Tread and Riser, FBC or FBRC?

[RICHARD TAN]

Hi Jerry,

I know what FBC (Florida Building Code) mean but lately the builder is referencing to FBRC requirement. What is FBRC? I have noted on the reported the tread was 9 3/4" up to 10" tread is too small and is Life and Safety hazard! but the builder has stated that it did meet FBRC requirement and the reference to §1007.3.1 is incorrect.

IRC
R311.5.3.2 Tread depth. The minimum tread depth, exclusive of nosing shall be 9 inches (254 mm).

FBC 2001
§1007.3.1 Risers shall be a maximum height of 7 in. (17.8 cm) and a minimum height of 4 in. (10.2 cm). Treads shall be a minimum of 11 in.

Which reference is right?

[Jerry Peck - Codeman]

Hi Richard,

The builder probably means FBCR, or FBC-R, both of which mean the Florida Building Code, Residential. In the Florida Building Code series of codes, there is the FBC-B which is Florida Building Code, Building, then there is the is the FBC-R which is the Residential code, then the other codes are actually FBC-P (Florida Building Code, Plumbing), FBC-M (Mechanical), etc.

FBC really only means "The Florida Building Code" series of codes. Many use it when referring to the Building code of the Florida Building Code series of codes, which makes sense but is technically incorrect.

Likewise, the Florida Building Code, Plumbing is usually referred to as the FPC, which is also technically incorrect. The same applies to FMC (Mechanical code), FFGC (Fuel Gas code), etc.

I have noted on the reported the tread was 9 3/4" up to 10" tread is too small

the builder has stated that it did meet FBRC requirement and the reference to §1007.3.1 is incorrect

The reference you gave of 1007.3.1 is incorrect as that is from the 2001 FBC, which was replaced with the 2004 FBC series of codes in December 2005 if I remember correctly.

His reference, and yours, should have been to the 2004 FBC, Residential as this: (underlining and bold are mine)
- R311.5.3 Stair treads and risers.
- - R311.5.3.1 Riser height.
- - - The maximum riser height shall be 7¾ 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).
- - R311.5.3.2 Tread depth.
- - - The minimum tread depth, exclusive of nosing, shall be not less than 9 inches (229 mm). Treads and risers of stairs shall be permitted to be so proportioned that the sum of two risers and a tread, exclusive of projection of nosing, is not less than 24 inches (610 mm) nor more than 25 inches (635 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). Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured as above at a point 12 inches (305) mm from the side where the treads are narrower.Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12 inch (305 mm) walk line shall not exceed the smallest by more than 3/8 inch (9.5 mm).
- - R311.5.3.3 Profile.
- - - The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14.3 mm). Every tread less than 10 inches (254 mm) wide shall have a nosing or effective projection of approximately 1 inch (25 mm) over the level immediately below that tread. Beveling of nosing shall not exceed ½ inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch diameter (102 mm) sphere.
- - - - Exceptions:
- - - - - 1. A nosing is not required where the tread depth is a minimum of 11 inches (279 mm).
- - - - - 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches (762 mm) or less.

Attached is an annotated photo showing where riser heights and tread depths are measured.

Going back to your measurement and making some presumptions of those measurements:

I have noted on the reported the tread was 9 3/4" up to 10"

Presuming your measurement included the nosing (as this is a common way people measure treads), and the required nosing is the required 1 inch, that makes "the tread depth" itself only 8-3/4 inches to 9 inches, which is insufficient to meet the code.

Additionally, if the treads varied between 8-3/4 inches and 9 inches, the tread depth itself is insufficient as 9 inches is the minimum required tread depth.

Then there is the two risers plus one tread equals between 24 and 25 requirement which needs to be met in addition to the other tread and riser requirements. Thus, if the tread is 9 inches, then the riser heights much be between 7-1/2 inches and 8 inches high except that the maximum allowable riser height is 7-3/4 inches.

Thus, with a 9 inch tread the riser height would need to be between 7-1/2 inches and 7-3/4 inches in height for that to meet code.

