Straw bale in Eastern Oklahoma? Hot and wet.......

Hey Everyone,

I have finally made the move to 40 acres in Eastern Oklahoma.

I had been considering straw bale construction for years but have a concern that the climate here may not be conducive. 40 inches of rain/year.

The rain can be pretty extreme and I know that moisture is a concern with straw bale.  

I can extend eves and gutters out 2'-3' from the walls but wind driven rain will still hit the walls.

What do you all think of building with straw bale in this climate?


Thanks

Stephen

40 inches of rain will not be an issue.
Good design of the structure and its exposure to driven rain will deal with that.
Lime plasters on the outside are important.
From; https://strawbale.com/protecting-straw-bale-home-weather/
"rain. This is perhaps the easiest form of water to deal with in a straw bale home.
Large overhangs, preferably 2′ or more, will direct the majority of the rain away from the walls by protecting them from direct contact.
With the application of gutters on the eaves, you can virtually eliminate rain from contacting the walls.
The gutters also give you the opportunity to collect your rain water for future use. [ see my signature for rainfall collection ]
If you have a multiple story building, be sure to add roof lines at each story. "
From ; https://www.thelaststraw.org/moisture-and-straw-bale-walls/
"Liquid Moisture
Primary consideration needs to be given to preventing liquid moisture from finding a way into the bales:
-ensure appropriate overhangs, splash protection, window and door detailing, etc.,
- and don’t forget to remember adequate protection for the bales during the actual construction process.
- Taking care in detailing window and door openings by design and implementation is very important
—providing a drip edge at the tops and bottoms of the openings, making sure that any “ledges” (such as at the bottom of a window opening) are sloped appropriately, and installing a sheet-type Moisture
   Barrier such as tar paper, or felt, over areas above, beside, and below openings in the wall system before stuccoing
   in consideration of any potential water intrusion that might occur at junctions of dissimilar materials.
- Some straw-bale builders in wetter climates feel that tar,paper isn’t sufficient, that it’s too easily punctured by the building elements (or builders)
—in which condition the tar,paper can potentially create a bigger problem than it solves—and recommend more flexible and self-healing membranes such as Bituthene or Ice & Water Shield (which is not intended to be an endorsement for WR Grace, which happens to be the manufacturer of both of those products).

It should be pointed out here that there is a profound difference between vertical water and horizontal water where straw bales are concerned.
Vertical water—such as driving rain hitting the sides of a straw-bale wall—is shown by experience to not penetrate very far.
Horizontal water, on the other hand, will seep from above into the middle of the bale wall, which is precisely the worst place for it to be."

Drip ledges should stand proud of any plaster to ensure water does not dribble down the plaster causing erosion.
A wider veranda with an extra shield can be installed where the rain is particularly fierce.
Good luck with it.

John C Daley wrote:40 inches of rain will not be an issue.
Good design of the structure and its exposure to driven rain will deal with that.
Lime plasters on the outside are important.
From; https://strawbale.com/protecting-straw-bale-home-weather/
"rain. This is perhaps the easiest form of water to deal with in a straw bale home.
Large overhangs, preferably 2′ or more, will direct the majority of the rain away from the walls by protecting them from direct contact.
With the application of gutters on the eaves, you can virtually eliminate rain from contacting the walls.
The gutters also give you the opportunity to collect your rain water for future use. [ see my signature for rainfall collection ]
If you have a multiple story building, be sure to add roof lines at each story. "
From ; https://www.thelaststraw.org/moisture-and-straw-bale-walls/
"Liquid Moisture
Primary consideration needs to be given to preventing liquid moisture from finding a way into the bales:
-ensure appropriate overhangs, splash protection, window and door detailing, etc.,
- and don’t forget to remember adequate protection for the bales during the actual construction process.
- Taking care in detailing window and door openings by design and implementation is very important
—providing a drip edge at the tops and bottoms of the openings, making sure that any “ledges” (such as at the bottom of a window opening) are sloped appropriately, and installing a sheet-type Moisture
   Barrier such as tar paper, or felt, over areas above, beside, and below openings in the wall system before stuccoing
   in consideration of any potential water intrusion that might occur at junctions of dissimilar materials.
- Some straw-bale builders in wetter climates feel that tar,paper isn’t sufficient, that it’s too easily punctured by the building elements (or builders)
—in which condition the tar,paper can potentially create a bigger problem than it solves—and recommend more flexible and self-healing membranes such as Bituthene or Ice & Water Shield (which is not intended to be an endorsement for WR Grace, which happens to be the manufacturer of both of those products).

