Straw Bale Houses, Not Hay Bale Homes: Why it Matters So Much

Written by Andrew Morrison

tall stack of straw balesHere 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. It’s straw bale houses, not hay bale homes.

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!

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67 Responses

  1. Hi. Im planning to build a staw house for me and my wife here in Mexico, there is little information about using sorghum straw bales wich is very abundant in location would you recomend usin sorghum for construction? Thank you!!

  2. Hola Juan. Creo que sorghum es bien. Nunca lo he utilizado, pero parece que funcionaría. Hope it is okay to practice my Spanish. I’m learning. 🙂 In case I didn’t say it well…

    I think Sorghum is good. I have never used it but is seems like it would work. The thicker the stalks, the harder it will be to use because of resizing bales. Good luck.

  3. I have an elephant made with straw and roped together. I would like to put this in my yard but, I cannot find anything that will tell me how to protect this from the elements.
    Will this withstand the elements in Florida with no preparation?

  4. I would not put it in the weather without a roof to protect it, personally. Straw is weather resistant to some extent, but prolonged exposure to sun, oxygen and water will cause it to rot, as is true of any organic material.

  5. Hi Andrew,
    I’m wondering if you know whether straw bale can cause an allergic reaction if used in a cabin. My son is highly allergic to wheat,oats and barley and also has asthma induced by environmental allergies. He is going to a camp field trip and I just read that the cabins are built from straw bale. Does straw bale still contain the good proteins from the grains used?

  6. Hi Martha. It is different for everyone as each person’s allergy is different than the next. That said, I have not heard of people having issues with SB homes in terms of allergies. The bales are sealed behind a thick layer of plaster, and as such, do not have direct contact with the habitable space. I would not suggest your son be on site until the plaster is complete as the loose straw is irritating to almost anyone who breathes it.

  7. Hi Martha,

    I am considering using straw bales for walls for a shed I am building. The walls are 4m high and in total including the 3 sides 44m long. One side is left open. The roof and structure is sound, and so all I need is a way to block up the sides.

    I like the idea of straw. May I please pick your brain and ask a few questions.

    1. With what do you plaster the straw?
    2. Any ideas on an affordable method to secure the bales from falling?

    If I can get this to work it will be a very very exciting day. Imagine the possibilities.

    I hope you can help.

    Kind regards
    Matthew van Lingen.

  8. Hi Matthew. I think this message is intended for me and not Martha so I’m going to jump in. I plaster my walls with Natural Hydraulic Lime Plaster. In regards to your second question, there are a lot of construction details that need to be considered, so it’s not as simple as me saying “do this” and you’ll be fine. I am a firm believer in using 2″ x 2″ welded wire mesh to keep my walls tight and secure. Again, there is a lot to that answer that isn’t covered here. You can find the details on the site, in our DVDs, and at our hands-on classes. Good luck with your project.

  9. Andrew I am thinking of using straw bales to put as a wall for my fifth wheel to keep the wind out since I live in my fifth wheel. But I live in an RV park and cannot make Miss do the E straw bales can they come wrapped and will it mold during the winter

  10. Hi Ana. I hear you. You can do one of two things:
    1. Place the bales temporarily in position and replace them each year. They will start to rot a little, but not so much that it causes problems.
    2. Create a permanent installation where the bales are placed on a raised “foundation” (could be pressure treated wood framing) and then plastered. This will provide adequate protection for many years. You could even wrap them in tyvek and then wire mesh to provide extra water resistance.

  11. hello I just want to know the different uses of hay bales could you please assist me to find out the different uses of hay bales

  12. Just one point, we do feed straw in Norther Ireland ,it is mixed with silage and or grain to make a mixed forage to feed cattle with in Winter.

  13. Hi Andrew,

    I am considering using straw bales, enclosed in leather or canvas covers as modular sofa sectionals indoors. Is there a risk of mold or pests if the bales have been properly dried and inspected.

    Thanks and great content!

  14. Good day Andrew.
    I’ll get straight to the point. Can I use sudan bales for building my shed walls. Long story but i can’t find any more straw bales and I need to get enough to finish. Will sudan bales work ok?

  15. Hi Anthony. I would not recommend that as Sudan Bales are a live crop, grass. That means that they have food value and as such could invite problems with rodents and other critters. If you are only in need of a few bales to finish your project, I would recommend going to a farm supply store and buying bales through them. They will be expensive, but the result will be less expensive than adding a food source bale to your home. Good luck.

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