Straw Bale Construction Forum

Arm of the Spiral

Yes! You can build your own straw bale home.

Frequently Asked Questions

This is where we go to work for you, finding answers to those questions you couldn't seem to find answers for elsewhere. Please write us or fill out the survey form on the Community Page with questions you might have. If we can't answer them, we'll do the research to find out.

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How much cornfield cropland is needed to produce one rectangular bale of straw hay (2'x2'x4'-ish size)?

How long does it take to grow that back (ecological footprinting)?

About how many bales does it take to build a standard, load-bearing house?

How do you keep them dry? If they get wet, what do you do to dry them?

What is the best hay or straw to use and what is the average price per bale?

Why install a radiant floor heating system in a straw bale house?

Where and how do you install the tubing for your radiant floor heating?

What happens if the copper pipes begin to leak at their joints?

Since the pipes are at the bottom of a thick concrete slab - does the heat even transfer to "foot level"?

Can it be used in the opposite way during Summer? To cool the floor? And does the floor even get warm enough in a straw bale home to make this necessary?

I'm building a new home in a month or 2 and was wondering if straw bale can look like a traditional home?

I would like to build a straw bale home, but any straw odor gives my wife a headache. I need to find out if you can smell the straw after the home is finished.

How do we begin? What about moisture? Why straw bale? How much will it cost?

Did you take vacation days to work on building?

How long did each process take (foundation, frame, roof, walls, windows, wiring/plumbing, interior wall work)?

Did you do the wiring and plumbing too?

How much help did you get?

How did you learn how to build with straw bales?

A question about growing and baling your own straw.

Emily responded on our web site Q&A form and had these questions:

*How much cornfield cropland is needed to produce one rectangular bale of straw hay (2'x2'x4'-ish size)?

If you're growing straw, I'd say it takes about 800 square feet to make a bale of that size. That's a conservative estimate based on my experience growing straw in Colorado.

* How long does it take to grow that back (ecological footprinting)?

It takes a season to grow the straw, but keep in mind that you only need to grow straw for an alternative purpose, mainly food. What I'm trying to say is that using straw to build your house actually has a negative ecological footprint, or a positive effect on the ecology. Farmers would otherwise burn the straw in the field, releasing carbon and pollution into the atmosphere.

Most farmers grow grains as a cover crop between other rotations. But grain farmers will combine (COM-bine) the grain and have the chaff left as a byproduct. They have a continuing supply of straw bales, for which house building is a great use. In other words, it's better to find a supply of straw bales that would otherwise have little or no use than to interrupt a crop rotation for the sole purpose of growing building blocks for your house.

A couple of footnotes: Farmers will use herbicides in the rotation process to get rid of weeds before they plant their money crop. It is good to be aware of that and discuss herbicide application rates with the farmer before you buy his hay. As a farmer, I've had success simply planting the grain as a cover without using herbicides, so I'm sure other farmers have done the same. Also, the words "straw" and "hay" tend to be used interchangeably, but they are quite different. Straw is the by-product of grain harvest and has little or no food value, making it an excellent building material. Hay is food for animals, alfalfa and grass, and therefore much less desirable for building blocks.

Thanks for your questions, Emily, and good luck on your straw bale project.

From our interactive web site, Paula asks:

*About how many bales does it take to build a standard, load-bearing house?

The answer isn't as cut and dried as the straw that will be baled up for you house. The x-factors are: how big is a standard house and how large are your bales? For Arm of the Spiral, I ordered 220 three-string bales and used about 180 for my walls. I stacked the 42-inch long, 23-inch wide bales on their side, four courses high. I liked the idea of having the straw on end to bear the load. If you thought of them like soda straws, instinctively you'd place them on end if you wanted them to hold up a weight. I believe "Serious Straw Bale" was an advocate for this method.

However, many people have built load-bearing structures with bales stacked flat (strings up and down). It's much easier to sculpt nichos and other features this way. In this case, you'd use two-string bales that are about 36 inches long.

Now, let's move on to the size of a standard house. I kind of like a 24-foot by 50-foot footprint for two people, that gives you 1200 square feet (some of which is taken up by the bales). The perimeter of such a house is 148 linear feet, arrived at by adding the length of all the sides. Divide that number by the average length of the bale you're buying and you get 49.3 bales (let's call it 50). You'll go six courses up, so that's 300 bales. Disregard window and door openings for this calculation, unless your south wall is mostly windows, which should be likely. Any additional straw you have can be chopped up for clay plaster and adobe floors, and can even be spread out along pathways during muddy season. Just be sure to rake up loose straw during the dry season as it becomes a fire hazard. Loose straw can serve a final purpose as mulch for your garden. If your straw bale source isn't close by, you might want to calculate more carefully. It is necessary to have extra so you can reject loose bales, retie bales, etc.

