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Stair rise/run question

Posted by CamG (My Page) on
Tue, Nov 13, 12 at 21:51

Hey folks,
Our houseplan's layout really hinges on the dimensions of the stairs, so I want to make sure I'm getting this right.

My builder has said the optimal rise of 7 1/4" and run of 11", and a nosing of 1 1/4". Does the run include the nosing (in other words, for calculation purposes, should the run really be 9 3/4")? The local code requires 10" minimum tread, but is not clear whether that includes nosing or not. In our current stairs, the total tread is 10 1/2", and it seems pretty comfortable.

My other question is whether I'm calculating the total rise correctly: we'll have 8' ceilings on first floor and I believe we are using 9 1/4" i-joists for second floor, meaning the total rise for the stairs will be pretty close to 8'11"--does that sound right?

As I do the math, we can have a stairway with 11" treads (including nosing) and 7 1/8" rise. Does that sound appropriate?

Thanks for any thoughts!


Follow-Up Postings:

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RE: Stair rise/run question

As far as I know, the run does not include the nose projection. I always picture the rise and run as the actual cuts made in the stringers. There are optimums, and there are code minimums and maximums. Usually the maximum rise is 7=3/4, and the minimum run is 10". I think the optimum formula is 2X rise + the run= 25. So 2 X 7-1/8= 14-1/4, leaving 10-3/4 for a run. When calculating the total rise of a stairway, don't forget the finished floor thickness on each floor. It is really critical that each step is exactly the same, so you can't make up an error on the last step.


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RE: Stair rise/run question

Forget the nosing dimension; it is not part of the tread dimension for design purposes. The nosing is added to the tread AFTER all the dimensions of the stair have been determined.

For me the ideal residential stair is R=7.5" and T=10" but that is not the place to start.

Start with the possible riser dimensions since there will usually only be one or two. For an 8-11 floor to floor height 14 risers will give you a riser height of 7.64" and 15 risers will give you a riser height of 7.13". Both are just fine but to me one is a bit too high and one is a bit too low. However, there are no other options unless you change the upper floor height so now determine the tread options for these 2 riser heights.

For comfortable climbing as the riser gets larger the tread should get smaller. Getting too far from the established ratios makes you feel like you must lean more forward or backward (ie, rising too slowly or too quickly) as you climb. The best formulas for determining the best riser to tread ratio are T=20-(4R/3) and R=15-(3T/4). Using the Tread formula for the larger riser option the best tread would be 9.8" and for the smaller riser option the best tread would be 10.5".

Now consider the code (the limitations vary by state so don't make assumptions, read the code!). If the minimum tread is 9", you can ignore it but if it is 10" then the two possible designs are R=7.64"/T=10" and R=7.13/T=10.5".

Now add the nosing. The code max. is 1 1/4" but I always use 1". 1" would give you either an 11" or an 11.5" total tread surface both of which are generous.

Now consider what you like in a stair and how much room there is in the plan. The shorter riser adds almost 18" to the length of the stair. My ideal stair is in the middle of these stair designs but much closer to the taller riser option.

So if you want a slow rising, grander, more generous staircase, chose the shorter riser, otherwise choose the taller one and save some space.


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RE: Stair rise/run question

This is help full.

Here is a link that might be useful: stair calculator


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RE: Stair rise/run question

This is clipping is several years old and not very detailed.


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RE: Stair rise/run question

Unfortunately, the ratio of rise to run used by the online stair calculator is T=24.5-2R instead of T=25-2R (or as usually stated: T+2R=25). This results in a stair that is steeper than you would get using any other "rule of thumb" formula I have ever seen because the tread is always about 1/2 " smaller than it should be. For instance, my favorite stair design of 7.5"/10" would be 7.5"/9.5" using the calculator.

To use the calculator you could find the riser height and then use a more appropriate ratio formula or simply add a half inch to the tread and set the "Ideal Run" to that size and get the stair construction information. In other words, the calculator is a great carpenters layout tool but not a good design tool.


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also

emmachas, I posted that stair chart almost 5 years ago. It's for design not construction so I don't know what additional detail might be added.


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RE: Stair rise/run question

Thanks everyone. Renovator8, you've made me feel a lot better about this--I was worried a rise of 7.64" was to tall. The max for our code is 7 3/4".

I called the building inspectors, and was told that the 10" minimum DOES include stair nosing. So, I can do the 9.8" run as long as I have a nosing that will make the total tread at least 10".

