As you may recall, late last year I stopped work on the bridge
due to an injured rib. At the time
the footbridge looked like this:
I started work on the railings after the snow thawed and I'd completed the normal spring forest maintenance. I finished the railings on May 23rd. These next four pictures show the bridge as it looked then. Note that at the time of these pictures I still had work to do on the paths leading up to the bridge, and had yet to complete the facial panels on the undersides of the north ramp. Also, the waterfall/stream/pond had not been restarted. All that would be completed by the 31st, which I'll cover in a future post.
The rest of this post describes the construction methods used on the railings.
Railing design is subject to local building codes. I am absolutely
NOT an expert, so please do not rely on anything written here. I strongly advise you to do your own research for your situation. Having said that, typical building requirements include: 1) minimum railing height (36" in my case), 2) maximum width of any gap in the railing (4" for me locally, but this apparently varies), 3) railing design does not allow youngsters to "climb" the railing using horizontal footholds and the like, and 4) strength guidelines, which are pretty complex. In addition for stairs there is a requirement for a grippable hand railing, which I did not provide. There may be other requirements I missed -- please don't trust this write up for your situation!
There is also a wide variety of choices in railing material. This includes pre-constructed railing parts made of special materials, which I rejected due to expense, and pre-constructed railing sections of cedar, which I rejected due to appearance and poor strength. I eventually decided to stick to redwood -- the same material as the surface of bridge. Posts would be 4x4s (nominal 3.5" x 3.5"), balusters (those thin vertical pieces of wood between the post) would be 2x2s (nominal 1 3/8" x 1 3/8"), and the top railing would be 2x4s (nominal 3.5" x 1.5"). The total cost for the railing materials was close to $1k.
For construction all pieces were given a first coat of the same stain as the rest of the bridge BEFORE they were assembled. This serves two purposes. First, after assembly there are always places where the wood is joined that is exposed but can't be reached with staining tools. Pre-staining provides at least some protection for those areas. Second, it's easier to stain the parts of a railing in bunches on their own, as opposed to after they are all assembled.
This custom footbridge has a lot of unique areas in terms of how it was constructed, so I started the railing at the simplest section -- the part of the bridge over the creek. This is very nearly level and each side of the bridge is comprised of a 2x8 length of redwood attached to two 2x8 pieces of pressure treated (p.t.) fir -- making attachment of the posts relatively easy. I started by cutting 4' lengths of 4x4 post in half, giving me 4' high posts. The posts were to be connected to the bridge sides with 2 screw-end lag bolts = 1/2" x 8" long, with a matching washer. The top of the posts were to be 35 3/4" from the bridge floor -- which meant that with the railing top the railing height would be about 37 1/4". (This just seemed a good height.)
Note that this means part of the post extends below the bridge bottom. I considered trimming off the excess, but after looking at a number of pictures of railings in books decided I like this look. After doing the same thing with the balusters, this created a visual sense of the bridge gently transitioning from the bottom of the floor of the bridge to the scenic area underneath, rather than a sudden cutoff.
The assembly method I settled on, after some trial and error, was as follows. I first measured the appropriate locations of the lag bolts on the post. The idea is that you want to keep the lag bolts as far from each other as possible, but also make sure both will be firmly anchored in the wood. I then drilled two holes using a 7/16" bit -- just slightly smaller than the 1/2" lag screw so that it could have some wood to "grab" to. Although I did everything possible to make the drill holes straight, some slight variation is possible, so I measured the location of the exit holes relative to the entry holes, vertically and horizontally. Typically the offset was no greater than 1/16", but on some occasions it could be as much as 3/16". Taking the offset into account, I marked the corresponding location of the top drill hole onto the side of the bridge. I then used a 3/8" drill bit to make a hole in the bridge side (keeping it as level and as perpendicular to the bridge side as possible). This meant that it would be a lot of work to get the 1/2" lag screw into place, but once into place it would hold tightly. (My drill was not strong enough to drive the lag screw -- I had to use a large manual rachet.)
