The Difference Between Hay Bales and Straw Bales

Here is a quick primer on the subject sparked by the following email I recently received. Thanks Josh for the question. This may be obvious to some, but I am no longer surprised by how many people have this very same question. I often hear people use the wrong name for this technology. I hear them talk about hay bale construction or strawbail. The misspelling I can deal with, but the inclusion of hay in the idea of home construction is a problem. In fact, I even heard a builder, claiming to be a straw bale builder, describe his model “hay bale house” when I spoke to him at his booth at the Green Building Expo in San Francisco last year! YIKES!!! I hope that the builders out there know the difference and understand the importance of working with straw. For those many others who have the same question, here’s the breakdown. Actually, here’s the original email question first, then the breakdown.

Josh wrote:
I’m sorry to ask such a simple question but I would really appreciate it if you would explain (on your blog or in a reply email to me) why exactly you cannot use hay to build with. I have ready access to a LOT of hay that is the same price or cheaper then straw in my area. I would like to use some to build a few small structures but I cannot seem to find much information at all about hay. I have read the available information and thus have had some very simple answers but I’m curious if you would provide a relatively thorough answer to
the hay vs straw debate. I need it cleared up so I can share the information myself! Thank you very much! btw – I’m subscribed to your blog and love it!

Here’s my response:
Hay bales are a food source. That is the first and perhaps most important difference. Hay is actually a plant that is cut when it is alive and full of grain. The purpose of the hay is to feed animals. Straw, on the other hand, is simply the stalks of standing plants that contain no grain. The grain is harvested from the plants by a machine that cuts it off of the stalk. The grain is then removed from the field and the stalks are left to die, standing. Once they are totally dead and mostly devoid of moisture, they are cut, raked, and baled. The baled straw has multiple uses. It can be used as animal bedding, erosion control, home building, and more. One thing it is not used for is food. So, the first question to consider is: do you want to build your house out of a food source or something that will not be eaten? I prefer the latter myself.

The next point to be considered is the moisture content of the bales. Pretend that the whole food source thing didn’t matter, just for now. When hay is cut, it is a live plant. That means it has moisture in the entire plant. It is left to dry on the field for a short time and then raked and baled. In that time, some of the moisture leaves the hay, allowing it to be baled without decomposing. We have all heard of bales spontaneously combusting, right? Well, this is due to bales having too much moisture in them. They start to decompose on the inside and that creates heat. That heat increases as the decomposition process increases (cyclically at this point) and then the bales burst into flames from excessive heat. This is a situation where there is obviously too much moisture, yes, but it proves the point I am making in a dramatic fashion. Straw bales have very little moisture content in them when they are baled. This is another difference in material. The lower the moisture content, the less chance of damage to the bales once in the house by either mold or fire from decomposition. In fact, decomposition and mold growth cannot happen in the straw as long as the moisture content is kept below 20%. That is quite high by the way. Most of the bales I use register around 8-9% moisture content to give you an idea.

Finally, the inclusion of the moisture and the seeds can cause something else within the structure that is neither fire nor food: growth! I have seen cob walls where the straw used in the mix had a lot of seed material wrapped up in it. Two days after the plaster was applied, the entire wall started to grow grass! The owners thought it funny, which it was at least to look at; however, this was indicative of a big problem: they had seeds in their walls. This can attract all kinds of pests from mice to cows. In the cob, it was less of a problem but in a bale wall, it could be a disaster.

So, no food, low moisture content, no growth is what makes straw the ideal product. As a great bumper sticker I bought from CASBA (the California Straw Building Association) a few years ago reads: “Hay is for Horses. Straw is for Houses.” I couldn’t say it better myself!

38 Responses to The Difference Between Hay Bales and Straw Bales

  1. Josh Houghtelin Mon, October 29, 2007 at 12:03 pm #

    Thank you so much! I am now very well informed about the difference in choice. I do of course have quite a bit of hay for our horses and that is precisely where it will continue to go. To the horses. A sod roof would be pretty cool but I’m not so sure the wife wants grass coming out of the walls!

    Thanks again for clearing this up for me. Have a beer/lager/coffee on me!

