Staircase design (on paper, how precise should I get?)

[Gingerbreadman]

I bought a set of the Big Enchilada plans, and in my spare time I have been trying to work out the details on paper. I have made some minor changes, so that a pretty standard staircase could be used to access the loft/ upper 1/2 story.

I have been designing a staircase in my spare time, but I keep hitting a wall (figuratively). It seems that every time I come up with a new set of numbers, things do no match up. I have been trying to design the stringers, and I am likely being more precise than I need to be, but I am not sure.

My approach is that I cannot be as precise as I need to be with a protractor, so each step should be calculated and measured lengthwise (along the width of a board (2x10, 2x12, etc.). Some trigonometry is involved, which I have been calculating to two digits (using the same web-based calculator-I forgot too much since high school). When I have a diagram that I am happy with, I add the cumulative lengths of the basic board (top and bottom of the board). The closest I have gotten was roughly 1/4" margin over ~96." Unfortunately, I have become dissatisfied with the rise and run that I used, and I am using new numbers, so I am back to the drawing board.

This is a new thing for me, and I do no know if I am being too picky. Are trigonometry calculations out to two digits too demanding on paper? I know that in practice the numbers that I come up with on paper are going to be subject to the accuracy of my tape measure, the thickness of my pencil lead, and the width of my saw blade.

[Don_P]

Measure it with a micrometer, mark it with a crayon, cut it with an axe

I try to get stair sketches dead on before I start. Usually it is simple match and a scaled drawing, basic division and multiplication skills will suffice, trig can provide some nice checks for your work but most of the folks in the field are not math scholars, but yes, to your point accuracy is critical.

[stricsm]

Try using Google Sketchup to draw a three dimensional outline.  You can add dimensions in Sketchup and play with the rise/run/stringer length.  You can also add in the structural details you need.  I've done this for my stairs but haven't built them yet.   I have a ships ladder now and will have to make the opening bigger to fit in a compact staircase.  When I have the exact opening, I'll revisit the Sketchup model and adjust as necessary before I start cutting.  Good luck. 

[JRR]

I like to use the drawings to determine what staircase angle-to-horizontal there will be ... my choice being between 30 -35 degrees, with an absolute maximum of 41 degrees.  The lower angles cost more floorspace of course.  Make sure to observe head-room requirements.  Using a riser range of 6" to 7 1/4" (my choice), the number of steps can also be determined.  I don't try to precisely draw this all in ... but reasonable accuracy is necessary.  This information and sketch is put aside until framing begins.  After the framing is underway, I like to draw the stair case details, full scale and accurately, right on the wall near the stairwell.  First a heavy line is drawn at the chosen angle.  The lowest step is pencilled-in at the calculated rise ... then using a large "divider"... the rest of the inclined line is section off equally ... etc.,etc.  A bit of trial and error may be needed to make the "divider" mark off the steps equally.

A full size, fully detailed layout of the staircase is the result.  And changes/corrections can be made until you are satisfied every detail is fully covered and exact.  You now have the pattern for your staircase.