"STRAWBLOCKS"
A BIT BEYOND YOUR AVERAGE "FIELD-BALE"
by Don Stephens - USA
It all began with a call from Jim Armstrong, a visionary representative of our local Spokane County Conservation District. From working together on past environmental education projects, he knew I was always on the lookout for new, eco-friendly building materials and that I'd been designing with strawbale for a number of years.
He announced "I've got a very different kind of bale down here, that I think you're going to want to see." He also indicated he sought my take on whether it might have rather revolutionary potential for eco-building applications.
My curiosity was obviously peaked, so it wasn't long before we were standing over the subject of his enticement. It LOOKED a bit like the bales I'd been around since childhood on the farm - obviously made of straw and bound together with twine, but it also had some obvious differences.... First, it was tied every three inches up the sides, with the straws vertical. Second, the upper face was so much more dense and smooth, almost like a block of wood. And the size seemed odd. So I said "OK, Jim, I'll bite, tell me all about it.
"Well, first of all," he replied, "it's really only half a bale and what you're looking down at is where it's been sawed in two, across the straws ,by a chainsaw, between ties." While he spoke, I was trying to push my thumb down into the cut surface, without making any real dent. Impressive!
He went on to explain that it was cut from what was actually a "re-manufactured" bale, punched out by a huge stationary press originally designed to squeeze hay-bales into minimum volume for shipment overseas. These would go by container vessels, mainly across the Pacific rim. Since the charge for such transport is by volume, the more tons that could be condensed to fit in each container, the less it costs to ship.
(The initial reason our Conservation District investigated this system had to do with "the blue-grass problem." In the last half century, eastern Washington and northern Idaho have become major growing areas for grass for lawn seed. It's a perennial, so you plant it and it grows and puts up seed heads, which are harvested as a cash crop. And then, traditionally, you set the field afire to burn off the straw and stimulate next year's seed growth and another lucrative harvest.
But, the smoke has now been linked not only to general air pollution and smog but also to serious and sometimes fatal reactions in those with allergies and asthma, and its fine particulates have been shown to contribute to worsening a host of other health conditions as well. So law suits were filed and political pressure brought to bear. In Washington State, the Department of Ecology passed a rule phasing out grass-burning over a three year period and it was up to the conservation districts to provide farmers with viable alternatives. Idaho hasn't established a ban yet, but the issue IS in the courts and "the handwriting is on the wall." And similar restriction of wheat-straw burning is evolving in both states.)
At first, farmers were just baling the straw and piling the bales up along the field edges by the thousands to rot, making way for next year's growth. And in more than one case they put out the word that it was free for taking, with bale builders responding enthusiastically to the call.
But a number of other answers are being explored...making it into paper or strawboard, using it for bio-fuel, composting it for methane production, and using it for feed supplement. It's to take advantage of this latter market, particularly in Japan, that compressed re-baling offers potential. But Jim also had another idea...using these "super-bales" for building. And after examining one, and hearing a bit more about them, I tended to agree.
I was curious about sizes and how they were produced. He explained that some are made from regular three-string bales. In the Steffen Systems press used for the sample we were examining, these are loaded, on edge, onto an intake "table" at the front end of a machine about 25 feet long. As they cue into the throat of this massive white compressor, the strings are cut and they are drawn forward, one behind another, till enough fiber is inside to make one compressed bale.
Just how much that takes varies somewhat, depending on initial and intended final density, but usually about a bale and a half is sufficient. This 5' to 6' of straw is subjected, through a moving plate, to a million pounds of pressure from massive hydraulic pumps, condensing it down to about 11". Then cords are automatically tied around and it's allowed to expand back out to almost two feet (meaning it's still over half air, but only takes up about one-third the volume it had as originally field baled.)
The finished product feeds out, measuring 16" wide, about two feet high (with the straws vertical) by two feet long, weighing nearly 100 pounds, and bound by six ties, the first one 4" up from the bottom. Another even larger unit from the same company can split a 3' x 3' x 6' or 3' x 4' x 6' "giant" field bale, as nice as you please, into condensed versions still with the same width and length dimensions as from the smaller press, but about 34" high, with more ties and commensurately heavier.
I had questions. Did it matter what kind of straw was used? He said no. What happens when you cut the strings...does it explode? No, again. It seems that after it's been tied a half hour or so, it takes "a set", and if undone, just plops apart like the books in a regular bale. What about R-value and bearing strength?