It should be pointed out here that there is a profound difference between vertical water and horizontal water where straw bales are concerned.
Vertical water—such as driving rain hitting the sides of a straw-bale wall—is shown by experience to not penetrate very far.
Horizontal water, on the other hand, will seep from above into the middle of the bale wall, which is precisely the worst place for it to be."

Drip ledges should stand proud of any plaster to ensure water does not dribble down the plaster causing erosion.
A wider veranda with an extra shield can be installed where the rain is particularly fierce.
Good luck with it.

John,

Thank you for the fantastic reply!! So much good info!

I would be building the structure and roof first then infill with bales. I should be able stack/store the bales under the roof upon delivery.  That should address moisture concerns during construction.

Good tips on the window details and ice & water shield.

Rainwater collection is in the plan. I wish I could find affordable tanks....... They are bringing $1 a gallon or more here.  IBC totes may be my only option. Unfortunately 20+ IBCs and plumbing is an eyesore.......

Lime plaster is also in the plan.

Looking at my draft design, I do still have spots at the corners of the gable walls that may need to be addressed.  Let me see if I can post a picture,

Thanks.

Stephen

By the time people fiddle around with 20 IBC and fittings, you could have bought a single 20,000L tank installed.

Hi Stephen,

You might pick up a copy of Straw Bale Building Details: An Illustrated Guide for Design and Construction by the California Straw Building Association.  It’s a relatively current (2019) resource for best practices in straw bale construction in North America. Lots of discussion, pictures and drawings that illustrate much of the advice John offered.  The IRC’s Appendix S Straw Bale Construction, the building code applicable to those code jurisdictions that adopt it, is referenced throughout and printed in the book.  I don’t think Oklahoma has adopted this code, but you can lean on it if your building code jurisdiction has an alternative materials and methods provision.

You can definitely build a structure with straw bale walls in your part of the United States—there are straw bale buildings in nearly every U.S. state, every Canadian province, throughout much of Mexico, and in over fifty other countries.  As John said, 40” of rain isn’t a problem so long as it doesn’t wet the walls.  If you get a lot of wind-blown rain (see below for more on this) you might extend your roofline beyond 2’.  I have worked on many projects where the straw bale wall height and prevailing weather required 3’ and 4’ overhangs, and even 8’ deep porches to protect the most weathered walls while also providing functional outdoor space.  

My experience as a builder specializing in new straw bale construction and repairing/remodeling older straw bale buildings leads me to be cautious about relying on plasters for protection against wind-driven rain, unless it’s minimal, infrequent, and followed by periods of sunny, dry weather.  

We ask a lot from exterior lime plasters in a straw bale wall assembly. They need to be vapor permeable so any moisture that gets inside the wall can escape.  They need to be durable and resist insect and rodent intrusion.  Sometimes they play a structural role in resisting in-plane or out-of-plane forces.  And of course, we want them to be low maintenance and beautiful!  

Exterior lime plasters applied directly to straw bales are a “reservoir cladding” siding system.  It doesn’t matter if the lime is Type-S, Naturally Hydraulic Lime, quicklime, or some code-approved combination of Portland cement and lime—they all have trade-offs, but once on the wall they perform similarly.  Reservoir cladding systems absorb liquid water from wind driven or splashing rain (though some water may also run off).  That liquid water soaks some distance into the 1” + thick plaster.  The moisture evaporates back out when sunny, dry conditions return.  The reservoir fills and empties, fill and empties.  