  2. Tommani Sandoz Sat, January 26, 2008 at 11:05 am #

    I know well the difference between hay and straw, but what I don’t know is the preferable TYPE of straw! Someone told me tha Oat Straw is the best choice and I see you like the organic Oat Mkeal Stout, but what about wheat steaw or barley straw? Can these types of straw be used also? Does one have better insulating properties than the others? I assume the bigger the airspace within the stalk would be the deciding factor but have never seen or read about this variable. Thanks for all the great information, Yours in the Green Zone, Tommani R Sandoz

  3. Andrew Sat, January 26, 2008 at 9:23 pm #

    Tommani,
    I believe that the best bales are those that are locally available to you, as long as they are dense, dry, and uniform in shape. Wheat, barley, oat, rice, hemp, cardboard…anything that can meet the requirements for density, moisture, and shape will work fine.

  4. Lynn Z. Mon, October 20, 2008 at 4:50 pm #

    Andrew,
    We are putting some great straw in our walls now but every once in awhile we run into a bale with what appears to be some dried grass in it. Those bales appear green in color here and there, within the obvious straw. Is this an issue? Should we avoid those bales and remove the ones that got put in the wall before we plaster?

  5. Andrew Mon, October 20, 2008 at 8:07 pm #

    If you can easily remove the bales with the obvious grass, I would. I would also not use any with green grass in them moving forward. It will likely not be a problem, but why take the risk? Good catch!

  6. Clyde Scott Wed, November 5, 2008 at 3:28 pm #

    Andrew, we have access to hay that is clean, but to old to be used for feed. I can get it for much less than straw. Local straw dealers charge more than for hay. The hay I am describing comes from costal bermuda, which is a very course grass that produces no seed, as it is sterile. Not moldy and very dry from many years in the cover of a closed barn. Why would it not be usable?

  7. Andrew Tue, November 11, 2008 at 1:16 pm #

    Hmmm. If it is hay, it is a food source. I would suggest you not use it even if it is dry and without seeds.

  8. Jill Fagen Fri, January 9, 2009 at 11:29 am #

    I am looking into building a Strawbale house in North Texas and am concerned about ants, fire ants especially. Will they be a problem?

  9. Andrew Sat, January 10, 2009 at 6:37 am #

    Hi Jill. The ants should not be any more of a problem in a bale house than in a conventional house.

  10. Jane Collins-Philippe Fri, January 23, 2009 at 3:47 am #

    Hello, I was very happy to discover your website today and would like a bit of advice if possible. I am going to have a wooden house built on my land in France. The builder suggested using loose straw as wall and floor insulation. I’ve read some comments from someone on another website who did that it turned into somewhat of a problem both in terms of time and money spent. Also he said that plasterboard had to be used to meet fire regulations (in the UK) and the straw had to be boxed. Any ideas or suggestions?

    Many thanks,
    Jane

  11. Andrew Fri, January 23, 2009 at 9:55 am #

    Hi Jane. I would recommend against using loose straw in the walls and floor as it is not the best insulation per cm available and therefore would likely end up being a waste of effort and money. I would suggest cotton insulation if you are trying to stay green. Loose straw is a fire risk and has a relatively low R-value per cm.

  12. Jane Collins-Philippe Fri, January 23, 2009 at 4:10 pm #

    Hello Andrew,

    Thanks for your helpful and speedy response. I am a real novice in this field. Could you give me an idea of the cost of cotton insulation and in what application form it comes? Is it appropriate for roof, floor amd wall insulation? I’ve never heard of it being used here in France but of course that doesn’t mean it isn’t.

  13. Andrew Sat, January 24, 2009 at 12:29 pm #

    Cotton insulation is very versatile. Check out this website for a bunch of good information about the product. This is just one of several companies who make cotton insulation. http://www.bondedlogic.com/

  14. Kylee Sat, November 7, 2009 at 11:32 pm #

    This is actually so interesting!
    I have a college assignment on ‘hay bale construction’ and couldn’t understand why i could only find info on straw bale… hmmm… seems colleges also make mistakes – and that is scary!

  15. Andrew Sun, November 8, 2009 at 8:43 am #

    That’s funny! You ought to do well on your assignment since you can show the college that you know more about the technique than they do.