My clear answer to the latter came a few weeks later, thanks to Steve Burchett of Budinger & Associates Geotechnical & Materials Engineers. They have a big calibrated testing press and put several sample bales (both grass and wheat straw, from the two different re-compactors) under load. And the result - deformation began at 2,500 psf, meaning a wall bearing capacity of over 3,000 pounds per linear foot. That gives a whole other meaning to the term "load-bearing"!
The R-value answer proved more elusive. I checked into testing options and found two...one company could test a small sample in the device they use for space shuttle tiles; very accurate, but how do you neatly cut and contain a chunk 4" square and 1 or 2 inches thick out of a high-density bale, to fit their precision machine? The other company wanted a stuccoed 10' by 10' wall section delivered to their facility 350 miles away...also a bit challenging!
I understand that one try at the latter type test WAS made by volunteers working with the SCCD, but (according to a participant) "with poorly made bales, poorly stacked and still damp from stuccoing" and came out around R-23. I tend to suspect a fairer figure for a well-made, dry wall would be more like R-28 to 30. I base this on the fact that we know the bale is still about half air (inside off and between more, but further-compressed, straws-per-inch than a field bale) and with the relevant "R" measured cross-ways of the straw's "grain".
More basic, "hands-on" tests suggested to me these bales had some other things going for them: A drywall screw inserted 2" felt very solid and could only be pulled out with pliers and major force. "Robert pins" had to be pounded in with a hammer. The faces were far smoother for stuccoing.
And the ultimate test-for-contractors was: when you kicked one hard with
your steel-toed boot it really hurt, like you're hitting a block of
wood...not some wimpy, mushy "farm product". This was a real, macho,
BUILDING material!
But the real test of the pudding IS in the tasting, so I was eager to build with these "straw-blocks". And the opportunity proved to be at hand. A couple had recently written me that they'd saved a flier from one of my home-show displays years earlier, touting the merits of earth-sheltering (what's now more fashionably called "living roofs" and wall berming), and now they were ready to build that way, southwest style, on their rural site.
For such a location, with wheat fields all around, I broached the idea of building with straw-bale in exposed wall areas and in the roof, and although they hadn't been thinking that way initially, the idea appealed to them. It also became evident that for their design, even with its high roof-load and partial second story, load-bearing was a possibility, if the recompressed bales were used. I cautioned them that so far as I knew, this would be the world's first experimental application of such a technology, and that "pioneering" opportunity appealed to them too.
So we proceeded with the design of their Moran Vista "hacienda". The under-lying structure supporting longer spans between the loadbearing walls and underpinning the second story floor system would be of salvaged, fire-killed logs "in-the-round", the roof would be 14" field bales as insulation and blocking between 18" composite wood "I"s (TJIs) and we would use my "vertical crawlspace" technique under the north and west berms to maximize storage and reduce wall loads and concrete. The second-story sub-floor, exposed as ceiling in dining and kitchen, would be of peelers (see TLS #41, p. 12) as would the eave overhangs, a natural latilla look to carry out the "Spanish" theme.
For primary heat we would capture the solar-heated air from the peak of the second story's tile-configured metal roof in summer and run it down through under-slab tubes in such a way as to time-lag its return for counteracting winter heat losses. This would make the solar heat build-up typical of metal roofs an asset, while drawing it away before it could force its way through the bale insulation...thus assuring a cooler home in summer.(See more on this "annualized geo-solar" path in TLS #38, p. 19.)
An indoor 7' x 14' "swim-against-the-current" Endless Pool, which the clients had already purchased, was to be installed in the rec room. And so, for bare-foot comfort, we specified in-floor hydronic water tubes. I originally hoped to recover part of the annualized geo-solar warmth rising into the crawlspaces with Heat-Pump-Water-Heaters to furnish both hydronic and domestic water. These units could also have been ducted to extract heat from in-house air in summer, converting it into hot water for taps and pool and offering optional air conditioning. But unfortunately, there was an "availability-gap" at just that time, when DEC no longer made HPWHs and ECR (see TLS #41, p. 30) hadn't yet begun. So we ended up going with a propane back-up, something we'd all hoped to avoid for eco-reasons.
