I'm replacing the old carpet from my stairs with engineered hardwood flooring. The stairs are 3ft wide. Since the stairs were very, very squeaky, after removing the carpet I removed the old treads and risers and added 2 extra stringers (unfortunately I could only fit 2x10 stringers). So now I have 4 stringers with 1ft spacing between them.
I would love to avoid squeaking in the future, so I was thinking that these 4 stringers would allow me to go with risers that wouldn't touch either of the treads (above or below the riser) - only serve as a backing for the engineered flooring.
Do you see any problems in the risers not supporting the tread?
Thanks a lot,
Nick

Only 2 stringers for a 3 foot wide stair? What were the subtreads under the carpeting? What will the new subtreads be made of? It looks like you may be changing the riser heights....refer to stair building code. If all joints and fastenings are tight there really shouldn't be squeaks. The old subtreads may have been flexing and rubbing to cause the squeaks.

Jimmiem, thanks a lot for your reply,
The old treads were the same material as the new ones - 2x10 D.Fir or SPF. I'm replacing the old ones only because they are really full of cracks, probably due to the tension created by the shrinking stringers.
I kept the old stringers and added 2 more, so this is certainly an overkill. That was the reason for me to think that I can now install risers (subrisers) that wouldn't support the tread - just be used as a backing for 1/4" poplar plywood painted white.
In any case I'm planing on using a lot of glue and good GRK fasteners which will hopefully eliminate squeaks for good.

No reason for the subrisers not to support the subtreads and treads. If all joints are square, tight, glued and screwed you shouldn't any have squeaks. The more support for the subtreads and treads the better.

I would not recommend white or yellow glue.
Use latex sub-floor glue, PL poly-urethane glue or the Bona sausages.
A brittle glue is susceptible to creep failure. You would want a glue that has some flexibility.

Another thought. I would be careful using construction lumber for subtreads. Depending on how it was stored its moisture content is questionable and may be subject to warping, cupping, etc. If you want 1 1/2" thickness how about a couple of layers of 3/4" plywood.