*How do you keep them dry and out of the rain while you are working and before you plaster them in, especially if you are a weekend worker and it takes months to get this done? If the bales get wet, what can be done to dry them?

Order your bales just before you're ready to build your walls. Stack your bales on pallettes according to the measurement of the tarp or tarps you're using. Buy good tarps. Your tarps should overhang your stack by at least three feet. Figure out a method to stretch the edge of your tarp about 8 inches away from the stack, so that water runs off the tarp and doesn't drip onto your straw. Bungee or tie down your tarps and recheck your stack often, especially after a windy day. Basically, you want to babysit that straw. If you can seal it in dry in your house and keep it that way, it will last for better than 100 years.

As I built my walls, I cut tarps down their length to about 8 feet wide. Then I tented my walls by staking the tarps away from them. I got stingy and used plastic when I ran out of tarps, and regretted that decision. Plastic rapidly decomposes under constant ultra-violet sunlight and then the wind tatters them. Decent tarps will last the months you're talking about. As a matter of fact, I still have mine and use them for various things.

I built and poured my bond beam right over the tarps. The tarps remained as I built my roof. It did take me months to finish my roof. Note that we live in the Southwest, though. I recommend making a push to get your walls under a roof -- that may be when you'll want to schedule vacation days and work like a madwoman. If you keep it simple, you can build a roof and at least get it felted quite rapidly. Trusses can go up in a day if you hire a crane, and you can get it sheathed fairly quickly. Once you have your felt securely over your plywood or OSB, you can breath a sigh of relief. Don't cut away your exterior tarps until you're ready to plaster.

If the bales get wet on their sides from a driving rain, don't be too alarmed. Just monitor them after the storm passes, giving them as much air and sun as you can. They'll dry out on their own. If a bale or bales are soaked from the top with a lot of water, you'll need to replace them. There's no sense taking a chance that you'll be sealing in a lot of moisture for the sake of a few bales and a few hours work. But better yet, spend the labor on keeping those tarps shipshape, and you shouldn't need to take backwards steps.

* What is the best hay or straw to use and what is the average price per bale?

Use straw and not hay. I'm told that rice straw is excellent, but because we're all about a light footprint on the planet, you should use whatever is grown locally. Wheat, oat, barley, etc.. Straw bales' strength is really in numbers -- numbers of square inches that bear the load of your roof. Just think, your straw bale walls share the weight of the roof with nearly three times the area of a standard stick-frame house. Most importantly, make sure the bales are nice and tight. Go to the barn and inspect the bales before you have them delivered. If you don't know what a tight bale looks or feels like, go to several farms, distribution warehouses, feed stores, or what have you and inspect bales until you educate yourself about the tightest bales in the county. A good bale should keep it's cubical form (when tossed out of a truck, for example) and it should be difficult for you to get your gloved fingers under the strings. Smell them and make sure they're not moldy. Work your hand into one and make sure it's not moist or warm (biological activity). This tells you more about the integrity of the farmer or distributor you're buying from than about the straw you'll take delivery of. You'll need to have a keen eye on the bales you accept as well.

You ought to be able to pick up a good two-string bale for between three and four dollars. Maybe less if you go straight to the farmer.

Finally, there's no shame in building a post and beam house with straw as the infill, for the purpose of insulation. If circumstances dictate it, then do it. I advocate load-bearing systems because if we collectively get good at it, we won't need to turn to forest products for that part of our houses. But over the life of your house, the reduced amount of fossil fuels you use to heat and cool it will make it sustainable.

Best of luck on your project, Paula.

Allan from New South Wales, Australia had a number of questions about radiant floor heating and the insulating qualities of straw bales.

* In articles I've read (Australian ones at least) - homeowners (generally) state that the interior temperature of their straw bale home varies no more than 8 degrees celsius between the two extremes of summer and winter. I've often wondered why so many people (especially in the States) install Radiant Floor Heating!? I've also noticed that most straw bale homes have slow-combustion stoves/ovens. This adds to my confusion of why heating the floor is necessary, if the homes are so well insulated with a temperature that remains fairly constant?