Holding the post closely in place, I screwed in the lag screw (with washer) through the post then partly through the hole in the bridge -- enough so that the post would stay in place unless I intentionally moved it. Then I verified that the post height was correct (if not, adjust). Then I used a vertical level to set the post straight and used a drill with a long bit, put through the second post hole, to mark the location of that hole on the side of the bridge. Be careful to center the marking as much as possible. Once marked, drill the second hole with a 3/8" bit, then add the second lag screw. As I got close to finishing the tightening of the lag screws I used the vertical level to see if the post was leaning inward or outward from the bridge, and if it was used shims (of p.t. fir or redwood) between the post and the bridge to make it as upright as possible.
Ok, posts are now in place. The railing was comparatively very simple (assuming top of posts are level and in a straight line). Measure the length, cut, sand, stain, then attached to the tops of the posts using 3" deck screws -- 4 per post. Where the railing piece would share the top of the post with an adjacent railing, use 2 screws.
Balusters were also 8' lengths which I cut in half -- so each baluster was a 4' length of 2X2. You want baluster spacing to be even and to have each one as vertical as possible. At the same time, because wood pieces tend to warp or bow you need to account for possible warpage and visually adjust the location of each to make sure it all "looks" decent and keeps within the code requirements for maximum spacing.
My process for attaching balusters evolved, like everything else, through trial and error. The first step was to decide the exact placement of each one. While the code discusses the spacing between each baluster, many of the builders on web sites talk in terms of center-to-center spacing. I decided on a center-to-center standard of 4" -- which is closer than necessary. In part I did this because I wanted some extra room just in case two warped balusters were placed next to each other, creating an extra wide space. But even allowing for an extra "safety space" I think I could have gotten by with 4 7/8" or even 5" center-to-center spacing. But, 4" is the standard I started with, so I stuck with it.
The next question is the spacing between the post and the first baluster on each side. Because posts are not evenly spaced on this bridge this is something that has to be figured out anew for each section. I eventually came up with this process. First measure the distance between the posts. For example, let's say 50". Then divide by 4" to get the remainder -- in this case 4x12 = 48 so the remainder is 2". Add 4" to the remainder (in this case summing to 6") and divide that number by two (result in this case: 3"). This number is will be the distance between the *edge* of the post and the *center* of the first baluster. If you do this on both sides, then all other balusters will automatically be spaced 4" apart. (Note that in some special cases this might not yield a desired result, and if so you can adjust the center-to-center spacing slightly. It's all subjective.)
To attach the baluster to the rail I used 10d 3" nails -- the kind with a stub head so they can be easily hidden with putty and stained over. You can nail these in directly, but with redwood doing so every 4" in a line is prone to creating a split in the wood. So I drilled each hole with a 1/8" bit then hammered the nail in until about 1" appeared below the rail.
At that point I positioned each baluster onto the nail from underneath the railing -- taking care that the center of the baluster matched the center of the rail and the edge of the baluster matched the inside edge of the rail. I then hammered the bottom of the baluster (not the nail, but the bottom of the wood) until the baluster was on the nail and flush with the bottom of the rail.
The bottom of the baluster now will swing a bit in each direction. Using a measuring tape I found the correct position for the bottom of the baluster, relative to the next baluster or the post, and drilled a pilot hole through the baluster and the side of the bridge with a 1/8" bit. Then used a 3" deck screw to fix it in place. Because wood is not always straight the distance between the posts at the rail level may be slightly differnet than the distance between the posts at the foot level. In addition, some posts or balusters may be slightly warped. Therefore, it is best to stand back a few feet and check appearance every few balusters to make sure that everything *looks* like it is lining up right. Once the baluster is screwed in place at the bottom, hammer in the rest of the nail at the top.
Although this sounds like a complicated process once you get the hang of it you can do it very quickly if the balusters are already cut and stained. I typically did 6 balusters at a time -- starting at the posts and moving inwards, 3 at a time from each side. I didn't do more at a time because I felt that hammering in nails on the rail board at a distance of more than 3 holes from the previous fixed baluster risked splitting the rail wood.
After I completed the railing on the main footbridge over the creek I found that the rest of the railings all had a few extra complications. One issue was post anchoring. At the bottom of the stairs there was not a natural anchor place for the post. There were redwood stringers on the outside but no wood on the other side of the stringer for the lag screw to attach to. I had to pull up the stair planks temporarily and add some leftover bits of p.t. fir, cut to size, to fit between the redwood stringers and the inner p.t. stringers. I also found i had to cut the bottoms of the posts at the bottoms of the stairs and at the top of the south ramp where they came close to the ground. This would also be true for the balusters in those locations.
