All the pictures I've seen of modified box beam strawbale houses used solid plywood to created the box beam posts. This seemed like a big waste of wood since the plywood was being used where it wasn't structurally put to full use.
So I came up with the idea of using small diagonal pieces as seen above.
The advantages are:
The disadvantages are:
- Compared to using solid plywood, uses less plywood.
- Smaller scraps can be used instead of full sheets. Including lots of wood which would just be sent to the landfill or burned.
- The posts can be made to any width without having to worry about splitting a full sheet of plywood evenly (e.g. cutting a 4'x8' sheet for 18" wide posts creates a lot of waste).
- The straw insulation can be stuffed in later into the posts, when the roof is on. This decreases the chance of it getting wet and allows you to stuff the straw very tightly in the post (which is hard to do when stuffing the straw at the time you build the posts).
To help figure out all the angles, the amount of plywood/OSB needed, etc. I've created a little spreadsheet to help calculate this stuff. Here it is. Actually in the end when it came time to build the posts, I pretty much ignored the spreadsheet! It is not too hard to just lay a piece of wood on the post and just mark the angles. And then cut 20 pieces the same!
- It takes longer to build the posts.
- The strength of the post depends more on the quality of construction, as compared to using solid plywood (which is pretty idiot-proof).
Another suggestion: if your posts are going 2 stories high then don't build them all in one piece. Instead, build them in 2 pieces and add the 2nd floor posts after putting up the 1st floor posts. The reason: the posts are much easier to handle and also much easier to get aligned vertically (i.e. straight) since you can correct when adding the 2nd floor posts.
Anyhow... I just wanted to share this idea - maybe this will spark some other ideas.