Staircase riser - structural?

[aroberts34]

If possible I want to undercut the bottom-most riser of a staircase (to allow continuous laminate flooring planks to be slid underneath). See attached photo, circled in red. However, I don't know if it's a structural part, or whether there is any other reason I shouldn't cut it. Can someone advise?

 

[big-all]

undercut 10mm max all the way round

 

[aroberts34]

Does it look like the wood is supporting anything? If it is, then I'm not sure why cutting 10 mm would be a good idea because it could still crack under the weight of someone. If it isn't, then does it make any difference whether I cut 10 or 100 mm? Just trying to understand your advice! Thanks, Alan.

 

[big-all]

the bottom step in that configuration is always supported at the open end by the floor as its beyond the string
the construction off the curve is likely to be quite blocky with timber glued in for the curve with a minimum 20mm to the to the depth at anyone point the front could also be 1/2" ply or timber
if the riser is properly glued and wedges into the string and under the stair nose a gap under the riser wont matter as the full load will easilly be transferred to each side without the tread dipping

 

[aroberts34]

OK, I think I understand what you're saying. So the riser transfers load to either side, not directly downwards to the floor?

 

[big-all]

if its properly solid
even if you cut right through the front edge providing the gap is flooring plus underlay
by laying underlay on the floor plank upside down on the underlay and use an oscilating saw to cut along the top you will have an exact match slot and material wise give or take underlay compression and blade thickness so even if it wants to sag it wont sag far
but by not cutting right through it will be no more creaky than it is now

 

[aroberts34]

Good explanation, cheers.

 

[tony1851]

When the bottom step is structurally detached from the newel, as in your case, it was usually added as a separate unit, in which case the riser will be supported directly off the floor. So you will need to be careful if cutting any away to slide flooring underneath.