Getting back to the actual use of the high-density bales, several issues arose. The first was availability. When first chosen for use in this project, we thought they would be furnished promotionally by a new local press, but that unit failed to materialize. So we had to look to other options. One was to go back to non-loadbearing infill field bales and an all-log post and beam frame, to support the non-typically-high "living-roof" and multi-story loads. But some quick calculation showed that, factoring in savings with field bales against higher costs for posts and their footings, this would add nearly $10,000 to a project of this size.
The other possibility was other high-density presses. By checking with David Steffen, I located one in northeastern Oregon and another near Moses Lake, Washington. I was able to arrange with a straw broker, just a couple of miles from the latter to deliver straw to them, have it recompressed, loaded in two 18-wheeler trailers and delivered to the job. The trailer supplier let us rent those units at a modest price per month to stay at the site to protect the bales until installed and provide a much-needed winter wind-break to the southwest of the constuction as well.
The second issue was just how to build with this different breed of bale. One glance at the density of these "blocks" made clear one was not going to internally pin the walls by easily slipping bamboos down through them!
So external options were up for consideration. I'd seen and played with tied-through surface pinning techniques with bamboo and reed at the International Strawbale Conference at Blackrange a couple of years earlier. And Habib (Gonzalez, building up in B.C. Canada) had shared with me how he was working with techniques using heavier metal mesh in lieu of poultry wire, as a labor saver.
Also, I'd been called in as a consultant to the local building department regarding a "bandit" bale builder, who'd been "caught in the act" bale-upping an un-permitted stable and hay-shed, been "red-tagged" and then gone ahead, in spite of the stop-order, and stuccoed the bales. They wanted me to go out and do an evaluation for them...structural soundness, bale moisture level, etc...and make a recommendation on whether the result was safe enough to allow. (I was impressed with their amenability...SOME building departments would have merely taken such a "cowboy" approach as a personal challenge to their authority and summarily ordered it torn down..AND maybe, imposed a stiff fine too!)
As it turned out, soundness wasn't really in question. He'd already built his wood structural frame on concrete post footings and had it approved... he just "neglected to mention" he'd be closing it in with bales. Then he'd poured an outboard independent running footing for his bales. He applied 9 gage "horse-wire" mesh to the outside face of the posts, shoved the bales up against the outside of the mesh, put 14 gage wire outside that, tied the "in" and "out" mesh together with baling wire and shot it with stucco. It seemed to work great as surface pinning and produced a very "true" wall.
So, drawing on this background, I decided to have the bales placed in STACKED bond (being only 2' long, RUNNING bond would not give nearly as much direct load transfer downward, if a good part of each was hanging over the curved faces forming joint between the two below.)
I called for 4' x 7' flat mats of 6x6/10-10 welded-wire slab mesh (that's ten gage wire forming 6"x 6" squares) placed on each wall face, pinned to each bale at four places (each side) with "Robert Pins". These were to be pounded in at a diagonal over mesh intersections, with a 3" long piece of 3/8" bamboo at the opposite diagonal slipped behind to hold the mesh out away from the bale face (please see the isometric illustration). This would assure that the mesh was more centered in the stucco where it would perform best structurally.
I also called for tie-through from one side's mesh to the other at 2' centers, both ways, to prevent the possibility of stucco separation from the surface of the bale in the event of a severe earthquake force perpendicular to the wall axis. This was easily accomplished by just laying doubled bailing wire on top of each bale's middle, before placing the next layer and then tying to the mesh later, as it was placed and pinned. And in those cases where one was missed or fell out, it also proved easy to "sew" them through later in the horizontal joints.
The high-density bale surfaces with this secured mesh system took the stucco well and, though there were some "echo" hair-lines over the mesh grid in the scratch coat, the integral-color finish surface was as crack-free as any. (For this finish we used white "Portland" mixed with sandy earth, with warm and even results.)
Complicated as this pinning technique may seem to describe, it proved to go very quickly in practice and produce a very stable, flat wall. When the heavy tamarack load-distribution logs were lowered on top of these still unstuccoed walls and cross-logs bolted or pinned to them, they neither budged nor measurably settled.
A third question was how it would be to work with these "straw-blocks"? They were great. Height adjustments were so easy with a chain saw...since there was 4" of "meat" at the top and bottom of each bale, outside the strings, and since one could cut between any two strings as well, tuning wall heights was a breeze. Re-tying proved easy and soon the guys where making "L"-shaped bales for around window openings, cutting in pipe chases behind the strings and such, all with ease on the first try.
