presents many transitions which require very careful detailing. It's at those transitions and between walls and ceilings where air leaks and consequent moisture accumulation is often found.


6.
Jul 29, 2011 9:19 PM ET

Mauro, Straw bale
by user-945928

Mauro,

Straw bale Passivhaeuser are totally feasible, even in the Sonoran desert. There are a number of straw and rammed earth Passivhaeuser - and even a SIPs-esque panelized system w/ insulation and panels made from straw (like agriboard).

You shouldn't need triple pane, nor too much insulation if designed properly. Detailing w/ rammed earth or adobe will be a little trickier, as you'll mostly likely need to add insulation (so in effect, a kind of sandwich wall as done by the SIREWALL folks).

My old boss worked at TU Darmstadt where the solar decathlon projects were built. Some really great resources at that uni. In terms of design, the 2007 version was much nicer.


7.
Jul 29, 2011 9:45 PM ET

Edited Jul 29, 2011 9:48 PM ET.

Clarifications
by user-968893

I have been building strawbale buildings for 13 years on the West Coast and mostly in Vermont. I applaud Martin for covering this great building method, but I am afraid I would not recommend this introduction. I would agree with most of Roberts corrections and begin by saying that any into to SB that does not clarify a climate is not worth reading. The details for Vermont vs. Arizona are very different. On top of this there were some major omissions such as the discussion of material to use for plastering, as well as the good hat and good pair of shoes rule that dictates a min. 18" from grade separation for a SB wall and the same overhang if not more depending on the exposure. There are some universal best practices, but using cement stucco plaster in Vermont for example, is a recipe for disaster.
And as much as I respect Straub's work, I would not refer to him on SB construction practices. I find that he generally has a decent understanding of the building science of SB's but it seems that he hasn't been around many projects.
My recommendation to anyone looking to build with Strawbales would be to find local builder swith SB experience and look at their work, watch a project being built, and talk to other builders from the area. A strawbale "expert" in Oregon could cost you 15 grand in plaster mistakes on a project in Maine. I have seen it happen.
The most exciting development in SB building for me is the development of high performance detailing that has developed over the past several years in cold climates. Strawbale structures have achieved PassiveHouse standards in other countries. Achieving PH air tightness will be quite difficult with the plaster method described in this article. There are many ways to build with SB that involve stud framing and proven air barriers that will make it much easier to achieve the PH standard, and more affordable.

It would be great to see another article on SB focusing on cold climates, with a little more research. There is a professional trade network called Natural Builders Northeast, (www.nbne.org) that is a great resource.


8.
Jul 30, 2011 3:45 AM ET

Edited Jul 30, 2011 3:51 AM ET.

Response to Ben Graham and Robert Riversong
by user-756436

Ben,
You wrote, "The details for Vermont vs. Arizona are very different." I certainly agree with you that climate matters -- I have been emphasizing that point for many years. (Of course, the same could be said about conventional construction details. Even for a stick-built home, details in Vermont are quite different from those in Arizona.) Thanks for reminding readers that the same principle applies to straw-bale construction.

I'm a little surprised at one of your points: "There were some major omissions such as ... the good hat and good pair of shoes rule that dictates a min. 18 in. from grade separation for a SB wall and the same overhang if not more depending on the exposure." In fact, I mentioned those details when I wrote, "It’s vitally important to keep liquid water out of a straw-bale wall. To accomplish this goal, ... the foundation must be raised above the surrounding grade, ... [and] the roof must have generous overhangs on all sides." I'm not sure what I could have written that was stronger than the phrase "vitally important."

This introductory article did not allow a full discussion of plaster specification, which is why I directed readers to the sources provided in the "More Information" box. Thanks very much for referring readers to Natural Builders Northeast.


9.
Aug 2, 2011 8:37 AM ET

Response to Mike Eliason
by yyk7n5Ygtp

Thanks for the feedback!

The houses from TU Darmstadt were awesome, in the competition in Madrid last summer my personal favorite was the house from HTW Berlin.

Cheers!


10.
Aug 3, 2011 3:57 PM ET

Ok call me crazy!
by user-974013

I love this! I have herd of it but never actually gave it much attention. I need to do this at least in once in my life.
Here is where everyone will hate me but, what about 2 inches of spray foam on the exterior, than coat it with stucco/mud/whatever??? This will act as a vapor retardant and with the stucco over top of it I think the straw will be plenty protected.
I get this is a total natrually green thing, BUT a little nudge from some spray foam would make this rock!
I am totally on board with this, I just do not know if we have a big straw inventory here in NJ (there are still lenty of farms in the area plus with PA so close...)
I do not know what do you guys think?
Thanks for the cool article!


11.
Aug 3, 2011 10:03 PM ET

Edited Aug 3, 2011 10:17 PM ET.

Good intro
by seaweedsl

I'm also a builder with bale experience in the Southwest. I applaud your condensed but fairly thorough introduction. The one error that stood out for me is that we have installed bales on edge in order to save wall width and it works fine, with some issues having the strings out.

I'm a big fan of load bearing and wish to promote it. It's much easier and more "elegant" way to build. I also build adobe and they both seem much more suited and actually stronger in the load bearing form. Still, I agree, the post and beam approach is often worth all the extra hassle for the convenience in the building process. Tradeoffs.

