Hi. I am installing hardwood stairs to replace carpets. Underlying treads and risers are 3/4" plywood so planning on installing with glue/nails over the plywood. However, the plywood risers are not perpendicular to the treads (angled inward from top to bottom) so the overlay of the new hardwood risers leaves a gap from the front edge of the existing tread. If I install nosing over that, there would be a 1/4 -1/2 inch gap between the top of the existing plywood tread and the inside of the new riser. The gap would not be visible as it would be covered by the new nosing but I am concerned about structural integrity of the stairs without the new riser being completely flush to the underlying plywood riser from bottom to top. I am considering using a few shims across the stair to fill the gap, or I guess I could use a belt sander to make the existing plywood riser flat from top to bottom. Any advice on whether it is ok to install without dealing with the gap, or if I need to address it, best method to do so? Trying to avoid completely replacing the existing plywood risers and treads if I can. Thanks in advance for any advice.

the plywood is your structure..you are just overlaying..if the plywood is structurally sound, your overlay if just cosmetic.

Thanks James. I didn't mention that I am using 2 1/2 inch tongue and grove planks for risers and treads. The top plank on the riser would therefore only have glue and face nail attachment to the existing plywood tread on about the bottom 1/2 of the width of the plank, but then also be secured to the new nosing. Do I need to worry about the 2 planks used on the riser buckling once it is stepped on? Picture here: http://www.flickr.com/photos/30798580@N03/

No I dot believe you have any worries..but if it makes you feel better..laminate the front of the risers with some shakes..then install your strips..

between adhesives and nails its going nowhere.

Thanks much for the advice.

More than likely you will be ripping the top board of the riser. Rip it on the angle degree you need, to make it flat with the tread.

Or fur the bottom of the riser out so it is a 90º and face it with thin plywood, to glue and blind nail your flooring to.