This whole thing reminds me of the way houses were built on the Upper Great Plains circa 1880-1920.
Since there wasn't hardly any lumber, houses were first made of sod bricks.
And then as one prospered, one could afford to have lumber shipped, to built a wood house.
This was usually done by building it attached to the old sod house.
All the nice stuff was then moved into the newer part of the house, while the sod part was used only for storage and somesuch.
A sod-wood combination would last maybe about ten, twelve, years before the sod disintegrated back into the soil. And in the meantime, more was being added to the newer, the wood, part of the house.
One wonders if the old DU's meant to be the sod house, and the new DU the wood house.