  16. Pat Sun, January 31, 2010 at 11:01 am #

    You see the “square” and the hugh “round” thingys in the fields after harvest. Is one more for straw than for hay? Thanks

  17. Andrew Morrison Wed, February 3, 2010 at 11:19 am #

    It depends on what’s harvested. The large round bales can be either hay or straw. It’s best to ask the farmer directly. Either way, you want smaller bales, so start by finding a good local source of 2 string or 3 string bales. You can ask your farmer supply store for leads or go straight to the source by watching fields as they bale and speaking with the farmer directly. I prefer the second, more direct option.

  18. Pat Thu, February 4, 2010 at 2:16 pm #

    You wrote that the large round bales can be either hay or straw, so can the square bales be either, also?

  19. Andrew Morrison Sun, February 7, 2010 at 7:59 pm #

    Sorry. Yes, they can be either as well.

  20. Chuck Hall Tue, March 16, 2010 at 7:48 am #

    Do you know of any architects or engineers in the Upstate South Carolina/Western North Carolina region who may have experience working with straw bales? I cannot get a building permit without one, and so far I haven’t been able to find one.

  21. Andrew Morrison Tue, March 16, 2010 at 1:34 pm #

    I don’t of hand. I’d suggest you contact the folks on the links below as they have completed homes in South and North Carolina and could have some information that will help you. Short of that, you can contact Chris Keefe (chris@organicformsdesign.com) and see if he can help you as a designer. He has engineering connections and lots of SB design experience.

    South Carolina: http://sbregistry.greenbuilder.com/search.straw?lcou=United%20States&lsta=SC

    North Carolina: http://sbregistry.greenbuilder.com/search.straw?lcou=United%20States&lsta=NC

  22. Melanie Hayes Mon, August 8, 2011 at 4:09 am #

    1) Wonderful to hear your site on Straw Bale homes.

    2) VERY IMPORTANT, PLEASE INCLUDE THIS TO EVERYONE YOU TALK TO ABOUT STRAW BALE HOMES.
    (KISSING BUG DISEASE )( Triatominae) (CHAGAS DISEASE )(American trypanosomiasis) ( Caused by the flagellate protozoan Trypanosoma cruzi. )

    This is a bug that has been only in Mexico and South America. It has spread into southern 1/2 Texas, New Mexico, Arizona to California and I do now know how far toward Florida.

    THE KISSING BUG IS A BUG THAT LIVES IN MUD AND STRAW OF HOMES BUILT ( MUD & EARTH IS THE PROBLEM, NOT STUCCO OR PLASTER) . THE KISSING BUG LOVES CARBON DIOXIDE. IT COMES OUT AT NIGHT AND GOES TO AROUND THE MOUTH OF CHLIDREN AND ADULTS. IT BITES AND SUCKS BLOOD. ( The person never feels the bite or the crawling ) THEN SADLY JUST AFTER THAT IT’S INTESTINES MOVE AND IT HAS A BOWEL MOVEMENT. IN THE INTESTINES OF THE BUG IS A BACTERIA THAT MEANS DEATH TO HUMANS. IT GETS IN BLOOD STREAM FROM THE BITE SITE. IT SLOWLY OVER YEARS DESTROYS THE HEART/ INTESTINES OF THE PERSON AND CAN DESTROY OTHER AREAS. THEY CAN SLOWLY SHOW SIGNS OF ILLNESS AFTER SEVERAL YEARS OR DROP DEAD SUDDENLY. ( The parasite in the blood can be killed by antibiotics and the person does not have to die. The problem is knowledge you have it. After to many years it is to late and even with antibiotics to kill off the parasite the person will die, but they can live longer if treated to kill parasite in blood stream. THE KEY IS PREVENTION.. WALL CONSTRUCTION NOT USING MUD OR EARTH) ( PLEASE Google: 36 y/o man drops dead riding lawn mower on California golf course. No symptoms of illness )
    WHY I TELL YOU THIS IS BECAUSE THE STRAW HOMES MUST NOT USE MUD OR EARTH OF ANY KIND. ONLY STUCCO ETC. THE BUGS LIVE IN MUD PART OF STRAW MUD HOME.) NOTE MANY MIGRANT WORKERS COME FROM MEXICO ETC, AND DO NOT KNOW THEY CARRY IT. THE BUGS ARE SPREADING. THEY DO NOT JUST STAY IN HOT/ WARM ENVIRONMENTS.

