Stair Tread Support

[Hawk]

I am removing the treads from my basement stairs, which are the typical basement 2x10s at 36" width and carpeted. I will be replacing the 2x10s with 1" Red Oak. The 2x10s are recessed in the stringers for support on each side and no other support. I will be adding a skirtboard to cover the stringers, covering the risers with 1/4" oak plywood then inserting the 1" oak treads. I will use support brackets on each end of the treads, but my concern is support along the treads. If I only use the brackets on the side, will the treads be spongy/bouncy in the middle and eventually warp over time. Should I use support along the back of the treads and if so, what are suggestions? 34" angle brackets? Or would it be better to add 1/2" to 1" support board under the oak treads, though the only problem with that is the treads have a rounded nosing and the support boards would be visible? Suggestions?

[dpb]

"... which are ... 2x10s at 36" width ... recessed in the stringers for support on each side and no other support."

That doesn't meet Code that says cut stringers can be spaced no more than 18" on center.

You need to add the center stringer, then also use a riser board to cover them.

Those existing mortises should be filled to support the new treads with a half-inch solid spacer glued and nailed/screwed into the riser rather than using some external bracket to support the treads.

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[Clare Snyder]

Glue the oak terads to baltic birch ply sized to bring the thickness to the same as the 2X (or the next thicker if necessary and rabbet them down to fit) - this will give you a tread that is stronger and stiffer thanthe original tread. 1 inch oak alone is NOT sufficient. You could keep the plywood back far enough that the rizer covers the face of the plywood. Do not be tempted to just put re-enforcement between the stringers - like cleats.

[Clare Snyder]

Ifthe rizers are structural it makes a big difference - as each tread effectively becomes a truss - with a roughly 7 inch web on each side - one under compression and one under tension (predominantly) at all times. 1/2 or 5/8 inch ply rizers solidly attached both top and bottom will roughly quadrupl? the strength of the tread - and if combined with laminating birch ply the full width of the tread, will provide a VERY strong stair.

[dpb]

By the time go thru all that exercise, may as well just cut the stringer and put it in as should have been in the beginning.