A simple tool takes the guess work — and a lot of the brain work — out of making safe comfortable stairs.
Every time I’m asked to bid or to build a set of stairs, I unroll the plans, look at the details, and shake my head. Architects rarely include and often they don’t even have the basic information I need, the few specifications that allow me to build a staircase that will meet the stringent requirements of building code in my area.
Before I can layout a set of stairs, I need to know the exact thickness of the finish floors, including the floors at the top of the stairs, at the bottom of the stairs, as well as on any intermediate landings. I also need to know the run of the stairs—exactly where the architect wants the stairs to start on the first floor and finish on the second, third, fourth, or fifth. And finally, I need to know the exact thickness of the finish treads. Once I have that information, I can make a story pole that allows me to build a stair with confidence that’s dead accurate, never once stopping to scratch my head over the calculations.
A story pole: Every measurement on a stick
Before I describe the layout process, I can’t stress enough the importance for every step of a staircase to be exactly the same height; a 1/4-in. difference between steps can be dangerous if not fatal. And with all the factors that go into a set of stairs, it’s very easy to make a mistake in layout or construction, which can throw off the consistency of the rises.
As with all my finish carpentry, I follow two rules that make my staircases accurate and right: First, I design and layout the work completely before I build it. Second, I start with the finish and work back to the rough.
For complicated projects, a fullscale drawing or loft always works best. (I never depend on the architects 1/4-in. scale drawing—It’s not nearly accurate enough for stair building). But for most of the stairs I build, I just make a story pole, a crucial tool for precision stair building.
A story pole is basically a full-size elevation drawing shrunk down into one dimension—a line, in this case a 1×4 stick. I start by making field measurements, the first of which is the floor-to-floor height from where the stair will start—about the middle of the first riser location—to where the stair will end—about the middle of the top riser.
Measuring the floor-to-distance
Taking an accurate floor-to-floor height measurement is critical. On rare occasions, as with a spiral stair, these points might be plumb above each other, but in most cases, there can be 10 or 12 feet of horizontal distance between the starting point and the ending point of a staircase. We all know that floors aren’t level. In 10 or 12 feet, I’ve seen floors rise or fall more than an inch, especially if one end is in the middle of a floor and the other is at a bearing wall.
[A story pole is basically a full-size elevation drawing shrunk down into one dimension—a line, in this case a 1×4 stick. See photo, RIGHT.]
To measure the floor-to-floor height accurately, most folks use either a long spirit level or a water level, but a laser level is the fastest and most accurate way to
find the difference in elevation between two points that are separated by a large horizontal distance.
For all my stair work, I use a Stabila Plumb-Bob Line Laser. This single tool emits a horizontal line that’s easy to see for making measurements like these. (It’s a pulsing laser as well, so even if I can’t see the line, I can use a receiver to ‘hear’ the line). The laser also has plumb dots which are invaluable for setting newel posts, balusters, etc.
[Measurements in motion. In the animated drawing above, we zoom in on three trouble areas for stair builders.]
I set up the laser so that the horizontal laser line falls at a convenient height between floors, and so that the laser line passes both over the bottom tread location as well as under the top tread location. I measure from the rough floor down to the laser line at the top-riser location, and from the rough floor up to the laser line at the bottom riser location. Adding the two dimensions together gives me the rough floor-to-floor dimension. I mark that number in my ever-present notebook. While the laser is set up, I also mark the laser line on the studs where the stair is going. More on that later.
Add the upper finished floor, subtract the lower
Before I can layout the stairs or my story pole, I need to know the thickness of the finish floors, especially if the lower floor thickness is different than the upper floor, which is often the case. For example, the second floor might have 3/4-in. tongue-and-groove hardwood over the subfloor. I add whatever the thickness is to the rough floor-to-floor dimension I found earlier.
