Using different types of straw for strawbale walls

Hello, no one around here farms wheat, there's only sorghum or dry grass cuttings as straw bales, anyone know if those can work as well as wheat straw bales? Also I heard they don't apply any chemicals to them so I wonder if I should spray them with something beforehand (ex. insecticide) and if you can recommend such, thank you very much.

Hi Francisco,
I don't have much experience with straw bale construction, and I am mostly replying to bump this for the really smart people :)

But I do know that most wheat/oat straw has some level of being hollow in the middle that grass hay does not. I'm not sure about sorghum. I imagine those extra air pockets would add a little insulation. I doubt it would matter structurally.

It is my understanding that neither sorghum nor grass produce straw.

John F Dean wrote:It is my understanding that neither sorghum nor grass produce straw.

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These are the sorghum bales they offer me

Looks like hay to me.

Anne Miller wrote:

Well, if I can't access straw I can't do cob or straw-bale houses, which other alternatives are there apart from compressed earth blocks? I don't want to try my hand at earth ships also

Hi Francisco,
I am a big fan of hempcrete structures... though I can't guarantee its any easier to source depending on where you are.

I have never gotten my hands dirty doing Cob or Adobe.

I had a friend who made a living making adobe brick and I have watched builders building conventional homes using adobe in New Mexico.

I have also seen folks applying cob on TV.

I think the staw makes the cob work better.

As far as I remember my friend did not use straw in his adobe bricks.

This thread might help:

https://permies.com/t/44918/Straw-Substitute

These ladies did a book promotion here on the forum and I would recommend their book:

https://permies.com/wiki/87449/Mudgirls-Manifesto-Handbuilt-Homes-Handcrafted

These links explain about these building methods:

https://en.wikipedia.org/wiki/Cob_(material)

https://en.wikipedia.org/wiki/Adobe

https://en.wikipedia.org/wiki/Hempcrete

Hi Francisco, there's a really good explanation of the difference between straw and hay at this post from 2022:  https://permies.com/t/183858/Hay-Straw-straw-hay-building#1471147, and it might shed some light on whether sorghum is suitable as a building material.

Sorghum is considered a grain, but I don’t believe the stalks are straw like—you’ll want to research this.  Sorghum, like corn, is in the grass family.  Corn stalks are nutritious enough to be used as animal feed, which means they might also attract all manner of critters to live in your walls.  

Several countries have building codes that define what "straw" is.  For example, in the United States the IRC Building Code Appendix AS Stawbale Construction defines straw as "the dry stems of cereal grains after the seed heads have been removed.”  Section AS103.7 Types of straw: “Bales shall be composed for straw from wheat, rice rye, barley or oat.”  I have used triticale bales for building—a cross between wheat and rye.

The commentary to that section reads “Bales made of straw from the five named cereal grains have been successfully used in modern strawbale buildings on six continents since 1990. Straw is an agricultural byproduct baled after nutrient grains have been harvested and is commonly used for livestock bedding and erosion control.  Baled grasses such as hay or alfalfa must not be used.  They are cultivated and baled as life stock feed, are baled green, contain nutrients that support active decomposition by micro-organisms and are unacceptable for building.”  You can obtain a free copy of this building code from the California Straw Building Association's website, www.strawbuilding.org.

Even if your area doesn’t require building permits or inspections, or hasn’t adopted this particular IRC code (or whatever codes apply in the country you live in), it’s wise to follow a beaten path unless you have the time and resources to replace walls made of baled materials that one day fail.

Good luck!

Jim
Many Hands Builders

I actually found a building manual done by local government which suggests using wheat or rice straw but says sorghum "straw" can be used if it doesn't contain any seeds, apparently there were some projects done as demonstration but I can't find the exact location to ask around, I think I'll take this in good faith and try to go ahead with a small sorghum straw structure to see if it's viable, thanks everyone

Sorghum straw might be OK, actually, although I've not heard of any projects using it.

https://www.researchgate.net/figure/Chemical-Composition-of-Sorghum-Straw-and-Bagasse_tbl1_317429273 - broadly comparable to wheat straw, although less lignin. I'd suggest getting a few bales and subjecting them to mistreatment before committing, though. See how they get on.

Not the same thing at all, but there's a miscanthus bale project ongoing that seems positive so far - https://www.terravesta.com/news/the-worlds-first-miscanthus-bale-house/ . So plenty of room for experimentation, still.

[quote=Nick I'd suggest getting a few bales and subjecting them to mistreatment before committing, though. See how they get on.


By mistreating them you mean try to compress them or leaving to weather out in the open? Apparently sorghum straw us the same material they made old brooms out of (at least here) so I think it can hold pretty well, also wouldn't lime or clay plaster protect from degradation?

Francisco Reyes wrote:
By mistreating them you mean try to compress them or leaving to weather out in the open? Apparently sorghum straw us the same material they made old brooms out of (at least here) so I think it can hold pretty well, also wouldn't lime or clay plaster protect from degradation?

Yeah, subject them to mechanical and material stresses, see how they burn, how they react to getting wet, how quickly they attract mould or decompose, how water moves through them, whether rodents like to eat it, etc.

In an ideal world, the straw never gets wet and never gets set on fire, but with wheat or barley straw, it has some tolerance and rot doesn't tend to spread; you can hack out affected sections and replace them after fixing a leak. You can also get away with it getting some rain on it during the build process itself.

Is all that true of sorghum? I don't know, and I'm not sure if anyone does yet ^^.

