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Installing Stair Railings

- Continued Whoever invented the rail bolt did stair builders a big favor. It's used for blind fastening of rails to posts, and also to join two rail sections together as needed (Figure 9). On one end it's a threaded screw, and on the other end it's a bolt. The screw end goes into a predrilled hole on the post or on one railing section; the bolt end goes into a hole in the other rail. But first we predrill a 1-inch hole under the railing, just big enough to get a nut through. We insert the nut from underneath and tighten it onto the bolt to bring the assembly together.

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Figure 9. Where two rails meet at a post, only one side can be screwed. The other side is attached with a rail bolt. One end of the bolt has screw threads for attaching to the post; the other end is machine-threaded to accept a nut. A pilot hole for the bolt in the end of the rail and a 1 inch hole for the nut under the rail are prebored at the shop. In the field, the installer has to drill a pilot hole in the post, attach the bolt, and then tighten the nut on from beneath the railing. A plug hides the hole in the rail.

With an over-the-post rail system, we preset all the rail bolts. Where there's a joint, we attach the rail bolt to one railing and predrill the 1-inch hole in the matching piece's butt end. We preassemble the whole railing in the shop to make sure it's right, then dismantle it and ship it. All the installer has to do on site is put it back together and tighten it up. Balusters. The treads and the rail have been predrilled in the shop to receive the balusters. The bases of the balusters are level with the rails, but the upper turnings are rail-oriented — the profile follows the pitch of the railings. In the field, I install the center baluster first, then sight the railing to make sure it's straight (Figure 10). In fact, I like to put a slight crown to it, on the assumption that it might sag over time.

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Figure 10. The author slides a baluster into the predrilled hole in the railing, then lowers the pin into the hole in the tread. He sights the rail: It should have a very slight crown.

I also double-check the railing height. The rake rail height should be measured plumb from the top of the tread at its tip to the top of the rail (Figure 11). Our local code calls for a 34-inch rail height, but that varies from place to place. I marked my level at the 34-inch height so I can make a quick measurement perfectly plumb without having to use my tape.

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Figure 11. Railing height should be measured from the front and top of the step, straight up to the top of the railing. The author uses his level, which is marked for 34 inches, the code-prescribed rail height in his locality.

If the railing is at the correct height, I proceed to install all the rake balusters. I first measure and cut each baluster to length. Then I take the baluster, line it up with the hole in the rake rail, push it up, slip the pin over the hole in the tread (which we have first squeezed a little glue into), then drop the baluster back down (Figure 12). At the top, I predrill a hole and put in a 4d finish nail. At the bottom, we send in one 6d nail to keep the baluster from spinning. The nail goes about 3/8 inch from the top of the tread, on a 30-degree angle going into the baluster, so it goes right through the pin and connects into the tread.

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Figure 12. The author fastens the top of the baluster with a 4d finish nail and the bottom with a 6d finish nail.

Level balusters.

Unlike the rake rail and the stair treads, the level rails and the upper landing treads are not drilled in the shop. Again, the contractor on site may have his own preference for laying out and attaching these elements, or a discrepancy on site could affect the spacing between the post and the wall. So before I can install those balusters, I have to mark and drill the landing tread and railings (Figure 13).

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Figure 13. The author marks his hole centers with dividers (above left), drills the holes, and transfers the hole centers to a story pole (above right), then transfers the same layout onto the underside of the rail (left).

I use dividers to mark the landing tread, but first I have to figure the spacing. I look first at the spacing of the balusters on the stair treads; I want the landing balusters to be in that vicinity. Say it's 4 1/2 inches: I measure the distance between the landing posts (which happens to be just under 4 feet) and divide that number by 4 1/2 inches to see how many spaces I need to mark off. The answer is 10 spaces so I divide the total distance by 10 to get the interval, which is close to 4 1/2 inches. I set that distance on my dividers and step it off to mark the centers of the holes. I drill the bottom holes first, then transfer the centers to a story pole that's cut to the length of the rail. I use the story pole to transfer the marks to the underside of the rail, and then drill the upper holes.

Finishing Touches

Once the balusters are in, all that's left is a few trim pieces. At the mid-landing, I install a couple of pieces of baseboard. I place the baseboard on two scraps of the actual flooring material to elevate it, so that the flooring contractor can slide his material under there later. Base cap molding goes on above the baseboard. I also apply base cap below the fascia around the upper landing, using 8d gun nails. Here, the base cap is flipped upside down (Figure 14).

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Figure 14. Using 8d nails, the author applies base cap molding around the stringers and landing baseboards. He uses the same material flipped upside down below the stringers on the open side of the stairs, and below the fascia around the open landing.

Cove molding covers the joint where the fascia butts up under the landing tread. Cove molding under the stair treads was already applied at the shop in the same way; but on site I still need to place a couple of final pieces of cove under the landing treads at the top of each run of stairs. To finish up, I plug all the 3/8-inch countersunk screw holes with wood plugs and sand them flush. Stair builder Paul Alves is production coordinator at Cooper Stairworks in Somerset, Mass.