Finished up the pergola today, attaching the top vertical boards. Here’s a picture, looking out to the empty lot in back of us (there’s lots of empty lots around us at the moment).

I had been contemplating how to get the spacing correct on those boards. I knew the width of the top rail (119 inches), and the width of the boards (2×6 inches). After some test runs, I figured out the front overhang (12 inches on the top edge; the edges have a 30 degree angle cut).

But how to space them? Then I remembered watching an episode of “This Old House”, where they talked about how to space the balusters (vertical boards) of a porch railing. After some Googling, I found a discussion of the process to figure out the spacing for stair rail balusters:

Determine the max clear area allowed by code (4″ locally), add the width of
baluster. Then divide that number into the length of railing to receive
balusters. Round up that number to the next whole number.Place your tape in
lower start corner (back off half the width of a baluster to start). Pull the
tape to the end plus half the width of a baluster. Remember that whole number-
move the tape diagonally (holding start point) up until you can get a number
that is a multiple of that whole number. Then mark at the multiple number. Use a
level to transfer number up. This should divide the balusters so that the space
between is slightly less than required by code & be equal. Place another
mark half the width of the baluster to one side of the center line mark so you
can see where to place edge of baluster. Check that you did it right. Example:
So if you have a 4″ clear space and 1 1/2″ balusters, you can use the 6″ mark
when the tape is stretched on the diagonal based on a multiple of 6″ x rounded
up whole number from the length divided by 5 1/2″. Start 3/4″ before calculated
start and 3/4″ past end.

Got that ? Me either.

So I found this page http://www.virginiarailingandgates.com/calculations.asp with a baluster spacing calculator. I knew that I had 16 rails, so I added played with the numbers until I got the result of 18 top rails (including the end one, which I wouldn’t install). That gave me spacing between each rail as 6 inches.

So I cut a scrap piece of wood to 6 inches to be my spacing template. I placed all the railings with their proper spacing, then used another piece of scrap cut for the overhang length on the back side. I got all the railings ‘dry placed’, and then looked at it from all angles to make sure that it looked good.

All was well, so up the ladder with the 2 1/2 inch deck screws, the cordless drill, hammer, and my wood spacers. I started on the back side to practice my fastening technique. My plan: one screw on each side of the rail, angled down into the support rail. And I used the hammer to help get the screw started.

The technique worked, so I continued on the back side, using the wood spacers to get the proper spacing and overhang. I did notice that I should slightly offset each screw from the center; if you don’t, the second screw hits the first one and the wood will split a bit.

Once all the back end screws were done, it was off to the front. I just needed the 6 inch spacer board, more screws, and a recharge of the cordless drill battery (note to self: next time, charge the battery overnight, although waiting for a recharge gives you a nice break from your hard labors).

So the pergola phase of the back yard project is done. Next phase is prep work for the brick pavers underneath.

Not only did I finish the pergola, I also gave the back yard it’s first mow since the sod was installed. A nice professional diagonal mow, with once around the edge.

And that was enough for one day. I spent the rest of the afternoon sitting on the shaded back porch, doing a bit of reading, and watching the jets from Hill Air Force Base fly by on their way to the training range on the other side (west) of the Great Salt Lake. Temps in the high 80’s, but a little breeze made it pleasant.