So it looks like we'll go for R=7.64"/T=9.8" plus a 1 or 1 1/4" nosing (depending on the builder, I'm already a huge pain in his @#$%, I won't insist on this). This gives us a really short total run, which is great for the house layout. Thanks again!


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again

On the floor plan show the total number of treads @ the tread size; the carpenter will make the resulting number of risers fit the floor to floor height. The nosing design should be noted separately or shown in a detail to avoid confusion.


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more, then I'll stop

To answer the OP's last question:
The example you described (11" tread including 1.25 nosing and a 7 1/8" riser) would result in a 9.75 tread run which for building code and comfort reasons should be 10.5" + 1.25 = 11.75" or you could use the taller riser and shorter tread option.


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RE: Stair rise/run question

Stair design is always an interesting issue. All of the information above is helpful, in order to understand the building code requirements (as minimums for general safety).

I would just like to raise the issue of "comfort", "safety" and the issue of stairs for folks of different ages and physical conditions.

The older one gets, and the greater the limitations of eyesight and physical dexterity (how easily and how far can one raise one's foot repeatedly when climbing stairs; how far forward one places one's foot when descending stairs, etc) should be as much a design parameter for stairs as the code's minimums and carpenter's old rules of thumbs for stairs.

I find, in retirement, that I much prefer stairs with a wider tread and lower riser. They are much more comfortable to climb and I consider them to be much safer to descend.

Interestingly, the accepted standards for a building's stairs on the interior of the building are generally steeper and shallower than the standards used on the exterior for landscape situations. I've always thought that was for greater convenience and safety in settings where changes in elevation were not so predictable.

Hope this is helpful. For me, I'd exceed the minimum code standards and use a 7"-7.125" riser and a 11.5"-12" tread.

Good luck on your project.


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RE: Stair rise/run question

Renovator8--
I miscommunicated--after your post, I've abandoned the 7 1/8" rise.

We'll do 7.64 rise and 9.8" tread you described (not including nosing). You said that was good assuming no code problems. And although code requires minimum 10" tread, the inspector said they will include the nosing in the 10" measurement. So with a 1" nosing, we will meet code. (I ran these specific dimensions by him and he said it would work.) Unless I'm missing something?


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RE: Stair rise/run question

You misunderstood the inspector's answer. He meant that the 10" dimension is measured horizontally from the tip of one nosing to the tip of the next nosing. If the nosings are the same, that dimension will be the same as the dimension from the face of one riser to the face of the next riser so the total physical size of the tread must be 10" + 1.25" = 11.25".

Please, take my earlier recommendation to not consider the nosing until you have completely finished designing the stairway. The riser and tread run sizes (without the nosing) determine the rate of rise (or angle) of the stair which is what the designer and the building code is concerned with; the nosing has no effect on this safety issue so it is ignored by the code except to limit it to a projection of 1.25" so people don't catch their toes on it.

Here is the usual code wording for treads:
"R311.7.4.2 Tread depth. The minimum tread depth shall be 10 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."

That means nosing to nosing, not riser to nosing. If you measure that way and somehow you get a permit, the stair is likely to be rejected in the field by the inspector and you would have to rebuild it.


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RE: Stair rise/run question

The reason I said 9.8" would be good if allowed by code is that older codes allowed a 9" tread but that was changed to 10" in 2000 when CABO changed it's name to the ICC and published the first International Residential Code (IRC).

In my state the 10" requirement was amended to be 9" so that is why I never assume the limit is 10".

Ask the building inspector what code applies to your project, if there are any amendments, and where you can find all of that information online. Since the tread min. is 10" I would assume you are using the IRC but this is serious business so you must make sure!


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RE: Stair rise/run question

This afternoon I called the building inspector again to figure this out and confirm what code applies. My city adopted the 2009 International Residential Code, which I've been viewing online already. The inspector confirmed specifically that the tread depth 10" minimum is measured from the end of the nosing to the riser. I asked this in several different ways ("if I use a 9" tread, plus a 1" nosing, will that satisfy the 10 in. requirement?" "If I make a 9" cut for the tread on my stringer, and then add another 1" nosing, will that comply?") This is also what my builder said. Our code does not have the section you posted about how to measure tread, and is really silent on this. It does, however, have a section saying that while a 3/4" minimum nosing is required, it is not required if the tread is a minimum of 10". I think that MUST envision that a tread, independent of nosing, might be less than 10" and yet be approved. Either way, it's pretty sloppy drafting if you ask me.

