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.