There is no need to have rebar in infill straw bale walls anymore as far as I am concerned. In fact, we have not used it in years, with inspector approvals I might add, even though the Oregon code requires it. Here’s why:
1. Cold steel in the center of the bales is the perfect target for moisture laden air to condense on creating a source for water infiltration into the bales which can and will eventually cause rot. This is not a huge concern because recent research shows that the plaster does a great job of keeping most moisture out of bale walls. Nonetheless, nature is persistent and air leaks can still exist in even the best built bale home.
2. It is a pain in the neck to work with. There is nothing like try to line a 45 pound bale up on the toe ups when you have to lift it 30″ in the air and then slide it down one or two pieces of rebar. In addition, driving rebar into the bales as you stack is difficult and time consuming. Using the mesh, stapled to the frame on one side and sewn through from the other gives you just as much anchoring power as the rebar would, in fact, it creates an even stronger wall than the rebar.
3. The rebar system is attached to the foundation. This means that there is a direct path from the concrete up into the bale walls that cannot be broken. The entire point of adding a moisture barrier to the bottom of the bale walls is to isolate them from the foundation so these to requirements create conflicting results.
4. Rebar stinks at holding the bales securely in place. A far stronger connection for the bales is a series of 20 penny nails driven into the toe ups at 4″ on center (or so). Staggered from one side of the toe up to the other (on both toe ups) they grab the bottom of the bale with teeth that don’t let go. Rebar will slide up and down the bale if you try. It simply does not work well.
Those are the main reasons I don’t use rebar at all, except within my concrete. To me, there are no pros of using rebar and the cons are many. The system I use of nails attached to the toe ups and welded wire mesh attached to the frame and sewn through the wall is much easier and much more durable and quality driven. With this system, you will end up with a tight and strong wall that will be a joy to plaster.