This works really well in places where rainfall typically doesn’t come down sideways, or if it does, only for brief periods.  For example, here in S. Oregon my very exposed hillside home site receives wind-driven rain for a few minutes ahead of some storms, followed by a week or two of sunny, dry weather.  This cycle repeats from November through April.  John describes it well: “vertical water—such as driving rain hitting the sides of a straw-bale wall—is shown by experience to not penetrate very far.”  In my situation, water doesn’t penetrate far into the plaster—perhaps ½”.

This understanding of how well plasters protect the bales is so widely accepted as to be a “received wisdom” handed down for decades.  Unfortunately, reservoir siding systems don’t work so well in places that see wind-driven rain hour-after-hour, day-after-day, with little dry-time opportunity between rain events. Think coastal Oregon, which can receive 60” to 80” of rain a year, some of it coming down near-horizontally for days-on-end followed by a week of damp, overcast weather...and then more rain!  Or portions of the Eastern and Southern U.S. that experience hurricanes.

How far wind-driven rain penetrates into the 1” or so of exterior lime plaster depends entirely on the amount of water driven into the wall and the amount of dry-out time between sideways rain events.  Sadly, I have removed plasters from straw bale walls that received too much wind-driven rain and found that the straw in contact with the plaster had largely decomposed.  

Lime plasters are not water-proof.  They are actually quite absorbent, and enough water soaking into the plaster from wind-driven rain (or ground splash) can overwhelm the “reservoir capacity” and pass that water into the adjacent straw bale.  

And that’s a problem.  Once saturated, lime plasters allow liquid water to readily pass through them, but water in vapor form escapes much more slowly.  Under favorable drying conditions this could take weeks, and even months!
 
Any time the moisture content of the bales exceeds 20% you’re heading into the danger zone.  As the moisture level climbs higher dormant microbes naturally found on the straw become active.  If the right temperature conditions are present (above 50 degrees Fahrenheit) and the moisture level remains high the decomposition process begins, and ends only when moisture conditions drop below 20% or temperatures drop below 50 degrees.  This is a problem for any cellulose-based building material, but because straw has much more surface area (compared to wood) the potential for damage is greater.

If really big roof overhangs aren’t an option for you, there’s an alternative that still uses straw bales.  Over the past few years I worked on a number of straw bale buildings that used plywood for shear walls.  They were framed with 2 x 4 studs on 16” or 24” centers, then sheathed with 3/8” or ½” plywood (not OSB!).  Plywood is on the very edge of being just vapor permeable enough for a straw bale wall assembly in our area—a temperate climate characterized by warm, dry summers and cool, wet winters.  I’m not sure how it would perform in climates characterized by warm, humid summers or extremely cold winters...it may be as simple as drilling small holes (to increase vapor permeance) in some or all of the plywood sheathing if it doesn’t compromising structural integrity.

Here in the Western U.S. a 2-string bale is around 16” tall (18” wide, approx. 39” long), and a 3-string bale is around 23” wide (15” tall approx. 48” long).  We stack the bales on-end between the 2x studs.  A 2-string bale gives us an 18" thick straw bale wall (without plywood or plaster) and a 3-sting bale gives us a 15" thick straw bale wall (again, without the plywood or plaster).  The 2-string bales need to have one edge notched to fit around a 2x, and the 3-string bales need some stuffing to fill the 1" wide vertical gap.  Both walls have an insulation value of around R-28.  There are a couple of ways to keep the bales secured to the studs—we use long screws and 6 x 6 plywood washers on 2’ vertical centers, though others have used baling twine.  None of this is prescribed in Appendix S Straw Bale Construction, but it’s something engineers familiar with straw bale building have come across, and it’s described briefly in CASBA’s book.

Plywood sheathing is among the most common lateral force resistance systems in North American residential construction so most builders and building code officials are familiar with it.  Since straw bale walls are much heavier than conventional insulations, these walls need serious hold-downs embedded in the foundation wall, and the nailing schedule may be different from conventional, but now you have exterior finish options.  You could apply lime plaster just as any lime plaster might go over sheathing—2-ply building paper, mesh, three-coat lime plaster regime.  Or, you could install any kind of siding you like over the sheathing—metal, cement board, wood.  If you’re really concerned about wind-driven rain you could also add a rain screen to either the plastered or sided exterior walls.  You still need to be careful about flashing windows, and I recommend sills to direct water running down windows  away from the wall, but this wall assembly is a huge improvement over reservoir cladding systems where wind-driven rain is a concern.