First of all, 8 degrees Celsius is about 14 Fahrenheit -- that's a fairly big temperature swing for a home. I could only imagine that happening at Arm of the Spiral after several days of cloudy winter weather (no solar gain). But even if you cut that swing in half, 4 degrees Celsius, you'd still want to have a mechanism for taking the chill off, at least if you're a wimpy American. We live at 6000 ft. altitude (1828 meters) with winter temperatures getting as low as -20 degrees F (-28 degrees C). At our latitude and climate, we enjoy a strong and dependable sun, but if outside temperature stays steadily cold or we go several days without sun, we need a backup source of heat.

So why radiant floor heating? For many of the same reasons as building in a thermal solar mass inside your home. Basically, if you heat an insulated concrete floor, you're "charging" the concrete mass with thermal energy and it radiates heat throughout the day. This time of year, our furnace comes on for about 1.5 hours early in the morning. Then the sun takes over for the rest of the day into the early following morning. If you heat the air only, you get no radiant effect. Radiant floor heating is deliciously cozy and energy-efficient.

As far as slow-combustion stoves, I assume you mean wood-burning stoves. We have a stove because we like to sit by a fire. It's not an efficient heat source, but it warms the room nicely and if we're sitting beside it, it does a fantastic job of heating us without heating the whole house.

Conclusions: While a straw bale house certainly dampens temperature swings inside, it doesn't eliminate them. Passive solar along with thermal solar panels could eliminate the need for burning fossil fuels, but still, the best way to use your panel hot water is to put it in a floor system or old-fashioned cast-iron radiators. Heat a mass, not the air. The old saying that "You can heat a straw bale house with a candle," is a nice saying, but doesn't bear out in reality.

Remember that even double-glazed windows have a single-digit R-Value compared to straw bale walls which have an R-Value of 42. Therefore, you lose heat out of them in the winter, or conversely, gain unwanted heat in the summer. Be conservative with your south-facing windows (north-facing for those of us on the Up-Over side of the world). If you've got a nice view to the shady side, plan on stepping outside to enjoy it, or plan on viewing it out a 12 by 12 inch window. Calculate the correct amount of glass area on your winter-sun-side so you get correct solar gain without over-heating. Build eaves and overhangs properly deep to shield you from summer sun. Build only as much square footage as you need. Finally, don't forget to super-insulate your roof or attic. Straw bale walls are fantastic, but heat travels up, and if you don't meet or exceed your wall's insulating qualities, you're losing that hard fought-for thermal conservation.

* When concrete floors are laid in Australia, they nail up a wooden frame (formwork) around the outer edge, then place plastic stands down that hold up a steel grid (so when the concrete is poured, the steel is in the middle of the concrete slab to reinforce, providing strength so the slab doesn't crack). I bet you do the same thing, but can you please tell me - when you put down the Radiant Heating pipes... Do you lay them right on top of the steel reinforcment mesh/grid? (Sorry - I don't know what you call the steel grid over there. We call it "rheo".)

Yes, except they are not pipes. We used a flexible plastic tubing that's state of the art, the brand name is Wirsbo. There are no "joints" in the slab -- each run is continuous back to the furnace. Several years ago, an inferior product was used in slabs that failed repeatedly, causing untold anguish among homeowners and plumbers alike. Wirsbo seems to be the ticket, but I'm sure there are other brands. We attached the tubing directly to the rheo, we call it rebar, using plastic zip ties. This is one of the few projects for which I did hire a specialist to help me get it right.

* What happens if the copper pipes begin to leak at their joints? (Especially since it snows in many places in the USA, which could cause the water to expand, cracking the pipes.) Won't the water then "wick" into the concrete and begin rusting the reinforcing mesh causing what builders down here call, "concrete cancer"?

No copper, no joints. As for domestic water, we used flexible copper tubing without joints inside the slab, as per the United Building Code. Many plumbers have gone completely to high-tech plastic throughout the house. We just didn't trust that we weren't ingesting petrochemicals, but who really knows?

* Since the pipes are at the bottom of a thick concrete slab - does the heat even transfer to "foot level"? I would have thought the ground temperature would act like a heatsink, preventing most of the temperature increase.

Yes, wonderfully. But you must insulate under the slab for exactly the reason you thought. We used 2-inch closed cell rigid insulation. You can watch this process on "You Can Do It! -- Part One". Note also that the pipes are at the center of a 4-inch slab. I'll let you do the metric conversions. haha!

