I recently bought a 3-story townhouse in northern Virginia. I pulled up the carpet on the bottom level (foundation is a slab on grade) and discovered a large crack running along the whole room and into the mechanical closet.
The crack is about 3/8" - 1/2" wide and runs about 16 feet, under the wall at the top of the first photo, into the mechanical room. From there it goes under the furnace, but doesn't appear to continue outside of that room. It starts beyond the bottom of the first photo, at or underneath a gas fireplace. It looks to be up to 3" deep at points, maybe more. I was able to get the ten-dollar bill about halfway into the crack.
Putting a level across the crack produces a slight rocking, maybe a couple degrees, but nothing huge. Each side of the crack appears level on its own.
The townhouse is in a row of 7 townhouses; mine is adjacent to one of the end units. I have no idea how recent the crack is, but the townhouse was built in 1999. I haven't seen any moisture or anything coming up from the crack during recent rains.
How much should I worry about this crack? I plan to get it evaluated by an engineer, but is it something I should do immediately or could I wait a little bit?