Frequently, the stairs I’m asked to build land on a lower floor that will have a subfloor for hydronic heat, plus 3/4-in. hardwood, or thick 1 1/4-in. tile, or even 2-in. stone! That total dimension–the thickness of any subfloor plus the finished floor at the bottom of the stair–must be subtracted from the floor-to-floor dimension. Adding the thickness of the upper floor and subtracting the thickness of the lower floor from the rough floor-to-floor dimension gives me the total height of the stairs, finished floor to finished floor.
Modern carpenters use calculators
As you can see, there’s a lot of fractional math involved in building stairs, which means lots of room for arithmetic errors—errors that must be avoided if you want the job to run smoothly and the stair to come out in the most pleasing manner. To minimize math errors, I always use a Construction Master foot/inch calculator for all my stair computations. Not only does a foot/inch calculator make it a lot easier to add, subtract, multiply and divide fractions of an inch, but it eliminates cumulative error. More on
that in a minute.
For the example we’ll be using in this article, I measured for a stair in my shop, going from the shop floor up to the loft. The floor thickness and change of direction of a landing adds other layout challenges, so I decided to plan for an intermediate landing with a right angle turn. I also decided that the loft will get 3/4-in. hardwood flooring, (typical for a second floor), and the main shop will have 3/4-in. hardwood installed over 1/2-in. hydronic subfloor.
The measurement up to the laser from where the first tread lands on the shop floor is 45 5/16 in. The measurement down to the laser line from the loft is 54 3/8 in. By adding the two together in the calculator, we know the rough floor-to-floor measurement is 99 11/16 in. [See Fig. 1, LEFT]
Next we add 3/4 in. for the finished loft floor, which gives us 100 7/16 in. Finally, we subtract 1 1/4 in. for the finished shop floor. That means the finished floor-to-floor distance is 99 3/16 in. [See Fig. 2, RIGHT] If I were measuring a jobsite, I’d write that number down in my Job Book.
CALCULATING THE RISES
The next step is determining the distance in height between the finish treads, also called the net rise. To get this number, I usually divide the finish floor-to-floor dimension by 7-1/2 in., which is a good average rise for a residential stair. Unless the floor-to-floor figure is exactly divisible by 7 1/2—and I’ve never worked on one that has been—there will be a remainder. To get the number of rises for this example, I divide 99 3/16 in. by 7 1/2 in. The result is 13.225. I’m obviously not going to make 13 normal risers with a short one at the top. The point of the initial calculation is finding the precise number of risers needed for the stair. In this case, I round 13.225 down to the nearest whole number, 13.
Dividing the finished floor-to-floor height, 99 3/16 in. by 13 gives us 7-5/8 in. rounded off by the calculator to the nearest 1/16th. (By pressing the ‘Inch’ key on the calculator, you can see what I mean. The decimal fraction for 7 5/8 is 7.625, but the decimal fraction for this calculation is really 7.629808. That’s the fraction the calculator will be working with, while giving me the nearest number in a more friendly format).
Press the ‘Inch’ key once more to return to fractional inches. Then press ‘Memory +’ [circled button on left] so the calculator remembers that fraction.
Anyone who has ever laid out a stair with a framing square and gauge stops, or used a gauge block to layout repetitive elements such as dentil blocks or wainscoting stiles, has probably experienced cumulative error. If you lay out a stair stringer by stepping off the risers with a framing square, no matter how carefully you set your stops, you could be off by more than 1/2 in. when you get to the last rise. That much of a difference is not acceptable and won’t pass close inspection or code.
By using the calculator’s memory function, I avoid cumulative errors that occur when extremely small fractions, maybe 1/64 or 1/32 in. add up in a repetitive calculation. By default, Construction Master Calculators are programmed to round off small decimal fractions to the nearest 1/16 in. (You can change the programming if you want to work to 1/32 in. but it’s not necessary). If the calculator comes up with a figure that slightly smaller than 3/32, it will round the number displayed down to 1/16 in., while it continues to work with the finer decimal fraction.
Making the story pole
I like to use a clean, straight 1×2 or 1×4 for making story poles, one that’s a little longer than the floor-to-floor distance. I set the pole on horses or on a bench, and hook my tape at one end. (For the sake of precision and clarity, I always hook my tape measure on the bottom of the pole).