Regardless, if you measured as I suspect you measured, that stairway *DOES NOT MEET* the requirements of the 2004 FBC-Residential.

Do you have any additional information you can provide as how you measured tread depth, if there was a nosing, the amount of nosing, and the riser heights? With that information I could provide a more detailed response of exactly what does not meet code, other than as it stand now with my presumptions that the tread depth is insufficient.

[RICHARD TAN]

Hi Jerry,

From the tile floor to the first tread is 5 5/8", then from the first tread to the second tread is 7 1/2", Tread 10" = 23 1/8. Did not meet the 24"- 25". and not more than 3/8" difference between tread.

[Jerry Peck - Codeman]

Hi Richard,

From the tile floor to the first tread is 5 5/8", then from the first tread to the second tread is 7 1/2", Tread 10" = 23 1/8. Did not meet the 24"- 25". and not more than 3/8" difference between tread.

Yikes! That one is really bad.

Usually what happens when the first (bottom) riser is off is that the stair installer did not allow for the finish floor thickness, but that usually means the risers are 7-3/4 inches except the first one is only maybe 6-1/2 inches (for natural stone flooring or 3/4 inch wood on 3/4 inch plywood nailed to the slab) ... but 5-5/8 inches?

What is the finish flooring and how thick is it?

How are the rest of the treads - are they close to that 7-1/2 inches?

Usually the problem riser heights are at: the first (bottom) riser; the last (top) riser; then wherever there is a landing. Typically the other risers are all real close, with the cause of the aforementioned risers being off was that no one allowed for floor or landing thicknesses. That is a VERY COMMON problem.

How about the treads? You said the tread was 10 inches, is that including or excluding the nosing, if including the nosing, then that two risers plus one tread was only 22+/- instead of 24-25.

Depending on what the actually riser heights are at each riser, it may be possible to add enough height to the lowest riser, cutting back at each next riser up, keeping all risers within 3/8 inch of highest-to-lowest risers.

An example which I've had done would be to add 1-1/2 inches to the lowest riser to make that riser 5-5/8 + 1-1/2 = 7-1/8 inches, then add 1-3/8 inches to the next riser's height, reducing the additional height by 1/8 inch (in this example) until only 1/8 inch was added, then nothing at the landing - all depending on the number of risers in the total stairway and flight of stairs. Does not take a lot to work out the math which will correct it, but it does take a skilled stair person to make the numbers work on the actual stair - but I can attest to the fact that *it can be done and be done where the stair comes out correctly*.

One stair which was corrected that way came out right at the maximum allowable 3/8 inch riser height variation, while another stair corrected that way came out almost exactly dead on with all risers being the same exact height, yet another stair came out ... well ... let us just say that the person who built the stair in the first place tried to correct it, and not knowing how to build it in the first place meant they ended up really screwing that stairway up and it had to be ripped out and rebuilt from scratch.

In another case the risers were so far off in so many places that even the math never came out right and that stair had to be ripped out and rebuilt.

*Can* it be done? Absolutely.

*Can that builder* accomplish it? I have no idea, but it is worth them putting their best craftsmen on it and trying it.

[RICHARD TAN]

Hi Jerry,

No nosing, carpet on top.

[Jerry Peck - Codeman]

Hi Richard,

You reported that some treads were only 9-3/4 inches, all those treads less than 10 inches (even if only one tread is less than 10 inches) are REQUIRED to have a nosing, and once one tread has a nosing all need to be the same so all would be required to have a nosing.

Sounds like the stair builder/contractor really screwed that stairway up big time.

[Jerry Peck - Codeman]

Hi Richard,

You reported that some treads were only 9-3/4 inches, all those treads less than 10 inches (even if only one tread is less than 10 inches) are REQUIRED to have a nosing, and once one tread has a nosing all need to be the same so all would be required to have a nosing.

Sounds like the stair builder/contractor really screwed that stairway up big time.