    ( THINK ABOUT THIS! IF SEEDS CAN SPROUT THROUGH DRIED EARTH COVERED WITH PAINT, THE KISSING BUG CAN CRAWL THROUGH ALSO. IF ONLY STUCCO ETC IS USED, NO ENVIRONMENT FOR THEM TO LIVE AND MOVE IN.)

    I FIRST HEARD ABOUT THE KISSING BUG DISEASE THROUGH WORLD VISION ,THAT WAS GOING INTO CENTRAL AMERICA AND HELPING TO REPLACE MUD STRAW HOMES WITH MATERIAL THAT WOULD NOT ALLOW GROWTH OF THE KISSING BUGS.

    THANK YOU FOR YOUR HELP.
    PLEASE LOOK UP EVERYTHING ABOUT IT. ALSO CONTACT YOUR STATE CENTER FOR INFECTIOUS DISEASES CONTROL AND ASK QUESTIONS FOR FREE. ( THE MAIN CENTER INFECTIOUS DISEASES Is IN ALABAMA, I BELIEVE. THEY DEAL WITH THE WHOLE USA ) PLEASE ASK EVERYTHING THAT COULD BE DONE TO PREVENT PROBLEM WITH STRAW HOMES.

    I THINK STRAW HOMES THEY ARE A WONDERFUL IDEA. IT WOULD ALSO BE A WONDERFUL THING TO BUILD YOURSELF A STRAW HOME CABIN FOR RETREAT AREA OR CAMPING.

  23. Andrew Morrison Thu, October 13, 2011 at 9:03 am #

    Thanks for the warning and insight. From the research I have done, it seems that these bugs are most common in unkempt homes. Yes, they like the idea of mud plaster, but my sense is that they are more common in houses that are messy, or in fact DIRTY (walls included). It sounds like it is typical in Central and South America where living standards are lower. Not to say all of Central and South America has lower standards. What I mean is: in the areas where the standard is lower, there is more infestation. I think the best thing is to keep the house clean and be watchful for these little bugs. In many cases, they will not be an issue, but it only takes one carrying the disease to infect you. Be careful, but don’t panic. :p

  24. Chris Anderson Sun, January 15, 2012 at 1:40 pm #

    Clarification: Straw is a food source for farm animals… just not in the same way, or extent that hay is.
    Think of it as a supplementary source, sort of like pasta, in a meal–it is there primarily as filler, whereas the fruits and vegetables are the primary nutrient source in a good meal. You won’t live well or long on pasta only, but you will live long and well on a fruit and vegetable diet. That’s straw vs. hay.

    That said, when harvesting a grain crop, most farmers “chop” the straw and spread it over their fields (that’s what is coming out the back end of a combine). While it would be generous to say they do this to add value back into their land–indeed, land that is constantly baled does lose tilth and nutrient balance over time and is more subject to erosion–the real reason is that it is easier to seed into that field the next crop year if there isn’t a bunch of “trash” standing on it. Hay is ALWAYS baled for feed. Straw is baled mostly for bedding, but is also fed to livestock; but it is primarily just a way of dealing with an annoyance!

    Insulation value:
    When I break a piece of straw in two, I find a hollow tube. Cutting a piece of hay in two I find a more solid structure. Since dead air is the actual insulator, it stands to reason that for a given quantity, straw will be a better insulator than hay–if you don’t crush the life out of it.

  25. Kimberly Thu, April 19, 2012 at 7:21 am #

    I have a straw bale house and noticed that there are some little bugs that almost look like fleas but are not. Are they attracted to the walls somehow and how do I get rid of them? Any help or suggestions please.

  26. Andrew Morrison Sun, April 29, 2012 at 6:37 pm #

    Check out the post about psochids here at SB.com. That’s what they most likely are and they are telling you that there is moisture in your wall. Could be from plastering if the house is new or a leak. BEST of luck discovering the cause. Once the walls dry out, they will be gone.