Nick makes some really good points--build a wall and subject it to some weather!  Building with more natural materials has advanced as far as it has because people were willing to take chances with some unknowns.  We don't usually hear about the failures--they tend to slowly decompose and disappear (which is a good thing compared to building with "forever" toxic materials!).  

When I grew up in the upper middle west of the United States I heard stories of how farmers in previous generations insulated their stick-framed farm houses with corn cobs, shredded corn husks, horse hair, wood chips and saw dust, dried oak leaves--anything on hand to fill the empty cavity and offer some insulation against the bitter cold winters.  It must have worked because I saw evidence of these no-longer used insulative materials when I poked around the old farm buildings in my community.  

If you can manage a small structure, or even a test wall, and keep tabs on the sorghum bales' condition through a few weather cycles you'll have some answers.  Did they settle?  Decompose?  Attract rodents or insects?  If successful, others may follow your path and who knows, perhaps one day sorghum will join the other grain straws listed in various building codes.  

But do some research first.  If sorghum stems are used as animal feed some university somewhere has published research on its nutritional value compared to other things like corn stalks and straw (apparently straw is an animal feed in some places).  That's an indication of how suitable it is as a building material--if it's good to eat, it's probably not good to build with.

Jim
Many Hands Builders

Well, I was planning to make a small straw bale house with concrete posts and a small wood structure to keep the bales in place, I was wondering how easy is it for any rotting in the straw to move on to the wood? thus forcing me to trash everything. I've heard of people building concrete columns to support the roof and then tying the straw to it that way even if the walls rot I can just tear them down without trashing everything.

If the rotting straw is hard up against the wood for any length of time, it will spread to it, which is why I'm interested in whether moisture and rot spreads through the sorghum or not.

I did come across https://journal.augc.asso.fr/index.php/ajce/article/download/1455/933/ - so there is some research out there on sorghum in building. I think if it were me, I'd be willing to at least trial it.

The deterioration of cellulose material like straw would continue so long as there was a source of sufficient moisture and something for microbes to eat.  Keep the walls dry (good boots, good hat, and a coat that breathes), and if the straw goes in dry, it won't decompose.  At the International Straw Building Conference held in Colorado back in 2012 someone brought a straw bale that had gone into one of the "Nebraska style" homes in Nebraska built around the turn of the last century--it had been obtained during a remodel.  The bale was at least 100 years old and looked as fresh as had it been placed in the wall the day before.

Where I work in S. Oregon there are at least one-hundred permitted straw bale homes, some of them approaching thirty-years old.  I know that's not very old, let alone compared to the service life of buildings in Europe, but many of these structures were built shortly after the straw bale building revival in N. America picked up steam in the early 1990s.  

Builders didn't have a lot to go on back then, and as many weren't built by experienced contractors with at least a notion of how to keep water away from walls...well, mistakes were made.  As these straw bale homes came up for sale and original owners wanted repairs made, or prospective new owners wanted an assessment of the walls, I was hired to take a look, and often do some repair work.  Whenever I found moisture damaged straw it was due to poorly flashed windows and doors that received seasonal wind blown rain, a roof leak, a gutter downspout that dumped water onto a wall, a tall wall with insufficient protection from a roof, etc.  

Only parts of the bale wall were damaged--usually the exterior surface nearest the water source--and none of the surrounding wood framing.  

What likely happened was that during our five-month-long rainy season wind-driven rain would find a way through these poorly flashed joints or overly-exposed lime or cement plastered walls, revive the microbes already in the straw when it was placed during the bale stack, which became active until our warm dry summers drew the moisture out of the walls and the conditions for microbial activity ended until the next rainy season (or the leak was fixed or the wall exposure resolved).  The wood framing wasn't damaged, probably because the moisture source was temporary, and since wood is so much denser than straw it resists decomposition better.  Had the moisture source been constant....

If using concrete columns to support roof loads is a common building system in your area, by all means follow that lead--others have discovered this it's a good idea.  Just make sure to isolate the columns from ground moisture so water doesn't rise into the wall via capillarity.  But if builders generally don't use concrete columns, I wouldn't do it for the reasons you mentioned.

Just make sure:

--your bales--whatever cellulose material they are made of--are well elevated above grade (in the U.S. the building code requirement for straw bale walls is at least 8"),

--there's a moisture barrier separating the bales from ground moisture (which is usually achieved by placing that barrier under rot-resistant wood sills that are filled with some kind of drainable insulative material).

--the building design has a sufficient roof overhang to keep wind-driven rain from wetting the walls, and if there are no gutters, the roof drops rainwater far enough from the wall to prevent it from splashing onto it when it hits the ground.

--the walls are protected by a vapor permeable ("breathable") siding like lime or clay plaster, or a combination of a plaster coat with a rainscreen siding system,

--doors, windows, and other openings in the wall are flashed against water intrusion

--and that you stack the bales dry (under 20% moisture content, and preferably closer to 10% MC!).

I don't think you mentioned where you plan to build, but know that straw bale structures have been built in over fifty countries, many of them very unlike the arid American West where building can be done nearly year-round, and the bales are almost always extremely dry when stacked.  Wetter and more humid places will impose more challenges on a building schedule, but there are well-designed, well-built, and long-lasting straw bale buildings in wet coastal N. California, Oregon, Washington, British Columbia, S. Alaska, and many other places.

That says something!

Jim
Many Hands Builders