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Looking for Local Input on Adoptions

Discussion in 'Residential Building Codes' started by tbz, Jul 30, 2020.

  1. tbz

    tbz Silver Member

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    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
     
  2. steveray

    steveray Sawhorse

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    8.25 and 9 in CT..And then we have all kinds of mods for existing basements and attics and stuff...
     
  3. mtlogcabin

    mtlogcabin Registered User

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    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.
     
  4. TheCommish

    TheCommish Sawhorse

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    Mass.

    8.25 - 9
     
  5. rogerpa

    rogerpa Silver Member

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    8-1/4 x 9 state wide in Michigan.
     
  6. steveray

    steveray Sawhorse

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    7/11......Jake.....
     
  7. Paul Sweet

    Paul Sweet Sawhorse

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    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.
     
  8. ADAguy

    ADAguy Registered User

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    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.
     
  9. my250r11

    my250r11 Sawhorse

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    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).
     
  10. fatboy

    fatboy Administrator

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    Northern Colorado. As far as I know, nobody has amended the model IRC as it pertains to stairs.
     
    Glenn likes this.
  11. Sifu

    Sifu Gold Member

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    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.
     
  12. ADAguy

    ADAguy Registered User

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    See, 18" rules!
     
  13. Paul Sweet

    Paul Sweet Sawhorse

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    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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