Max. Stair Riser Height - Builder Question

[JKEdmo]

Good morning,

 

Maybe more of a question directed to builders / framers, but would you have any buildability concerns about a wood framed stair designed w/ maximum allowable riser height?

 

To explain, I designed my stairs on a project with maximum allowable 7-3/4" riser height (California).  Code does permit a 3/8" tolerance between min./max. risers.  Normally, I'd design in some tolerance wiggle room on my floor-to-floor height, but overlooked this and I'd prefer just to leave as designed as I'm pretty far along.

 

Thoughts?

 

Thanks again,

 

Jim

 

[ACADuser]

Here in Florida 7-3/4 max for residential & 7" max for commercial.

The +/- 3/8 will not allow your to exceed 7-3/4", only -3/8.

This is why I avoid 7-3/4  & it is uncomfortable. Also the 10" tread is unconformable as well.

This can be tricky if the finished floors change from your specified thickness.

 

[Joe_Carrick]

There's a formula for comfortable risers/treads:

• 2R+T = 24"-26"

I prefer to keep the risers < 7" and I adjust the treads so that the result of the formula = 25".

Generally my risers will be about 6.75" and the treads will be 11.5" but it really depends on the floor to floor height.

[para-CAD]

From step to step only ⅛” variation is allowed with a max of ⅜” cumulatively over the entire stairway. 

I’ve cut stringers at code limits, but I don’t like to be that close.  And that is a pretty steep stairway to transit.
If you can add a step, passing inspection is much more easy. 
 

https://www.dropbox.com/s/k5zawo1rrm2agfx/RISER MATRIX.pdf?dl=0

 

 

 

[JKEdmo]

46 minutes ago, ACADuser said:

The +/- 3/8 will not allow your to exceed 7-3/4", only -3/8.

 

Yes, I think your code interpretation is correct.  I missed that.  Good to know.

 

31 minutes ago, Joe_Carrick said:

There's a formula for comfortable risers/treads:

• 2R+T = 24"-26"

Thanks!

 

29 minutes ago, para-CAD said:

I’ve cut stringers at code limits, but I don’t like to be that close.

 

Thanks for your realistic "in the field" input!

 

I will revisit this.  You've all convinced me to add a tread.

 

Jim

 

[DRAWZILLA]

i think about the old days when we had 9" risers for residential. Spiral secondary  stairs still have large risers allowable.

[JKEdmo]

41 minutes ago, DRAWZILLA said:

i think about the old days when we had 9" risers for residential. Spiral secondary  stairs still have large risers allowable.

 

I seem to remember 8" treads / 9" risers being allowable in California up until the 90s?  Seems like a distant memory...

[Joe_Carrick]

1 hour ago, DRAWZILLA said:

Spiral secondary  stairs still have large risers allowable.

If that wasn't so it would be difficult to maintain head height clearance.

[GeneDavis]

I try for 7.5 or a little less, and go with tread depth of 10.5.  Using an old standard from memory rise plus run equals 18, I'm right on with that config.

 

Using Joe's 2R + T = 24 to 26, my numbers come to 25.5, not ideal, but OK.

 

When there is plenty of space I like to go down to 7.25 with 10.75 treads.  There is a huge diff in comfort ascending a stair that is 7.25 x 10.75 versus a 7.75 x 10.    

 

The problem with the treads wider than a 10" run, if it's for a hardwood staircase, typically 1" oak treads, is that the stair parts suppliers make the treads for the 10" run size, and not wider.  The builder has to get treads from a local millwork shop custom sized to the 10+ inch run. 

[JKEdmo]

2 hours ago, GeneDavis said:

I try for 7.5 or a little less, and go with tread depth of 10.5.

 

Gene,

 

Thanks for your insight.

 

Jim