My house did not originally have a basement. Some time in the 70’s the then-owners excavated under the foundation, added stairs down the back porch and created a basement.
The back porch is also an add-on. It has a cinderblock foundation with no insulation.
It gets cold under there, so I thought I’d fix it because “under there” is actually inside the house–in my laundry/mud room.
I lined the perimeter with straw bales.
They didn’t reach all the way up the cinderblock, so I might have to get in there and adjust–or add another layer if I can squeeze one in–but I think it’s helping.