On these projects we usually apply clay-plasters to the interior surface of the straw bale wall.  We apply interior lime plasters too, but clay plasters are more forgiving, easier to repair, are better able to moderate interior humidity, and more.  We also do a really good job of air-sealing the interior walls.  Not much vapor is going to pass through the clay plaster itself, but as with any building, most water vapor that gets into the wall hitched a ride on air moving freely through gaps and cracks where the walls meet windows, doors, partition walls, ceilings, and all the tiny holes in electrical outlet boxes.  Prevent air movement into the walls and you’ll also block the primary route moisture takes to get there.  

I also agree with John about the rainwater collection system.  Much easier in the long run to use one or more large tanks than fuss with connecting dozens of smaller tanks.  Here, the “sweet spot” in terms of cost/gallon is an above-ground 2,500 gallon poly tank that is about 8’ tall and 8’ diameter.  There are trade-offs of course.  Some consider above-ground poly tanks an eyesore, and they'll degrade if not shielded from the sun.  Below-ground tanks solve this problem (and keep your water cool!), but cost more and the connections are more difficult to access for repairs and maintenance.  Above-ground steel tanks are popular and readily available in your area, but their longevity comes with a higher price.

Jim Reiland
Many Hands Builders

Hi Stephen,

I should have mentioned that you can also apply siding over a plastered straw bale wall so long as you have planned ahead for a method to attach the siding--screws and nails won't hold siding if driven into just plaster and straw.  To reduce the buckling associated with lateral forces like wind and sagging from the pull of gravity most siding manufacturers recommend attachment at 24” centers or less.  

We’ve installed both vertical and horizontal siding over plastered straw bale walls.  You still want to plaster the walls--it functions as an air barrier and the back-up moisture barrier.  And of course, it helps keep the wall's fire rating at 1 hour for earth plasters and 2 hours for lime or cement-lime plasters.

Horizontal siding. Apply horizontal 2x ledgers in the bale wall, make careful notes about their height before covering the wood with strips of building paper and lath/mesh and applying a scratch and brown coat. Try to keep the plaster surface as flat and plumb as possible, otherwise bulges in the bale wall will appear as bulges in the siding.  We then added 1x horizontal furring strips and some type of strip screen (like Cor-A-Vent) at the top and bottom of the wall to keep insects and rodents out, and allow for air movement and water drainage.  Then we installed horizontal wood or cement board siding.  

Vertical siding. Use the 2x or 4x vertical framing you might already have in a non-load-bearing wall design, supplemented by additional 2x vertical framing let into the wall if the spans exceed a few feet. As with the method described above, cover the framing with strips of 2-ply building paper, lath/mesh, and apply a scratch and brown coat. Keep note of where the vertical framing is located, and affix horizontal furring strips on 2’ centers.  These furring strips could block air movement and drainage unless they have  holes or notches in them.  We've worked on projects that used vertical metal siding and shou sugi ban siding.

Note that with either of these methods you’ll still need  something to resist lateral forces.  The CASBA book I mentioned in my earlier post describes a dozen different ways to supply lateral force resistance in a straw bale wall assembly.  If you don’t need to worry about earthquakes you may be able to use steel strap tension-only bracing (often called metal “x” bracing).  Other options include a straw bale shear wall (relies on a carefully detailed plastered straw bale wall), prefabricated wood or metal braced frames, and more.  

Jim Reiland
Many Hands Builders

Jim, thank you for the explanation about the "“reservoir capacity”  of external plasters I have never heard of that description before.
Jumping to the end, where you discuss the longevity of plastic tanks and the appearance of them.
In Australia, I have tanks that are 35 years old and have no sign of degradation.
As for appearance, I see them as symbols of self sufficiency and I dont see them in a negative way.

