I am often asked how many bales will be needed in my client’s straw bale houses. I too have to know the answer to this on all of my own projects. There are a number of ways to calculate the bale requirements. Click the following link (www.strawbale.com/articles/straw_bales_house.html) to see an article I just wrote for www.strawbale.com on the three most commonly used ways to calculate bale quantities for your straw bale house. My preferred method, the second of the three listed, is given here.

**Calculate the number based on square footage of the wall surface area**

One way to estimate your bale needs is to go a bit more in depth and calculate the number based on square footage of the wall surface area. In other words, you calculate the total lineal feet of straw bale wall and then multiply that by the height of the walls. This yields the square footage of wall surface. For a gable roof, measure one half the width of the building at the gable and multiply it by the total height of the gable end. That will give you the square footage of the entire gable as if you took the two triangles and glued them back together in the shape of a square at each gable end.

You can then remove the square footage of window and door openings from this number. Once you have all of the openings removed, divide the total square footage by the square footage of your bales. For this, consider a 14″ tall by 36″ long bale would have 504 square inches or 3.5 square feet of bale surface area. This will give you the exact number of bales you will need to build the structure.

## 11 Responses

At 4:56 PM, Machelle said…

My fiance wants to have a crawl space under the house for the plumbing and the heated floor system so he can get to the pipes easier if they should bust or something. He wants the space to be at least 18″. What do you suggest.

Machelle Bice

Maud, Ok

At 4:58 PM, Machelle said…

How far out should you place roof overhangs on a haybale home to make it passive solar, and what type of extra supports do you think we would need.

Machelle Bice

Maud, Ok

At 2:12 PM, Andrew Morrison said…

Machelle,

The exact dimension for the roof overhang actually depends on the area in which you live. The latitude of your area determines the angle of the sun in all seasons and thus is used to calculate exact sizes that will block the sun in the summer while allowing it in in the winter. That is something your local power company may be able to tell you, i.e. the angle of the sun in your area. If not, you can go on line and look into simple sun charts like the one at the following link: http://www.esru.strath.ac.uk/Courseware/Design_tools/Sun_chart/sun-chart.htm. They can be a bit difficult to use if you are not accustomed to them, so it is best to try and find the local information first. I typically use an overhang of 2-3 feet depending on the design. It is also a good idea to use an overhang for the first floor even if there is a second floor above it. In other words, be sure to have two roof systems or a deck that will protect an otherwise large expanse of wall.

In terms of the floor framing, you can build a bale house on a standard crawlspace floor system as long as the size and spacing of the floor joists accounts for the extra load of the bales (about 40 pounds per square inch additional dead load).

Andrew

I want to estimate the vertical load on a residential building load bearing straw bale wall but doesn’t know how to go about,

That is something for an engineer to tackle. Those types of calculations are outside of my reach.

Hello,

My husband and I are thinking of building a straw bale house in the mountains and I wanted to know if you could build on a pier foundation. Thank you for all the information.

Hi Gigi. You can indeed build on a pier foundation. There may be some engineering involved to make sure all your loads are properly distributed, but it is certainly an option for you.

Hey Andrew a bit more math than Im capable of but I am interested in your ECO1500 plan and could use an estimate of how many bales I could assume in order to purchase a year in advance/w storage, and also has this plan been built/build cost?

many thanks for your input

Hi Monique. The best thing to do is figure out which bales you plan to use (2-string or 3-string), and in which orientation (on edge or flat). I build with my bales on the flat; however, Touson (the designer) typically designs with his on edge. The reason this matters is that bales are wider than they are tall, so if they are placed on edge, you will need less bales overall. Another detail to consider is the height of your wall. If you plan for an 8′ ceiling, you will need less than if you push it up to 10′ ceilings. That’s probably obvious, but worth noting nonetheless. Next, you will want to calculate the square footage of the bales you end up using. Check out the examples below. After that, calculate the total wall square footage (length of wall x height of wall). I do NOT deduct anything for windows and doors and instead assume a solid bale wall. Once you have that number, simply divide the total wall SF by the bale SF and that will equal the number of bales you need. You can also add 10% for waste just to be sure. It’s FAR better to end up with a few extra bales than to be a few bales short during the build.

Approximate Square Footages Based on Standard Bale Sizes:2-String Bale Laid Flat = 3.5 – 4.0 SF (depends on if bales are 14″ or 16″ tall)

3-String Bale Laid Flat = 4.5 SF

2-String Bale On Edge = 4.5 SF

3-String Bale On Edge = 6.7 SF

In your last response you spoke about orientation of the bales (flat/edge) and I was curious if there is any pro/con of one over the other?

Does flat vs edge have any effect on say R value or structural integrity…or just personal preference/end product visual

Thank you!

Hi Kelly, The question regarding which bale orientation to stack your straw bale walls is one of great debate. Andrew teaches stacking the bales flat, and I have been building with bales on edge for nearly twenty years. The choice comes down to the design philosophy and personal choice of who is designing and building the wall. There are pros and cons to both methods. The blog post titled 10 Reasons To Never Stack Your Bales On Edge offers an excellent discussion in the comments section. I think you’ll find that there is no right or wrong way, just different ways.

This article was written many years ago, and I bet if you ask Andrew today, he has softened on his perspective of bales on edge. You can be sure that there will be more information about stacking bales on edge on our website in the future. I’m a fan.