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Looking for Local Input on Adoptions

tbz

Silver Member
Joined
Sep 10, 2010
Messages
1,250
Location
PA/NJ - Borderlands
Afternoon All,

Been working on researching on stair tread risers and tread depth adoptions vs adoptions with modifications.

I am working on putting a list together on what jurisdictions are adopting the IRC 7.75" Riser x 10" Tread standard that is published in the IRC and how many modify the the model code on adoption like Pennsylvania does, 8.25" Riser by 9" Tread.

I was hoping to get a little feedback from those here on the forum as to the area/jurisdiction and what adoption you are following.

Just looking for feed back on what your area is following:
  • Adopted Model IRC: 7.75" Risers x 10" Tread
  • Modified IRC on Adoption: 8.25" Riser x 9" Tread
  • Modified Other and List
Thanks in advance

Regards - Tom
 
Montana state amendment

(10) Subsection R311.7.5.1, Risers, is amended to allow a maximum riser height of 8 1/4 inches.

(11) Subsection R311.7.5.2, Treads, is amended to allow a minimum tread depth of nine inches.
 
The Virginia Residential Code (amended IRC) is also 8 1/4" R & 9" T. The Virginia Construction Code (amended IBC) also allows 8 1/4" R & 9" T in dwelling units.
 
Back in the day we followed the 18 rule, 6/12 was best for walking gait. What you are allowing I see as a future trip hazard.
 
This is what NM uses:

Section R311.7.5.1 Risers
. The riser height shall be not more than eight inches (203mm). The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than three-eighth inches (9.5 mm). Risers shall be vertical or sloped from the underside of the nosing of the tread above at an angle not more than 30 degrees (0.51 rad) from the vertical. Open risers are permitted provided that the openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below do not permit the passage of a four-inch-diameter (102 mm) sphere. Exceptions: (1) The opening between adjacent treads is not limited on spiral stairways. (2) The riser height of spiral stairways shall be in accordance with Section R311.7.10.1.

G. Section R311.7.5.2 Treads. The tread depth shall be not less than nine inches (229mm). The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread’s leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than three-eighths inch (9.5 mm).
 
None of the AHJ's I have worked for in CO have amended it. Previous state code (NC) amended it as of 2012 to 8 1/4"/9, not sure about now. I think the bigger issue is uniformity. I have two sets of stairs, to two different levels of my deck. One has a 7 1/2" riser, the other is 8 1/4". There is about 15' walking distance between the two sets, nobody trips. But if I had those different heights within a single set I would bet most people would. A few people have noticed the difference in steepness, but it hasn't been a tripping issue. In a perfect world we could all be 7/11 but for residential I see no serious issue.
 
If I remember correctly the old rules of thumb were:
2R + T = 24 to 25
R x T = 72 to 77

For public buildings 7" R & 11" T was ideal inside, and 6" R & 12" T was better practice for outside.

Residential was 8" R & 9" T. This was long before McMansions, back in the day of 1200 SF houses.
 
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