Straw bales can support many different roof systems and are then bearing the weight of the roof we call this system load bearing straw bale walls or the Nebraska Method of building with straw bales. It was back in Nebraska in the late 1800s that straw was first used in the form of bales to build with. We have constructed many homes now and wineries using this method.
The photographs below show the method we have adopted for pure load bearing straw bale walls. We use high tensile fencing wire 2.5 gauge and tie the top plates down with the wire using medium gripples a wire joiner.
You will get a good idea from these photos of this method of building with straw bales. You will need an engineer to design and calculate the load of your roof and width.
We rarely use this method these days prefering our Hybrid Method which we describe on another page.