# Stairs - Risers and Treads

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8 1/4" here also and as JJ indicated the headroom height is referenced on the mid-point line between the 2 nosings.

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• 4 months later...

PA uses IRC 2015 with PA UCC (Uniform Construction Code) modifications which per Mr Hood, allows 8.25" max risers. PA also repealed Sprinkler requirements for single family and two family detached dwellings (per the various builder's associations lobby). IRC 2015 allows 7.75" max risers.

When I started in the 70's the rule of thumb for comfortable stairs was 7/11 = 18" (I think) so that a stair with 4" risers would work best with 14" treads. 8" Riser would be most comfortable with 10" treads and so forth. Always made sense.

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I was taught that 2R+T = 25" for best comfort.  Actually a range of 24"-26" is acceptable

• 6" R & 13" T
• 6.5" R & 12" T
• 7" R & 11" T
• 7.5" R & 10" T

This formula pretty much always works.  For metric you would just substitute 600 mm or a range of 575-625 mm

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3 hours ago, Joe_Carrick said:

I was taught that 2R+T = 25" for best comfort.  Actually a range of 24"-26" is acceptable

• 6" R & 13" T
• 6.5" R & 12" T
• 7" R & 11" T
• 7.5" R & 10" T

This formula pretty much always works.  For metric you would just substitute 600 mm or a range of 575-625 mm

You're right, I couldn't remember that formula from school. Thanks

I remember the 7-11 rule and now the alternate formula of Rise + Run = 17.5 from a builder I worked for in 1976. Good stuff, Joe. bB

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This is our stair regulations in Oz.

Table 3.9.1.1 Riser and going dimensions (mm)
 Stair type Riser (R) Going (G) Slope relationship (see Open link in same pageFigure 3.9.1.4 below) (see Open link in same pageFigure 3.9.1.4 below) (2R+G) Max Min Max Min Max Min Stairs (other than spiral) 190 115 355 240 700 550 Spiral 220 140 370 210 680 590
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12 hours ago, glennw said:

This is our stair regulations in Oz.

Table 3.9.1.1 Riser and going dimensions (mm)
 Stair type Riser (R) Going (G) Slope relationship (see Open link in same pageFigure 3.9.1.4 below) (see Open link in same pageFigure 3.9.1.4 below) (2R+G) Max Min Max Min Max Min Stairs (other than spiral) 190 115 355 240 700 550 Spiral 220 140 370 210 680 590

What language is this in?!!!? Oy!! (as much as they attempted to convert us in school back in the '70's or '80's, I could never wrap my head around metric's larger numbers, eg 1"= 25.4 MM or 2.5 CM.). The most I can handle and relate to is that a meter (39.375") is a bit larger than a yard (36") or from the Virginia Slims' cigarette commercials: "Just a silly millimeter longer 101's!" (so a typ. cig is 100 MM or 4").

And of course, our government's attempt back then to convert to metric was a complete failure.-bB

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Brad,

Most metric users don't use cm at all.  It's almost always mm except for very large distances and areas where they use m.

For Architectural mm would be used for distances and m2 for areas.

Once you are familiar with metric it's really pretty easy.  It's just a matter of becoming comfortable with the numbers.  There are no conversion factors to make for various units of measurement.

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Joe,

I was being glib and also justifying why Americans (including myself) were/are resistant to adopting metric, especially for construction. Since an inch = 25.4 MM (2.54 CM), an 8' stud would be 2438.4 MM or 24.384 CM (which I can't wrap my visual head around) for it me would be easier to visualize it physically as approx. 2.5 meters.

I imagine the reverse would be true for those brought up using metric. I can see using it for industrial, machine and product design because of the scale of smaller parts and you don't have to deal with fractions.

But, how do you get your head around a 7" Riser designated as 177.8 MM or a Flr to Flr Dimension of 2720.97 MM (8'-11 1/8")? My dinosaur brain doesn't like going there. Kind of like paying 40 pesos for a cup of java or 382 pesos for a Mr Coffee!

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Brad,

I think you'll find that metric countries generally don't use our dimensions for lumber, etc.

Their sizes are rounded to more even mm and the products are manufactured to those sizes.

Glenn could give you examples of their standard stud and plywood sizes.

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I could see that on Glenn's stair riser chart and obviously, once you become accustomed to something it becomes second nature and I'm sure that the 1/16's, 1/8th increments, 24", 16" centers etc would drive them bonkers. Although, we use decimal feet when doing grades and our engineer's scales on site plans. Fortunately, we drive on the right side of the road and don't pay in pounds and quid for a pound of squid! -Chilly in Philly (actually Reading but it didn't flow).

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2 hours ago, Joe_Carrick said:

Brad,

I think you'll find that metric countries generally don't use our dimensions for lumber, etc.

Their sizes are rounded to more even mm and the products are manufactured to those sizes.

Glenn could give you examples of their standard stud and plywood sizes.

Probably more conducive to modular construction too. Minimum "Going" is 240 MM for normal stairs which is an interesting construction term that I've never heard.

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6 hours ago, Archnot-Boltz said:

I was being glib and also justifying why Americans (including myself) were/are resistant to adopting metric, especially for construction. Since an inch = 25.4 MM (2.54 CM), an 8' stud would be 2438.4 MM or 24.384 CM (which I can't wrap my visual head around) for it me would be easier to visualize it physically as approx. 2.5 meters.

