Wednesday, October 5, 2011

How We Did It

Several people have asked how we knew the size of the porch, and how we calculated the stairs. It's half history and half science.

For the porch, it was pretty easy: we have the original porch posts, along with the porch railings an top pieces. So determining the size of the porch was simple: we laid out everything in the dining room, and then measured to see how long and how wide the porch should be. Andus had made detailed measurements of the house for the plans, so the original porch size was replicated on the house for its new location on 62nd Street - so the plans were another source of information. When it's done, the porch should look like it always did, with one exception: on College Avenue, the opening for the stairs was to the right, as the stairs went down in front of the bay window. On 62nd, the porch stairs will go right up to the front of the porch.

Determining the stairs takes more work. Eric and his crew put in a concrete first step as part of the foundation for the porch. Once we built the porch, we measured the distance from the porch floor to the foundation (height) and then the distance from the edge of the porch to the leading edge of the concrete step.

Then the fun begins: I had to determine how long each step could be (the "run") and how high each step could be (the "rise"). Usually, when you measure, you end up with numbers that are very difficult to divide: 62 3/8" long and 47 9/16 high. But this time, I lucked out: the height (from the concrete step to the top of the finish floor on the porch) is exactly 42 inches, and the run is exactly 54 inches. So the rise of each step (assuming 6 risers) would be 7 inches, and the run would be 9 inches. (six treads).

Each step needs a nosing, the overhang that sticks out over the next step down, which is generally 1 to 1 1/2" So I determined that the tread (the run plus the length of the overhang) for each step would be 10 1/2.

To check the math, there are three formulas to examine, to ensure the stairs are the proper dimension. Taking the rise (R) and the tread (T), the stairs must satisfy at least one of the following:

T + R = 17" to 18"
2T + R = 24" to 25"
T x R = 70" to 75"

Our stairs meet all three requirements: T+R is 17 1/2", 2T + R is 24.5", and T x R equals 72.5". It doesn't get much better than that.

So now that I was comfortable that I had the right dimensions, it was time to cut the stringers. Tom first helped by "crowning" each of the 2x12s - each board has a curve, and so we wanted to make sure that slight curve was pointed up (to make the steps as strong as possible).

Each step makes a right angle on the stringer - the angle between each riser and the step below it. So I took the framing square, and set one side at 7" (the rise) and one side at 9" (the run). I set the 7 and the 9 at the edge of the 2x12, and then I traced the right angle between the two, which made the first full step. Next, I slid the framing square down to make a new right angle just below the first one (the 7" riser being lined up right where the 9" run ends). This is repeated four times, one for each full right angle on the stairs (the top step is just the tread, as the riser is the side of the porch, and the bottom step is just the riser, the tread being the concrete).

Each treat is 1" thick, so I subtracted one inch from the bottom step, so all the finished steps would end up being exactly the same height. I also put the top step 6 1/4" down from the porch, since the tongue and groove porch flooring is 3/4" thick (so the total distance to the top of the flooring is the same as each step - 7 inches).

Once the stringers were drawn on the 2x12s, we measured to make sure the distance from the right angle (where the riser meets the tread) and the back of the stringer was more than 5" (another code requirement, to ensure the stairs are strong enough). Our stringers met this easily, so we were ready to start cutting them out.

Then using the circular saw (which is a tool I definitely can no longer use, particularly for making stringers), Tom cut along the lines I had drawn. A circular saw cannot reach the corners of each step (not without cutting into the stringer) so after he cut them most of the way, I used a draw saw to make the remainder of the cuts.

The last step was making the cut out at the bottom of the stringer for the sole plate - this prevents the stringer from sliding forward.

We put the first stringer in place, and tested to make sure it fits. It was a perfect match, so we took it off and used it as a template to trace all the other stringers. We made three more of them, and installed them on the porch.

This weekend, we'll make the remaining three stringers, and install them as a full width set of stairs. And then we'll start rebuilding the porch roof.

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