About pinning. Perhaps the trends have changed, but we found exterior pinning with bamboo (or...rebar!) to much stronger and more workable than interior pinning. Whether pinning is necessary is debatable, but it does rigidify the walls before plastering.

While it's apparent that Ben and Robert have very solid experience and/or information and well developed opinions, I did not find the faults they did, perhaps because of the region I've worked in. In any case, you did cover the critical "hat and boots" well, I thought. And I'd like to know more about why stucco is a recipe for disaster in the Northwest. I suppose it's just too wet too often? Snow against the walls? Also, is there documentation about stucco/chicken wire actually attracting moisture or is that an idea going around? I've missed that while living out of country.recently.

Also, about flashing: Certainly all the straw should be plastered, but flashing can still be applied. I like to detail windows by smooth mudding around them up to the finish plane during prep, then, once dry, applying an adhesive flexible membrane flashing right to the mud around the window. It sticks and stays on long enough to finish, anyway, Expanded metal lathe goes over that for the plaster. This has worked well in the SW, allowing innies without moisture issues. It does require careful attention to the detail.

Really, that's the final point about Straw I'd like to make. It's been promoted in the past as a do-it-yourself, easy-up kind of approach, but I find that deceptive. Walls can go up quickly , but straw is very detail oriented and can be a recipe for disaster if you or your builder are not well aware of the need for intelligent attention to the details. And lots of them. Not a piece of cake, not cheap, but a great material when done right.

Look forward to more articles about advances and differences in detailing SB for different climates.


12.
Aug 4, 2011 6:13 AM ET

Frank Bovio
by user-756436

Frank,
I'm glad to hear that you are enthusiastic about straw-bale walls.

I don't recommend installing spray foam on the exterior of a straw-bale wall, because the foam will reduce drying to the exterior. In the case of a flashing failure that allows moisture to enter the wall, you want the wall to dry quickly in both directions.


13.
Aug 4, 2011 6:19 AM ET

Edited Aug 4, 2011 7:13 AM ET.

Response to Steven Lewis
by user-756436

Steven,
Thanks for the useful tips and kind words.

I think it's fair to say that straw-bale builders are a fairly opinionated lot. Different techniques have arisen in different areas; some of these differences are due to differences in climate, while other differences simply reflect local practice that has solidified into dogma over the years.

Writing about straw-bale construction is difficult, because a few builders are likely to contradict almost any statement. In any case, thanks for sharing your techniques.


14.
Aug 6, 2011 8:08 AM ET

Structural issues
by KHWillets

Thanks for the article. I've been reading the links as well.

That Building Science article is helpful, but it leaves me with a few questions about the structural aspects for load-bearing walls:

If 95-99% of the load is carried by the plaster skin, why does the wall need to settle or be compressed before plastering?

What kind of plaster details are needed to transfer the load at the sill, and around window openings? I understand the idea of a raised footer, but it seems like the stucco/plaster has to extend to the slab surface, forming a capillary wick (?).


15.
Aug 6, 2011 12:18 PM ET

Response to Kendall Willets
by user-756436

Kenneth,
The reason that a Nebraska-style wall needs to be pre-compressed is that if a newly-laid wall is plastered immediately, the settling (which is driven by the weight of the upper courses of bales plus the roof load) will pull the plaster down with it and cause the plaster to crack. After all, the plaster is intimately bonded to the straw bales.

The plaster is an important structural component of a finished wall, if it is installed after compression. However, if you plaster too early, the thin plaster is not able to resist the forces generated by settlement, and the plaster cracks.

Concerning your other questions: I invite GBA readers who are experienced at straw-bale construction to reply.


16.
Aug 8, 2011 9:59 PM ET

Straw bale housing
by smalld

When you include rammed earth as an unlikely alternative to strawbale, you may not be aware of a design system called Sire-Wall; which is a system incorporating insulation within the the envelope of rammed earth. The system is, albeit quite costly, a very energy-efficient and long lasting alternative to strawbale construction. Check them out.

regards-
smalld


17.
Aug 9, 2011 9:19 AM ET

SIREWALL also claims their
by user-945928

SIREWALL also claims their walls are the 'performance equivalent' of an R-50 wood-framed wall...


18.
Aug 9, 2011 9:30 AM ET

More on Sirewall
by user-756436

Mike,
Thanks for the warning about performance exaggerations. The Sirewall system appears to use 4 inches of "rigid insulation." I can't find anywhere on the company's website where the insulation product is described (that's a danger sign right there). But if it's XPS, that would be about R-20 insulation -- plus some dirt on either side.


19.
Jan 22, 2017 1:24 AM ET

Good article
by joem789

I think straw bales are a great option. But the plaster part is completely unnecessary. The only reason it was invented was out of necessity. Think about this. Any insulation you put into a wall is going to need to stay dry. If it doesn't, the wall will have to be opened up and fixed. So no matter what you use, it is assumed that you are going to know how to make a cavity air tight, waterproof, and keep out critters. SO it doesn't matter what you put in there as long as it has a good R value. Too much fear mongering going on. People are too worried and rely on "expert" advice too much. Use your own mind people. They tell you not to use grass. BUT YOU CAN. It isnt going to rot because it will be dry. And its easier to make then straw bales. But the experts wont tell you that because they cant make any money off it.


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