Hi John,

I think the only other reservoir cladding system in common use may be brick walls?  There was a wall system I saw in California--not sure if it's still allowed--that applied mesh and stucco against building paper that was held in plane against tightly stretched wires--no sheathing.  Insulation filled the cavity directly against the backside of the building paper.  Not sure if the paper separation would make it any less a reservoir system.

I agree about the aesthetics of plastic tanks.  I don't mind them, but have designed plenty of projects where clients wanted them out-of-sight.  As for durability, some time ago I saw a manufacturer claim that poly tanks have a service life of around 25 years. Since exposure to the elements is really the only way the tanks could degrade, I'm exploring ways to plaster them over with stucco, which would also offer some protection from burning or melting in a wild fire. One of my crew is wildlands fire fighter; said he has seen plenty of plastic water tanks burned/melted down to the water line.  

Jim Reiland
Many Hands Builders

I am with you on the burnt tanks, I am not sure if any protection can be created for them.
Yesterday I met a bloke who explained the reason brick houses explode sometimes in fires and wearthborad homes dont is as follows;
- fire front has temperatures of about 5000 deg. C
- air behind the brick is superheated very quickly
- it expands rapidly causing an explosive effect.
Weather board homes have the same issue, but the boards just pop open and the explosive force is dissapated,

Have you heard that evidence?

Hi John, I know this is drifting off topic for Stephen's question about building with straw bales in Eastern Oklahoma, but I haven't seen exploded brick walls.  I don't doubt it though.  I have seen plenty of other damage to masonry in the aftermath of a fire.  I lived in Oakland, CA at the time of the 1991 Oakland Fire, and I live near the 2020 Almeda fire in S. Oregon.  If it gets hot enough, fire can destroy CMU walls, brick walls, concrete walls.

Back to plastic tanks.  If I place plastic water tanks covered with 1" of plaster in the middle of a patch of dry brush and dry woods, or adjacent to a wood shed  stocked with four cords of firewood--the plaster probably won't offer much protection.  Radiant heat is probably going to melt the plastic right through the plaster.  But if I locate the plastered tanks in the same way I would a house in the WUI--with plenty of defensible space around them out to 50' - 100'--I'm optimistic they'll survive.

We might want to start another thread on this topic--"fire resistant features for homes built with mostly natural materials."

Plastered straw bale wall assemblies have a pretty good fire rating, but most fires that threaten a home don't burn through the walls first.  By the time a wild fire has burned through a wall it will have already come through windows, doors, attic and crawlspace vents, all of which can be hardened or prepped to better resist or exclude fire.  Just about every straw bale building I worked on during my career was in the WUI (Wild-Urban Lands Interface), and most of these structures were designed with wildfire in mind.  If they weren't I recommended or added those features.

Jim Reiland
Many Hands Builders

Thank you ALL for the replies!!

I am overwhelmed with good information. It is going to take me a bit to digest it all.  Thank you for such thoughtful and detailed repleis.

I do have a couple of random questions right off:

- Is there a practical limit to the thickness of the lime plaster on the outside wall?

- I am looking at two possibilities for protecting the lower portion of the exterior walls. either a stacked stone wall 42" tall in front of the bales with a small air gap and lime plaster on the bales. Kind of a "wainscot"  look. Or, building the first 42" of wall from rammed earth as a "base" for the bales. Do you see any issue with either of these?

- Regarding rainwater collection: Connecting a bunch of IBC's together to make an adequate storage tank is a PITA. I have done it. BUT... In my area used (not IBC) tanks bring around $1 a gallon. IBC totes are closer to $0.23 a gallon plus plumbing to connect them. Even with the plumbing, IBC's cost 1/3 what regular tanks do. As an alternative, I am considering an above ground swimming pool with a cover on it as a storage tank.  Any thoughts? Has anyone seen a swimming pool used for this before?

Thanks again!!

S.
 

Hi Steve,

RE plaster thickness. I’ll go right to Appendix S Strawbale Construction, the applicable building code with commentary.  The principal authors of this code—Martin Hammer, David Eisenberg, and Mark Aschheim—said it best (I supplied the words between parenthesis for context):

“AS104.4 Plaster. Plaster applied to bales shall be any type described in this section (lime, cement-lime, clay, gypsum) as required or limited in this appendix (pertaining to straw bale structural walls).  Plaster thickness shall not exceed 2 inches (51mm).