Nevertheless, it really seems our code allows a less than 10" tread if the nosing plus the tread gets to 10". If that's the case, it's best for the floor plan to to use the 7.64" rise and 9.8" run. On the other hand, I'm not terribly comfortable relying on the oral reassurances of an inspector--that would not save me from having to redo it later if that inspector was wrong. And I appreciate virgilcarter's point above about an easier rise/run.

We'll have to play around with it and see how it affects the plan, and see how much risk we're willing to tolerate to gain additional space around the stair. I suspect my builder would think I'm crazy for even questioning this--especially after talking to the inspector. Thanks for all of your help, Renovator8, and forgive my continued beating of this dead horse.

Here is a link that might be useful: Lincoln 2009 Residential Building Codes and Amendments


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RE: Stair rise/run question

Again, I want to suggest that there's another way to consider what's best for stair design, besides code minimums.

Simply take your adult shoe and measure from the back of the heel to the face of the toe. That's the dimension that will be looking for a place to safely land on every tread as one descends the stairs. Descent is the most dangerous direction of travel.

If you figure that one's heel is not going to hit the face of the riser on every step down, then that means the tread must be wide enough for a safe step down each and every time when the foot is some distance from the riser. A 9' or 10" tread may be very dangerous, even thought it's legal!

For those whose shoe size is larger than a size 10 and/or those who just may not always be watching where they step, it may be wise to err on the side of safety with a wider tread, than to scrimp to code minimums for stair treads.

Only a thought! Good luck!


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RE: Stair rise/run question

Point well-taken virgilcater. Regardless of code, 1.25" nosing is not the same as an extra 1.25" of tread.

We hope to have a big family, and a difficult staircase for little legs and feet will cause headaches for years... I'll have to look to see what we can squeeze in there. Then a potentially-code-violating-tread wouldn't keep me up at night either.


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RE: Stair rise/run question

Your jurisdiction adopted the 2009 IRC but then amended it in a way that effectively reduces the minimum tread "run" from 10" to as little as 8.75" which is less than any code I have ever seen or heard of. This is what you would use for an attic stair not the main stair of a house.

But since the minimum code tread run requirement is small it allows you to design a properly proportioned stair. I gave you one (7.64/9.8) that saved 20" in length compared to the only other option (7.2/10.5) but if you are uneasy about the code interpretation just add .2" to the tread and make it 10". Since that only adds 2.6" to the total length of the stair you shouldn't have to "squeeze" it in there. Don't let the framing dictate the stair design. A structure should serve the house design not the other way around.

The nosing is not included in any of these dimensions. For a main stair tread the nosing would be 3/4" to 7/8". A larger nosing would be appropriate for a smaller tread. It's purpose is to allow the edge of the tread to fall forward of the ball of one's foot.


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RE: Stair rise/run question

Your jurisdiction adopted the 2009 IRC but then amended it in a way that effectively reduces the minimum tread "run" from 10" to as little as 8.75" which is less than any code I have ever seen or heard of. This is what you would use for an attic stair not the main stair of a house.

But since the minimum code tread run requirement is small it allows you to design a properly proportioned stair. I gave you one (7.64/9.8) that saved 20" in length compared to the only other option (7.2/10.5) but if you are uneasy about the code interpretation just add .2" to the tread and make it 10". Since that only adds 2.6" to the total length of the stair you shouldn't have to "squeeze" it in there. Don't let the framing dictate the stair design. A structure should serve the house design not the other way around.

The nosing is not included in any of these dimensions. For a main stair tread the nosing would be 3/4" to 7/8". A larger nosing would be appropriate for a smaller tread. It's purpose is to allow the edge of the tread to fall forward of the ball of one's foot.


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RE: Stair rise/run question

Renovator! The stair chart disappeared from my 'clippings'. Had no idea who had so graciously shared it years ago.
Thank you! It has been a valuable tool in planning.


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RE: Stair rise/run question

You're welcome; I put it together because it's a simple design task yet some people find it so difficult.


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RE: Stair rise/run question

This is a link to a visual guide for interpreting stair building code rules. Sorry if it's out of date. PDF.
Casey

Here is a link that might be useful: Visual Stairway Guidelines


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RE: Stair rise/run question

Using the bizarre code amendment in effect for your jurisdiction and assuming the floor to floor height is approximately 108.5" (because the contractor recommended 7.25 risers and he should know the actual total rise), you have a choice of 14 risers @ 7.75" or 15 risers @ 7.23" (but you should ask the contractor for the floor to floor height instead of guessing).

