In all my years in the building industry, the two biggest items that I see most people stumble with is math and stairs –generally you either you get it or you don’t. In a way it is funny listening to some custom home contractors compare staircases to black holes as they do nothing but suck time & money. For many production builders they generally don’t have that issue, but simply have a team or “that guy” that does nothing but stairs. Shoot I have even seen companies hand a candidate a 2×12, a framing square, saw & have them cut a stringer to test their skills. (Heh so you say are a Master Carpenter, huh?)
The Back Story:
This last week as part of the SkillsUSA Alabama State Competition, the Carpentry competitors all got to try their hand at it on the last day. While some students did pretty good most of them had some issues. To make it more interesting the plans provided required one to do the math as the answers one would get from a Construction Master® calculator (or just remembering 7/10 or 7/11) would not give them the answers they needed. With this in mind, let’s take a quick look at some of the code basics, the results and tips to get it right the first time.
The Codes (2009 IRC):
- 311.7.1 – Stairways shall be a minimum of 36” wide
- 3126.96.36.199 – Maximum Riser Height is 7 ¾” (max. height difference of 3/8” based on all risers)
- 3188.8.131.52 – Minimum Tread Depth is 10” (max . width difference is 3/8” based on all treads)
- 3184.108.40.206 – Stair tread nosing must extend out ¾” to a maximum of 1 ¼” past front of riser unless the tread is 11” or larger (just like above 3/8” max. discrepancy is allowed)
The reason for the codes? Quite simply it is because it is what feels normal to most individuals, and helps eliminate tripping hazards. For example in a commercial building I worked at, we lost power & the emergency lighting failed to kick on, yet I was able to still head up the stairs without tripping.
The plan & the results:
This is a part of the plan that everyone got – a simple stair stringer with 4 risers & 4 treads. What made it more challenging is if you simply plugged the rise in to a construction calculator, you would end up with 3 treads. If you plugged in the run @ 4’ you would end up with 6 risers. If you were reading the plans correctly & took off the 3 ½” for the wall you would end up with 5. In order to get the correct size you had to take the rise & divide that by 4 (number of risers needed) and then take the run & also divide that by 4 (number of treads required) which ends up being 7 ½” & 11 1/8” (maybe).
Correct number of risers & treads, yet it extends out past the end of the platform & does not appear to be tall enough. (As an FYI, at the end of the day a fresh set of judges is brought in to judge just what was built. This was put in place here to help prevent any perceived favoritism, so I did not pull a tape on any these projects & am just going off the pictures)
Dead on, but is it – just what does that allow 1” for tread really mean?
The first one completed & the only one to nail it to the first day’s work. Interestingly if you look at the bottom step, you might notice that the one riser is an inch or so shorter. So is it right, or is the one above? In the field that question is generally a little more clear cut whereas in a competition, this is one of those items you might want to get clarified when the plans aren’t fully specific.
Ah the dreaded route memorization issue – why steps always have 7” risers & 10” wide treads except for the bottom one & top…
Hmm, another one? Interestingly on this one, neither the bottom nor the top step is trimmed down like the one above
Ok, this one managed to get the height & trimmed the normal spots, however not only was it tacked up contrary to the plans, but they failed to account for the run required as it appears that route memorization reared its ugly head again
Amazingly off the same set of plans we arrived with 6 different stringers and yet they could all still be wrong. When one is in a competition like this you need to make sure that you ask for clarification on items you might not be sure on. Is the 2’ 6” mark for the top of the tread or stringer? Is the bottom step really the bottom step / do we need to remove some for the tread? Is the top step really the top step / do we need to account for any riser thickness? As an FYI, me showing & using these plans is not an issue as all the ones that have been or are used in competition are shared with all the teachers afterwards so they can use them as guides & teaching tools.
Some quick tips & reminders:
- Buy a set of these stair gauge clamps (shown above) as they make layout a snap – just be careful that you don’t cheat the corners
- For exterior stairs, the wood needs to be Pressure Treated with the crown up. One trick we also employ is finding the biggest knot(s) and we adjust our cut layout to make sure as many of them can be cut out.
- Speaking of exterior stairs, don’t forget that the rise is from where the landing will be up to the finish height which in many cases can be difficult if the ground slopes away
- For interior stairs we prefer to use LVL’s due to their strength & wider width. If you use a regular 2×12 – please see above
- In both cases, don’t forget to account for the finish floor heights, tread material & riser finishes. (see picture above)
- Route memorization is bad, especially the 7/10 one – you have to do the math. If you have a Construction Master Calculator it is as easy as typing in your rise & hitting the stair key to get the numbers you need. (as an FYI – they default to 7/10 for the baseline)
- In most cases you really want to shoot for stairs being around 7” tall & 11” wide. In case you have a calculator that is defaulted to 10, there is an easy fix – in my case I simply type in “11”, hit “inch”, followed by “CONV” & hit then the number 9 – now my default tread width it 11 inches instead of 10 until I change it or do a reset to default