Insulation

When we renovated the upstairs bath, we found out that there was no insulation in this room. That made me wonder if there might be other rooms that were uninsulated.

When I arrived home on the first day of construction, I was happy to see insulation in the dumpster.

In speaking to the contractor, he said that when the front window casing was removed, they noticed there was no insulation along the edge of the window. I said I wouldn't be surprised if there was no insulation  in the wall.

Out came the hammer and sure enough, there was no insulation. I am dumbfounded. Why insulate 2 exterior walls, but not the third ?