A fourth concern in my mind was what the moisture intake and release charactoristics would be, compared with field bales. I knew from previous monitoring that a 10% moisture field-bale wall would jump to about 25% almost immediately after stuccoing, but drop back down to 10% in three to four days in our climate. I hoped the high-density "blocks" would behave similarly - they seemed to in pre-testing, but there's always that little nagging concern that real-world peformance may somehow prove different.
So three days after scratch-coat I was out there prodding the bales and pleased to see them back at 10%. They not only seem more resistant to water penetration, but give it up easily. And even bales left unprotected through a heavy rain (as an intentional test), straw-ends up, seem to dry quickly, none the worse for wear structurally.
The other question was cost. Including about 100 miles transportation, they only ran about a third more per square foot of wall surface than regular bales, so where their special charateristics are of benefit, I wouldn't hesitate to use them again. (One could check with Steffen Systems or other manufacturers to see where or whether their units are in operation near you. I note on my several-year-old list from David Steffen, for example, that his units are in most western states plus Pennsylvania, Saskatoon,SK and Winnipeg, MB in Canada, and Melborne, Australia.)
Are they THE answer for every project? I'd say no, and will continue to use field-bales where they're up to the job. But on designs suggesting load-bearing walls, when I want to support heavier roof-loads, longer spans or multiple stories, or when circumstances make on-site mechanical wall compression difficult, they certainly offer some major advantages. And the ease of screwing attachment plates, nailer strips, electrical boxes and such directly to them is another added plus. (Or for a deeper electrical box "set", one can cut a neat circle between strings with a hole saw and pound in one of the molded round boxes with the self-securing ridges.)
I expect to use them again, often. In fact, they're an important part of the mix on three of my current projects. One small home just now starting construction will sit on a raised, earth-filled, annualized-heat-storing rastra plinth, used to "level-off" a steeply sloping site for a client with mobility limitations. On the drop-off side, the load-bearing bale wall starts on the cantilevered slab-edge nearly 10' above grade, so hanging out-board, applying some mechanical pre-compression technique to field bales would be tricky. There will be no such pre-stuccoing settlement to address with high-density bales.
On the other two, a combination of earthed roofs and load-bearing multi-story elements are facilitated by these straw blocks, as they were in the Moran Vista prototype described above. And on one of these, the "story-book"-style home/earth-sheltered community-building "duplex" portrayed in an accompanying sketch, the fact that we can drywall-screw applied trim and "coins" of rastra-panel directly to the bale-wall surfaces to give three dimensional reveal to the stucco will help economically facilitate the client-desired design theme.
What could be done to further improve these higher-tech bales? David Steffen and I discussed this briefly a while back. (He seemed most enthusiastic about seeing them used for construction and willing to explore ways to modify his machines to do the job better, when demand justified it.) I said I'd like to see bale ends a little more square (flat), leaving less gap at vertical joints. And for our "non-metric" market, I indicated a more precise 2' by 2' module would be handy.
He thought those were both fairly easy possiblities. And he also suggested that the press-box might fairly easily be modified to make "tongue" ridges in the bale-tops and groves on their bottoms to make them interlocking (!) and to accomodate wiring runs.
Also it would be nice to see them pre-made and sitting in inventory at our local lumber yards, just waiting for instant pick-up, like so many other building products...but that will come, if they catch on with main-stream contractors as they very well may, in time. After all, it's hard not to like a construction material so solid that kicking it could break your toe!
DON STEPHENS was trained in architecture at the University of Idaho and has been pioneering alternative building since 1960. His current projects incorporate the above-mentioned materials and techniques as well as a host of others including earthbag foundations, tirebales and solar closets. He may be contacted at dsteph@sisna.com or (509)838-8222
References:
Steve Burchett, BUDINGER & ASSOCIATES, INC. geotechnical and materials engineers
3820 E. Broadway
Spokane WA 99202
(509) 535-884
David Steffen
STEFFEN SYSTEMS hay handleing equipment
2882 Howell Road NE
Salem OR 97305
(888)783-3336
Email: hayman@steffensystems.com
Website: www.steffensystems.com |