The most comfortable tread "run" for these two options would be 9.67" and 10.36" (the tread gets longer as the riser gets shorter). Adding a 1.25" nosing makes the tread surfaces 10.92" and 11.61" both of which meet the 10" oddball code minimum but I would use a shorter nosing.

So, compared to the above optimal design, the original contractor recommendation of an 11" tread was 5/8" too short if he was using the applicable code definition of "tread" and it was 5/8" too long if he was using the IRC definition of a "tread". Either way his design was not based on any reasonable rise/run ratio.

If you use the 14 riser stair the risers will be between 7.65" and 7.75" which is a bit taller than an ideal stair so you should measure the stairs you are used to climbing and the stairs of your relatives and friends and think about how this riser height would feel. That would give you a tread "run" of 9.67" to 9.77" so with a nosing of 1.25" the tread surface would be 10.92" to 11".

Since the applicable code amendment removed the IRC definition of "tread depth", it is clear that the definition was intentionally left up to the building official so there is little or no risk of someone challenging the stair design later. Just make sure the stair riser and tread are drawn to scale and dimensioned in a blow-up detail on the permit drawings not just noted on the plan.

This is the oldest and most reliable stair design tool I have found. Tread dimensions are without nosings.

Image and video hosting by TinyPic


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RE: Stair rise/run question

I seldom deal with building stairs. But i saw a code some years ago that permitted risers up to 8 1/4 high. The codes apparently have moved in more recent times toward reducing the maximum riser height. While that may make stairs more comfortable to climb and perhaps a bit safer, it can require significant changes to the plans to accommodate the extra floor space required by the increase in the horizontal dimensions of the staircase.


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RE: Stair rise/run question

Ahh, Reno--Graphic Standards! It's been around since forever, and it still works. I've got a vintage 1930's edition, with wonderful details and drawings. I'll have to check to see if the stair diagram is in it. Good post!

Bus driver, you raise a good point about stairs. They do take up room! Stairs alwayes seem to be a balancing act: the steeper the stair, the less room, but the greater the effort to climb and the greater potential danger they pose.

If the space stairs take up was the primary criterion, then we'd all have ship's ladders in our houses!

Another way to think about stairs--rather than being a simple utilitarian necessity--is about their life-long convenience and safety, for a genration of users, young and old. Like the foundation of a house, stairs are one of those items in a home where it pays to think things through, take a wise long-term view and not have to worry later about the short-cuts and few dollars that may have been saved by minimizing the stair design.

It only takes one fall, a broken leg, hip or arm for which no amount of savings in square footage or dollars can compensate. I found out, personally, while carrying one of our cats downstairs in his cat carrier box!

If cost and square footings savings are coloring one's thoughts about stair run and rise, it may be best to compromise elsewhere and cut some square feet out of the Master Bedroom walk-in closet. Or that 3-car garage. There's lots of opportunities to economize in most of today's house plans. Don't do it with the stairs!

Just some thoughts...


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RE: Stair rise/run question

The code in MA has always been 8 1/4" riser and 9" tread and still is by amendment to the 2009 IRC.

The 7 3/4" / 10" limits were introduced in the 1992 CABO 1&2 family Dwelling Code and when CABO changed its name to the ICC that standard continued in all subsequent IRC editions.

The code should be of little concern in designing a comfortable and safe stairway since it doesn't stipulate a rise to run ratio and that information is not difficult to find but one has to be careful to avoid tools like the online stair calculator linked earlier that use an unacceptable ratio.

The old Ramsey & Sleeper written editions of Architectural Graphic Standards are fun to look through but are really more useful for remodeling and restoring older buildings. Of the 11 editions of this book the first one to deal with more modern architectural design issues was the 6th Edition in 1970 because it was the first one written by the AIA.

I would love to own the 11th edition but the hard copy is $250 and the digital version is $650.


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RE: Stair rise/run question

Reno, I agree about the applicability to older buildings, but simply looking at the detailing can be inspiring (at least to retired architects!).

There used to be a student paper-back version of each addition that was much more affordable. Have you checked recently?


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RE: Stair rise/run question

Thanks both of you. I've been taking a tape measure everywhere I go, and the more comfortable steps seem to be the lower rise, deeper tread. I think at this point we will plan to do the lower rise option Renovator gave above. This way, our floor plan will accommodate the longer run in case I'm off on the total rise. We loose space in the entry, but I can live with that. I really appreciate the help, I saw those formulas but never gave it enough thought. I bet most people do not.


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