Brad,

You are really making it hard for yourself and looking for reasons (that aren't there) to make it difficult!

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I love stairs. I built these on Thanksgiving Day. (Basement set)
And the second set last Saturday. (First floor set)

three more stairs and the roof to go.

that last one was a CA section exported to AutoCAD. Chief isn’t production-level accurate but I can Calc everything so it’s great for the picture.

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16 hours ago, glennw said:

Brad,

You are really making it hard for yourself and looking for reasons (that aren't there) to make it difficult!

Glenn,

not trying to be difficult at all, just a personal observation and take on metric vs imperial. No argument just the perspective of an older school designer about the conversion from imperial to metric that the United States was never able to completely institute or integrate. When I find a product that has metric dimensions I just have to make mental conversions to imperial dimensions or use my Construction Master Pro. (similar to what a semi-bilingual person might do when speaking his non-native language because he thinks in his native language and has to mentally convert into the 2nd language if not fluent in it). I'm done and sorry for detracting from the topic. BB

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• 4 months later...

Here are the amended codes for IRC rise and run here in Connecticut.

R311.7.5.1 Risers. The maximum riser height shall be 8 ¼ inches. The riser shall be measured vertically between leading edges of adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than ⅜ inch. Risers shall be vertical or sloped from the underside of the nosing of the tread above at an angle not more than 30 degrees from the vertical. Open risers are permitted provided that the opening between treads does not permit the passage of a 4-inch-diameter sphere.

Exceptions: 1. The maximum riser height of existing stairs serving existing unfinished attics or existing unfinished basements being converted to habitable space or replacement stairs where the pitch or slope cannot be reduced because of existing construction shall be 9 inches, measured in accordance with Section R311.7.5.1. 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches or less.

R311.7.5.2 Treads. The minimum tread depth shall be 9 inches. 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 ⅜ inch.

Exception: The minimum tread depth of existing stairs serving existing unfinished attics or existing unfinished basements being converted to habitable space or replacement stairs within existing dwellings shall be 8 inches, measured in accordance with Section R311.7.5.2.

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12 hours ago, MikeCSD said:

Here are the amended codes for IRC rise and run here in Connecticut.

R311.7.5.1 Risers. The maximum riser height shall be 8 ¼ inches. The riser shall be measured vertically between leading edges of adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than ⅜ inch. Risers shall be vertical or sloped from the underside of the nosing of the tread above at an angle not more than 30 degrees from the vertical. Open risers are permitted provided that the opening between treads does not permit the passage of a 4-inch-diameter sphere.

Exceptions: 1. The maximum riser height of existing stairs serving existing unfinished attics or existing unfinished basements being converted to habitable space or replacement stairs where the pitch or slope cannot be reduced because of existing construction shall be 9 inches, measured in accordance with Section R311.7.5.1. 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches or less.

R311.7.5.2 Treads. The minimum tread depth shall be 9 inches. 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 ⅜ inch.

Exception: The minimum tread depth of existing stairs serving existing unfinished attics or existing unfinished basements being converted to habitable space or replacement stairs within existing dwellings shall be 8 inches, measured in accordance with Section R311.7.5.2.

wow I haven't seen those type of codes in years I have a size 15 foot and I couldn't even fit my foot on a minimum tread in your state, remind me not to go there.

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9 minutes ago, DRAWZILLA said:

wow I haven't seen those type of codes in years I have a size 15 foot and I couldn't even fit my foot on a minimum tread in your state, remind me not to go there.

You need one of those Alternating Big-Foot-Tread Stairs!! PA has similar (with 9" nosing to nosing) and 8.25" max risers which allowed builders to keep building older plans. I always use a 10" min. rough cut treat regardless and will only use the 8.25" in an impossible remodel or basement stairs.

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8 1/4" max riser height in NJ

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Residential Stair FBCR 2017

R311.7.1 Width.

Stairways shall be not less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height. Handrails shall not project more than 4-1/2 inches (114 mm) on either side of the stairway and the clear width of the stairway at and below the handrail height, including treads and landings, shall be not less than 31-1/2 inches (787 mm) where a handrail is installed on one side and 27 inches (698 mm) where handrails are provided on both sides.

R311.7.3 Vertical rise.

A flight of stairs shall not have a vertical rise larger than 147 inches (12'-3") (3734 mm) between floor levels or landings.

R311.7.5.1 Risers.

The riser height shall be not more than 7-3/4 inches (196 mm). 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 3/8 inch (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 4-inch-diameter (102 mm) sphere.

R311.7.5.2 Treads.

The tread depth shall be not less than 10 inches (254 mm). 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 3/8 inch (9.5 mm).

Commercial Buildings: FBC 2017

1011.2 Width and capacity.

The required capacity of stairways shall be determined as specified in Section 1005.1, but the minimum width shall be not less than 44 inches (1118 mm). See Section 1009 for accessible means of egress stairways.

Exceptions:

1. Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches (914 mm).

1011.5.2 Riser height and tread depth.

Stair riser heights shall be 7 inches (178 mm) maximum and 4 inches (102 mm) minimum.

1011.8 Vertical rise.

A flight of stairs shall not have a vertical rise greater than 12 feet (3658 mm) between floor levels or landings.

Commercial & Residential

Headroom.

The headroom in stairways shall be not less than 6 feet 8 inches (2032 mm) measured vertically from the sloped line adjoining the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.

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