Here's a picture of the lower section stair
stringers that will be connecting to a ledger that's going to be
attached to a wall underneath the lower split landing section.
The actual stair tread is 10 inches and we need to deduct an inch and a
half for the stair ledger width. If we measure the top of the stair
stringer, in the picture above, it should be 8 1/2 inches.
Be careful in a situation like this. If you don't nail the stair ledger
tight to the landing wall or there are any gaps between the top of the
stair stringer and the ledger, you could end up with a stair tread
that's larger than 10 inches.
If this is the case, simply trim off some more wood, where the stair
stringer connects to the ledger, until you have your 10 inches.
Split Level Stair Framing