Here is a response to a student doing a case study of straw bale homes in North Carolina. He had a good question about securing bales to foundations in an existing structure in Alabama. I think the details of the connection are worth mentioning here as well.
I am glad to see that you have chosen such a cool topic for your case study! Perhaps the most important distinction to make is that the homes are made with straw bales, not hay bales. Hay would be a food source for many critters and would also run the risk of fire because of the higher moisture contents within hay bales. Straw on the other hand has no food value and is extremely dry, typically around 8% moisture content during installation.
The old style of construction has changed significantly in recent years so how the bales were attached to the foundation in the building you are studying is hard to say. In today’s homes, we use a system that bolts 4×4 sills to the foundation. Those sills are place on the interior and exterior faces of the bales so each bale is held up n both sides at the bearing points.
The space between the 4x4s is filled with gravel and/or rigid insulation. 20 penny nails are then driven into the sills at 4″ on center staggered from one side of the sill to the other (both sills are nailed and treated as separate entities when measuring the layout of the nails). The nails are only driven in until firmly secured in the sills and about 2″- 3″ of nail is still exposed above the sills. The bales are then placed on the nails and held tightly in place by the “grab” of the nails. That is the easiest and most effective way of connecting to the foundation.