The bale is not a product with a spec sheet
Everything on this page hangs off three measured numbers, and the reason they are fields rather than defaults is that they move. Bale length depends on how the baler was set and how the operator was driving; two strings and three strings are different animals; and the same lot will vary an inch or two bale to bale even when the setting never changed. The length is the sensitive one. On a forty foot run at 36 inch bales you get 14 bales a course. At 34 inches you get 15. Over seven courses that is seven bales, and you find out about them on the last course.
So measure. Pull a dozen bales off the actual delivery, measure all three dimensions on each, and use the numbers you get rather than the numbers in a book. If the lot is inconsistent enough that the length spread is more than an inch or so, that is worth knowing before the bales are stacked on site rather than after.
Flat or on edge changes two things at once
A bale laid flat sits on its widest face: the bale width becomes the wall thickness and the bale height becomes the course height. Stood on edge it sits on its long narrow face: the bale height becomes the wall thickness and the bale width becomes the course height. Either way the bale gives its length to the run.
That means the wall face one bale covers is its length times whichever cross-section dimension is vertical. Taking an 18 by 14 inch bale as an example, laid flat one bale covers 36 by 14 inches of wall and gives an 18 inch wall; on edge the same bale covers 36 by 18 inches and gives a 14 inch wall. The on-edge wall covers more face per bale and is thinner. It is one decision, not two, and the calculator prints both so the trade is in front of you rather than in your head. Worth knowing that the layout counts always run the way the face areas say, but the ordered counts occasionally cross once openings are deducted, because a larger bale face takes a larger bite out of the opening area. On a wall with a lot of glazing it is worth reading both numbers rather than assuming.
The count that goes wrong is the deduction
Openings do not remove whole bales cleanly. A window three feet wide sitting in the middle of a course leaves a stub of bale on each side, and those stubs are made by cutting and re-tying a full bale rather than by finding a short one. This page deducts openings in whole-bale equivalents rounded down, which is deliberately the conservative direction, and then puts the cut-down bales into the waste allowance where they belong.
If your wall has a lot of small openings rather than a few large ones, push the waste allowance up. Every opening edge is a custom bale, and the ratio of edge to area gets worse the smaller the opening.
What is not on this page and why
No R-value. Published figures for bale walls vary by orientation, density, render and who measured, and quoting one as fact would be inventing a number. No pinning pattern, no maximum unsupported height, no view on load bearing against infill. Bale construction is outside the prescriptive path in most adopted codes, which means it typically gets permitted through an alternative materials review and often with an engineer stamping the wall. Ask the building department what that path looks like where you are before the bales arrive, not after.
The risk that actually decides whether a bale wall lasts is moisture. Straw that gets wet inside a finished assembly and cannot dry is a rot and mould problem hidden behind render, and the details that prevent it — the overhang, the base above splash, the flashings at every opening, and keeping the bales dry during the build — are the whole discipline of the system. Say that plainly and then get the details from someone who has built them.
Questions people ask
How many bales does a wall take?
It is the wall face divided by the face one bale covers, which is the bale length times whichever cross-section dimension is standing vertically. On the defaults here — a 40 by 8 foot run with three 4 by 5 foot openings, 36 by 18 by 14 inch bales laid flat — the layout is 7 courses of 14, the openings take out 17 bale equivalents, and with an 8 percent allowance the order is 88 bales. Change the bale length by two inches and the per-course count changes.
Is it better to lay bales flat or on edge?
They are different walls and the calculator prints both rather than picking. Where the bale width is the larger of the two cross-section dimensions, standing it on edge covers more wall face per bale, so the layout count drops and the wall comes out thinner, though on a heavily glazed wall the ordered counts can cross over once the openings are deducted. Laid flat gives the thicker wall and takes more bales. Which one suits the building depends on the design, the loads, the render detail and what the engineer and the building department will accept, and none of that is arithmetic.
What R-value does a straw bale wall have?
This page does not say, and you should be careful with any source that does say without stating the conditions. Published test figures differ by orientation, bale density, moisture content, render thickness and test method, and the assembly you build is not the assembly somebody tested. If you have a figure from your own design work, put it into the assembly R-value calculator with the rest of the layers rather than taking a headline number for the wall.
How do I count bales around windows and doors?
Deduct openings in whole-bale equivalents and round down, which is what this page does, then carry the edge bales in the waste allowance. Every opening edge needs a bale cut down and re-tied to fit, so it consumes a full bale and produces an offcut. A wall with many small openings wastes far more than a wall with the same opening area in one big window.
Does this tell me if the wall will stand up?
No. It counts bales, courses, pins and mesh for a wall somebody else designed. Bale walls sit outside the prescriptive code in most places, which usually means an alternative materials review and often a licensed engineer. The section, the reinforcement, the connections at the plate and the height limits come from that process. So does the moisture detailing, which is what actually decides whether the wall survives.