First I mark off the height of the finish floor at the bottom of the stair, which includes hydronic heating and the hardwood flooring.
With the tape still hooked, I run up to the other end and mark the rough floor-to-floor distance, and then add on the thickness of the upper finish floor.
Next, I mark the tops of the finish treads. I find their locations with the calculator. [See Fig. 4, LEFT and Fig. 5, RIGHT]
That means for your first finish tread location, you must add the thickness of the hydronic subfloor and finish flooring. My last keystroke ‘Memory +’ entered the decimal fraction into the calculator’s memory.
Next I add the thickness of the lower flooring. By using the keystrokes below, the calculator automatically adds that amount to the tread height, putting the first tread at 8 7/8 in.
That simple sum is a critical first step in laying out the story pole.
Locating the tops of all the remaining treads is now extremely easy. We just asked the calculator to add the tread-to-tread rise to the first floor thickness. Now the calculator is ready to give us the rest of the tread heights with the lower flooring already factored in.
As you climb up the story pole, marking the finish top of each tread, you’ll notice that the sixth tread lays out at 47 in. But the calculator puts the seventh tread at 54 11/16 in., not at 54 5/8 in.! As I explained earlier, the calculator isn’t adding 7 5/8 each time, it’s adding the decimal fraction, 7.629808. When the “leftover” fraction in the calculator’s memory hits 1/16 in., the calculator automatically adds that amount to the next result.
[Click, watch, learn. In this short video clip the author takes us through story pole layout with a few nifty tips.]
After marking the tops of every finish tread, I’m ready to work back to the rough dimensions. Remember, always start with the finish and work back to the rough. I detail each tread down the thickness of the finish tread, and down again the thickness of the subtreads. The lowest line at each tread is the height of the cut on the stringer for that tread. I pay special attention as I detail the thickness of the finish materials and subfloor at any intermediate landings, as well as at the top and bottom of the stair. These are places where the rough rise can vary because the thickness of the finished flooring might be different than at the finish treads.
For example, the treads might be detailed down 1 1/16 in. for a 5/4 tread. But the intermediate landing, which gets 3/4-in. hardwood, is detailed down only 3/4 in. The landing will get a rabbeted nosing so that it looks like it’s 1 1/16-in. thick, but the flooring is actually only 3/4-in. thick.
When all finish and rough stair parts are located and labeled on the story pole, I stand it up on the subfloor at the bottom tread location, and mark the location of the laser line. The story pole is then complete.
Now I have a full-scale elevation of the stair layout, all in the compact package of a 1×4. I can take the dimensions of the rough common risers, as well as those of the top, bottom and landing risers directly from it. I can also line up the laser line on the story pole with the laser marks I made on the wall studs, and I can transfer the heights of frame elements right from the story pole to the house frame. In the end the story pole will help me get all the finish risers the correct height.
According to the code in my area, the difference between tread heights can’t exceed 3/16 in. If you care about craftsmanship, and want to leave behind exemplary work, challenge yourself. Try to build your stairs so that the difference between risers is 1/8 in. or less. And at the same time you’ll avoid unpleasant visits from the building inspector.
Jed Dixon designs, builds, and restores stairs and stair parts in historic New England homes. A sometime-Luddite*, Jed uses power tools in his shop to make everything from treads to turned balusters to hand-carved volutes and railings. And while he orders the occaisional custom part from a local CNC operator, and he’d never part with his Macintosh, I-Phone, or Ipod. Jed and his wife Helen raised their three kids in a 19th century farm house on their rural Rhode Island farm. Kip, their working sheep dog, lets visitors know that stair building may be Jed’s profession, but the farm is his passion.
* A follower of Ned Ludd, a mythical revolutionary said to have destroyed two knitting machines in the late 18th century which inspired a rebellion by early 19th century skilled craftsmen against the mechanized world of the industrial revolution.