At the top of the stairs I had to adjust the metal straps that were used to hold parts of the bridge together, in order to create spaces for the lag screws. This required unassembly and reassembly of the straps, at one point a fairly involved mini-project. At the post across from the stairs the edge of the bridge floor was curved, and the edge of the bridge is 2-to-4" from the underlying beam. In order to create an anchor surface for the post that was aligned, vertically, with the edge of the bridge floor I again had to miter some p.t. fir and use 6 4" deck screws to put it in place against the beam. The 8" lag screws were long enough to penetrate this extension and still firmly grip the main beam, and as such that post is as solid as any on the bridge.
Finally, on the north ramp the sides of the bridge floor fan out as far as a foot from the underlying joist. Since that was just a single 2x8 p.t. fir joist -- not a 4-6" thick beam like on most of the bridge -- and because it was so far from the edge, there was no good option for anchoring the posts to the bridge itself. So, instead I installed two concrete post footings, each fixed in place with half of a bag of concrete installed around the footing. This sounds like a lot of work but actually was one of the quickest tasks of this project -- taking only 40 minutes for the two posts. The posts were then put in place against the bridge facias and used 5" lag screws to the facias -- not for vertical support but only horizontal support. I was prepared to add a horizontal beam underneath the bridge between the two posts for additional horizontal support, but when installed that turned out not to be needed.
Another challenge was uneven post tops. Where the bridge floor was sloped the railings had to be sloped to match, so the post tops did too. I tried a number of measuring techinques, but in the end the best was to position the post in place and draw a faint line where the floor went against the post. Then add 35 7/8" along the line and cut the top of the post there. In some cases the post had different slope where it would support two railings that came in at different slops. In that case the measurement had to be done twice, once for each slope.
Railing edges were also more interesting if slopes were involved. In one case I made 12 separate miter cuts to get it exactly right. All I can suggest here is to be patient and expect to make many cuts if there are many angles involved. And be prepared with stainable wood putty if something goes wrong. Also count on sanding the rails afterwards so that transitions from one railing piece to the next will be smoother.
Baluster tops, like post tops, had to be cut at slopes. The advantage here is that the cutting could be done after the railing was in place. So, using the vertical level, set up a baluster (the straightest one you can find) in place and mark the angle against the railing. Set up the miter saw at that angle and note it (like, 3.5 percent, for example). Cut one baluster and test. Adjust if needed and cut another. Repeat until it's perfect. Given the natural variation the first one is probably usable even if not perfect, but it's worth adjusting until you have the angle right. Then cut all the rest at that angle.
For baluster spacing you have to make an accomodation for the slope. If you want 4" spacing horizontally that will be slightly longer spacing if you measure at the top of a sloped railing. In this case determine the spacing of the balusters nearest the post as described before. Then measure the spacing along the top of the railing between the two holes that are nearest the post. For example, let's say that horizontally the distance between the two is a multiple of 4" -- say 40". But along the top of the sloped rail it's actually 40 5/8". In that case add 1/16" (1/10 * 5/8") to the distance along the top of the rail between each hole. And make sure to drill the holes vertically -- not along the same slope as the rail.
One more point is that code has special rules for stair railings, and one issue is height. Because the railing is linear and the steps are not, you can't develop a single measurement for the height of the railing relative to the step, but instead the code uses a height range. I tried to make sure my railing was at the middle of the range.
Finally, there is the issue of the curved railing. At one part of the bridge -- the side opposite the staircase, the edge of the floor is curved in a quarter circle. I felt that if I used a straight 2x4 railing connection between the posts on this side it would look bad. The balusters would have to be angled in order to connect from the bridge side to the railing, for one, and the connection would just be wrong.
After considering a number of options I decided to use 2x6 planks for these railings instead of the normal 2x4, and to use the extra width to cut the planks to match the floor edge curvature. The outside edge of the railings was installed along the post edges as normal -- that is the outside edges of the railings lined up with the outside edges of the posts -- thus leaving the inside edges sticking over the bridge floor. Then using a very careful and multi-iteration process, I measured and cut away the extra parts of the railings until they matched the floor edge curve. The railings were given extra sanding and now look natural with the balusters in place.
Next post: red clay pathway and getting the water feature running.