  27. Pastor Man Sat, June 23, 2012 at 6:27 pm #

    GREAT!
    BEYOND GREAT!
    QUESTION
    1. ARE YOU EVER INVITED TO A LOCATION, TO STAY ON SUPERVISOR
    OR GENERAL CONTRACTOR? IF SO, BESIDES THE HOTEL & MEALS
    WHAT IS YOUR CHARGE PER DAY? IF NOT, ‘ BOO-HOO’ WHICH BRINGS
    ON . . .

    QUESTION
    2. CAN YOU ADVISE OF SOMEONE WHO HAS MULTIPLE STRAW HOMES
    BUILT UNDER THEIR SUPERVISION?

    I remain in absolute AWE for certain

    Thanks so much

    The Pastor

  28. Andrew Morrison Wed, July 4, 2012 at 12:05 pm #

    I do a lot of consulting for people and the cost varies from an hourly rate to an overall project rate. I don’t stay on site for more than a week at a time as I have family and other business commitments to attend to. My hourly rate is $50/hour and my weekly rate is $3000/week (if I stay on site) plus travel expenses. I usually use the week long time to train a small crew to continue the work while I am gone. I also offer year long consulting and other packages ranging from $5000 and up depending on what’s involved.

    I can do a lot from a consultant’s point of view and usually for a relatively inexpensive cost if you can provide the builders/labor force. I can train them, they can do the work. It’s the best of both worlds.

  29. Julie Wed, November 28, 2012 at 11:45 am #

    April Magill is an architect that works with straw bale construction, she has a website http://www.lowcountrynaturalbuildings.com

  30. Richard Henkle Fri, March 29, 2013 at 4:05 pm #

    Do Not build with Hay. Because of the moisture content and energy inside of a hay bale, heat is given off. Barn fires used to be a common occurrence in improperly ventilated hay barns. Encasing Hay with any kind of moisture or food energy into a wall could be potentially dangerous. I used to build hay fort structures in our barns for fun. We fed the hay out of course. The point is: Hay has too much energy and is for food. Straw is dry, essentially inedible, and can even be mixed with cement to strengthen it.. I have seen this done and am very happy with the results.

  31. Andrew Morrison Fri, March 29, 2013 at 4:19 pm #

    Correct Richard except don’t use cement as plaster. It causes way too many problems with moisture issues and rot. Stick to lime or earthen plasters. Natural hydraulic lime is my favorite.

  32. john Fri, December 13, 2013 at 1:35 pm #

    Great answer! Really cleared up the problem concisely. Thanx!

  33. Janiehowardknudsen Tue, May 13, 2014 at 2:54 pm #

    I’m so happy to have found your webpage!
    I am wanting to lasagna compost my front lawn (drought in Ca!) for the summer. I am a city girl and cannot tell if the bales in my back yard, used to stop my daughter’s arrows, are hay or straw. They are three years old and have decayed but was hoping to use them (4 bales) for the composting project…is there a way to tell the difference?

  34. Andrew Morrison Thu, May 15, 2014 at 5:02 pm #

    Chances are they are straw because straw is less expensive and typically used for things like archery targets. That said, you can look for obvious seed heads and investigate whether those heads (if present) have seeds in them or are stripped away. If they are stripped away or absent, then you have straw. If they are full of seeds, you have hay.

  35. Ingrid Tue, October 28, 2014 at 3:54 pm #

    I just got three bails of hay for our three backyard chickens from a local halloween pumpkin patch and read on this site about the dangers of building with mud and straw- ” kissing bugs”! are we in any danger if the bales ( straw, I think) are under our back porch with by the coop? the bales are still tied to the top of my car and I’m considering taking them back!

  36. Andrew Sun, November 2, 2014 at 10:42 am #

    I would not have any worries whatsoever…

Trackbacks/Pingbacks

  1. Hay Bales vs Straw Bales | Ecocentric Design - Fri, September 9, 2011

    […] A prospective client with whom I have been talking about using straw bales to construct a little cabin to cut costs, asked me if she could use haybales instead. She owns a farm and can make haybales herself. I didn’t think it is a good idea because haybales could attract mice and other rodents into the wall. I did a little research this morning to verify my opinion and found this article, which I would like to share here: The Difference Between Hay Bales and Straw Bales. […]

  2. Hay vs. Straw – What’s The Difference? - Wed, September 21, 2011

    […] HERE for The Difference Between Hay Bales and Straw Bales, from Andrew […]

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