We have replaced our carpet with laminate, but when the carpet was removed from the stairs there is very rough plywood in place, with 36" treads that do not reach the walls... 1/4 to 1/2 " gap on each side, and two triangular landing treads as well. We have decided NOT to put laminate on stairs, but need advice as to how best to cope with the circumstances, as most replacement treads come with a bullnose, making it difficult to envision how to run molding down the sides to come around the bullnose.

Stairs where built from bottom up.

Solution#1 Best way
Have a stair company install professional stairs.

Solution #2
Measure height of each riser.The measurement should be the same for all.

Remove plywood treads and risers starting at top and working to bottom. Do not remove supports for treads and risers.

Starting at bottom, glue and nail new riser to supports. Cut 1/16'' less than opening.

Glue and nail tread to supports and riser. Allow 1'' from face of riser to bullnose. Cut read 1/16'' less than opening.

Mount nailer on tread in line with next riser support.

Build stairs in this manner to top.

Save pie shaped plywood treads to use as templets.

Solution #3 The worst
Cut plywood treads flush with existing risers

Install new risers and treads 1/16''less than opening

Top step will be 1 5/8'' higher then floor. This will create a tripping edge.

Bottom step to floor will be 1 5/8'' higher. Also a tripping condition

I would personally go for option #1

Good luck

Chuck

Cut a fake stringer as shown below. Remove existing plywood treads. Cover existing risers with 1/4 plywood of same species of wood as treads will be. Use construction adhesive to secure riser covers and nail at very end only.
Install fake stringer. Install new wood treads to fit between fake stringers. Cut to fit tight. Note that you appear to have 3/4 plywood treads currently. Most purchased tread material is 1" thick. That will make 1/4 difference at top. You may be able to mitigate that by lowering top tread by 1/4" and second tread from top by 1/8". Note also that one present tread appears to be 1/2". You will have to install blocking to the wall on the right hand side where stairs make turn. The risers will not meet at that point.

After removing existing treads you will probably have to install nailing block to esisting stringers so that you have something to nail new treads to after installing fake stringer.

Fake stringer can be made from plywood of same species, backed by filler strips and veniered on top edge if run is 8' or less.