(Commentary) ...The reason for limiting plaster thickness to 2” (51 mm) is that the additional weight of thicker plaster has potential structural consequences, especially in areas of high seismic risk.  Thicker plaster may also unacceptably reduce vapor permeability depending on the plaster used; however, there are also potential benefits of thicker plaster, including improved thermal performance in some climates due to increased mass.  The building official may allow plaster thicker than 2” (51 mm) if deemed to present no significant additional risk.”

When we talk about walls that “breath” we’re really talking about how well the wall allows water vapor to pass through it—it’s permeability.  Different materials allow water vapor to pass through them at different rates (or block transmission altogether), but this is affected by material thickness.  You’ll find different numbers, but cement plasters have so low a permeance (less than 3 US perms) as to be considered nearly vapor impermeable at 1” thick.  Mix some lime with the cement (20% lime, 80% cement) and permeance improves—and that’s what’s allowed in straw bale construction if you use a cement-lime plaster.  Lime plaster 1” thick has a permeance of 10 – 14 US perms, and clay plasters range from there up to 20 US perms.  Make any of these plasters thicker and their permeance drops.

There’s another practical reason for keeping the thickness under 2”.  The commentary above mentions weight, which is around 15 lbs. per square foot at 1” thick.  If the straw bale surface is the only lath for that weight, it’s probably OK, especially the surface of bales made with long straw fibers. (Bales made with flail chopped straw or straw that is partially shredded by a rotary combine harvester aren’t as good a lath as the much shorter fibers which can pull out.). The scratch coat takes a lot of effort because we’re pressing the plaster into the wall to make sure it keys with the bale surface.  But even with long-straw bales I have seen plenty of really thick plasters (e.g., 2" thick or 30 lbs./square foot) sag.  One option is to add a suitable mesh that supplies some additional lath--extra tooth for the plaster to hang on, and reinforces the plaster.    

RE protecting the lower portion of the straw bale walls with either veneer stone or building the wall above a rammed earth stem wall.  Question:  What are you protecting the walls from?  The building code and best practice is to elevate the straw bale walls at least 8” above grade.  I often start at 12”.  This addresses rain splash, but so does an extended eve (usually).  

If a veneer stone base, I think a rainscreen installation would be best—a ½” or so gap between the back of the stone veneer assembly and the plastered bale wall.  This gets complicated, but if you don’t do something like this, you could have moisture problems.  You used the term “dry stacked” but actually dry stacking veneer makes for a very unstable wall.  Steps:  Let a 2x6 ledger into the bales at the top of the stone façade, install drip flashing (Z flashing) to the upper portion of the 2x. This drip edge will probably be 3" deep--it will protrude beyond the finished plaster above it and cover the back portion of the veneer stone by at least an inch to keep any rainwater running down the plaster surface from getting behind the veneer and soaking into the bales. Then plaster above and below the drip flashing.  Next, attach 1x furring strips through the plaster into the ledger and the sill plate, cover that with ½ plywood to supply a firm backing for the stone, then 2 layers of building paper, a layer of expanded metal lath as tooth for the stone, and finally apply the veneer stone with a suitable mortar.  Remember, the Z flashing needs to cover the joint where this entire veneer assembly protrudes from the plastered straw bale wall.  It’s a lot of work, but looks really good!  Colleagues of mine have done this.  I worked on a project that was planning to but the client dropped this feature when they realized the extra effort and cost.

A rammed earth wall base for the bales.  I think that’s going to be a question for your engineer and the building department. I have seen straw bale walls stepped up on concrete stem walls, but not 42” high. I think the challenge will be anchoring the sill plates into the rammed earth wall.  All the permitted structures I worked on had sill plates secured to anchor bolts embedded in the concrete, bales on top of sill plates (the exception being straw bale walls over basements or crawlspaces where bale wall sill plates can secure to a sub-floor, but there’s still a sill plate under the rim joist that supports the subfloor, and that’s secured with anchor bolts into concrete).  I think that even rammed earth walls sit on concrete footings....

