I've got a interior stairwell with 20 steps of 7 1/2" rise on wood treads, except for the bottom step that's a concrete tread 6 1/2" up from a slab. The top of the stairwell features a pocket door with more or less a 3/8" sill (so technically that top step is 7 7/8"). Despite the somewhat uneven stringer cadence, it has been fine for many years.
But now we want to add a basement subfloor (dricore venting style) which adds at the very least 7/8". What can we do to even back up the stair treads? How bad is a short bottom step (I know it's better than a tall bottom step)? How thick a subfloor + carpet could be tolerated on the slab?
The current stair is carpeted, and we'll probably put back carpet. USA based California, home era 1920's.
This one shows the best example of the effect I was trying to explain. I do not have a shot that shows how the handrail goes past the ceiling, but with a little imagination you could picture what the rail would have to do if the stairs were much wider at the bottom.
Best Answer
The key is to eliminate any variation over about 1/8" to prevent tripping. You can change the rise gradually and most folks won't notice it.
Sounds like you'll have about a 2" discrepancy to deal with. I'd remove 6-10 treads and start adding wood strips to the stringers to bring the bottom rise to say 7", then add 1/8" to each subsequent rise until you're at 7-1/2". Be sure to account for finished flooring.
If you want to better handle the tall top rise, remove all treads and work up as I described to its height in 1/8" increments.
Use construction adhesive and small nails or screws for all strips, and glue and 3" screws for the treads to prevent noise.