* Can it be used in the opposite way during Summer? To cool the floor? And does the floor even get warm enough in a straw bale home to make this necessary?

I would imagine that you can run cool water through the same pipes. I will post this question on my site and see if anyone responds. Our experience has been that cooling the house has been unnecessary. Summer sun doesn't penetrate our windows and so the thermal mass cools off, keeping the air temperature quite comfortable. But your situation in Australia might require summer cooling. I toyed with the idea of using 'ground tubes' I forget what they're called, taking the ambient underground temperature and pumping it in to cool the air temperature in the house. My instincts are: heat a mass, cool the air. But honestly, cooling hasn't been an issue in our area. I love coming in from the hot alfalfa fields into a consistently cool and comfortable straw bale home in the summertime.

An important footnote: In retrospect, I would install an adobe floor in Arm of the Spiral throughout the ground floor. We did that in the solarium and still installed radiant floor heating within the mud. We could have tiled over the stabilized adobe as easily as over concrete, and I'm convinced now that the floor would hold up for the life of the house. Concrete uses tons of energy to make and has a big carbon footprint. Adobe uses sand, straw, and soil, along with some sweat.

Thanks for your questions Allan.

Pat Adams writes:

* I'm building a new home in a month or 2 and was wondering if straw bale can look like a traditional home?

Yes, it can! A post and beam structure with infill strawbales will give you nice square vertical corners. Undulations in the wall are all a matter of how demanding you are in tweaking the bales. I call it tweaking, you slam the bales with a battering ram or some such thing to line them up. Then cob and plaster will finish the job in getting a smooth vertical wall. Personally, I like the undulations that a straw bale wall with natural clay plaster can offer. Steve Schechter, of Mountain Solar in Gunnison might send you some pictures of infill straw bale houses that he's done. They look traditional. Mind you, siding must be plaster or stucco. Steve's e-mail is mtnsolar@gunnison.com. Tell him I sent you.

A responder to our survey form has this concern:

* I would like to build a straw bale home, but any straw odor gives my wife a headache. I need to find out if you can smell the straw after the home is finished.

Not at all. We just had guests stay at our home when we received this question. Both our guests, who have acute olfactory senses, detected no straw odor from the house. That is because there are two and three layers of natural clay over every inch of the straw bale wall. It is completely sealed from the interior air environment. Be sure you put a coat of rough plaster even behind the cabinets and so forth, just to make sure your wife will never get a whiff of that straw. Thanks for your question.

Patrick from Tenessee writes:

* My partner and I are thinking of building a straw bale house. We just don't know how to begin and we don't have a boatload of money like most of these folks seem to have who are building these sorts of houses. We also live in the south (Tennessee) and wonder what kind of effect humidity would have on a straw bale house. Also, what kind of square footage costs would we run into with an average sized home of 1200 square feet. I know this probably sounds like a lot of questions, but we are just very naive about this and wish to avoid sinking money we don't have into something that could turn out to be very expensive."

You have begun. Congratulations. If you decide to build an alternative structure such as a straw bale house, research will be an integral part of the building process. I can help you, not as an expert, but as a fellow adventurer who may be courageous enough to embark on a journey that will not only reward him with a wonderful place to live, but with an experience that he will treasure his entire life. The cost will be significant, but the rewards will be greater by multiples.

Yes, moisture is a consideration in a straw bale house, but keep in mind that moisture is a concern in any house. How many people do you know who have problems in their wood-frame house regarding mold, decay, and dry rot. Wood is just like straw -- it's a cellulose product that if exposed to constant moisture, will mildew, mold and rot. As with any house, a straw bale house must be protected from moisture. Humidity in the air is not a big problem, as straw as well as clay plaster will absorb and emit humidity according to varying conditions. Drops of water are the enemy, and if you build acutely aware of drops of water trying to get into your house, you will have as much -- no more -- success than conventional builders. The famous quote among straw bale builders: "A straw bale house needs good boots and a big hat."

So why build with straw instead of wood? Google "Life After Oil" and your answers will be in the dozens (straw bale walls have an R-factor of 42). Or consider how many human beings are on the planet now and how many trees it takes to make a conventional house. Or do some research on greenhouse gasses and "embodied energy" or "carbon footprint" and see why the use of local, sustainable resources is our obligation to future generations. If you don't buy all these "green" or "tree-hugging" ideas, then calculate your return on investment if your home heating and cooling bills are reduced by 30 to 50 percent.