RE: IBC totes for water storage.  I haven’t seen IBC totes made with dark plastic to exclude light (and prevent algae growth), but you can paint or cover them.  

RE: swimming pools.  Lots of people in Hawaii use a covered swimming pool for water storage.

Jim Reiland
Many Hands Builders

Thank you Jim.

My reasoning behind taking extra steps to protect the lower portions is wind driven rain. Other structures at the building site tend to have wet exterior walls, up to about 36", when we have rain and moderate wind.  I am of a mind that if I run the eves out 3', with gutters, and protect the lower 42" of the exterior wall from direct moisture that I have a good chance at healthy walls.

Wind and rain have become significant concerns for me. When I moved here, I did not comprehend how much it rains. We beat Seattle by about 4 inches a year. And, it rains HARD.

I was not aware of a Straw code book with commentary. I need to get my hands on that.  

While I do have the flexibility of living in a place with no permitting or inspections, I really don't want to build a house that may fall on my head........

It will be some time before I start ordering straw but I have been poking around. I found a gent over in Arkansas that will sell me bales (2 string) @ $5.50 to my site. How does that compare to what you all have seen lately?

Thank you.

S.

Hi Steve,  

The International Residential Code's Appendix S Strawbale Construction is a model code available for any code jurisdiction (or builder!) to adopt or follow.  Lots of good guidance in them, and when paired with local best practice and common sense, can produce amazing, safe, long-lasting structures.

There's a copy of the code with commentary printed at the back of the book I mentioned, Straw Bale Building Details: An Illustrated Guider for Design and Constuction, available at the California Straw Building Association website https://www.strawbuilding.org/Straw-Bale-Building-Details.  You can also get it from internet and local book sellers.  I recommend the book--a good resource (and the most current treatment...2019) on this subject if you're just starting in on the design work.  There were twenty principal authors and another forty contributors--lots of experience and different points-of-view represented.  It's not a "how to" step-by-step recipe book about how to build a house with straw bale walls.  It's more like a cook book that explains how straw bales can be used to build a house, with lots of different methods described and illustrated.  They all work!  But some methods might work better than others in certain climates, or with some budgets, or for a builder's experience levels, so there's some discussion about tradeoffs with each.

CASBA also makes Appendix S Strawbale Construction available for a fee download https://www.strawbuilding.org/news/3587353.  It's free to you, but it actually costs CASBA something.  We pay the IRC for each copy that is downloaded, and I believe the amount we pay is just about what we earn from a book sale!

If I didn't say it earlier, CASBA is an all-volunteer, non-profit organization that advocates for the use of straw as a building material. All proceeds from book sales support research, development, education, and outreach efforts.  It's not just about straw bale.  You can also get a copy of the light-straw-clay code at our website, and soon I heard, a copy of the cob code.  All of these wall systems use straw to some degree.  If there's ever a straw-block or straw panel or straw cable or blown-in-straw code, CASBA and its members will probably have had a role in producing it and making it accessible.

Sounds like you know your building site pretty well!  You could use metal panels instead of veneer stone--a different look, but easier to install.  Still need the 2x ledger, furring strips, plywood, a house wrap of some sort, but a less thick wall, and no lath, mortar or stone.  And faster to install.

Straw bales here in S. Oregon and N. California range in price from around $5 up to $12 depending on quantity and delivery.  Be sure to use dry, dense bales. The code describes how you evaluate them, and CASBA has done a short how-to video on evaluating straw bales narrated by yours truly. https://www.youtube.com/watch?v=Fc3TI1Edbbo&t=97s


Jim Reiland
Many Hands Builders

Hi Steve,

My name is Martina and my family has also been thinking of building a straw bale, cob, or earth bag tiny home in Eastern Oklahoma. We're weighing the pros/cons of different sustainable methods that allow for passive heating/cooling and that can handle the humidity. I'm curious to hear how it's been going for you. Perhaps you'd be open to a phone call to chat about it sometime. My email is coral.puzzle.0b@icloud.com if you want to set something up.