The plan drawing showed the path extending south from the bridge, curving in an "S" to carry to the steps at the front of the porch. The intent was for the path slope to be gentle, avoiding the need for steps.
On paper this looked like a good design, and before I began the bridge I verified that the slope would work based on the height to be gained and the distance of the path. However, as the bridge took shape I could start to visualize the plan in the actual setting in 3D, and concerns set in.
The problem was that in order to acheive the gentle slope most of the path would need to be elevated -- some parts over 3' above ground. Now, a short bit of elevated path is a nice feature -- but normally you want the plant and trains no lower than foot level, and in many cases ideally raised above the pathway. A long stretch of elevated pathway would be opposite that ideal -- making the garden seem distant from the viewer. In addition, it would visually bisect the garden and make it more difficult to construct intersecting paths. In short, the plan just wasn't going to work.
One alternative was to keep the path location as planned but have it follow ground contours. But this required introducing steps, something I wanted to avoid. Not so much for handicapped access but rather for ease of snow removal. (3 foot snowstorms aren't common here, but they aren't rare either.)
I started thinking about this problem before the north ramp was even started, so eventually I came to a solution. The south ramp would be shorted by curving it to the right, where there is a rock wall. The ramp would end at the top of the "cliff" and the path would continue to the north side of the porch. This preserved the concept of a gently sloping path to the porch. However, in order to provide access to the main garden south of the stream, a stairway would be added down from the ramp.
This is hard to visualize with just words, so here is a picture of the full bridge including ramp on Sept. 27 after the main structure was complete, but before railings and side trim were added:
In this picture you can see how the ramp curves towards the rock wall to the left, where it transitions to a ground pathway. You can also see the staircase that allows people to access the ground level paths on the south side of the stream.
Before I settled on the plan above I consulted with my wife, and she agreed. Then construction planning began. I was quickly clear that this section was going to be quite a bit more involved than the first two.
Construction started on September 10. The first step was to plot out the ramp. I used my trusty can of cheap spray paint, two tape measures and the 6' level (to verify that the slope wouldn't be too steep). The bridge itself is slightly wider than 3', and I decided I wanted the path to be closer to 4' wide, as it is on the north side. So I marked the exact location where I expected the ramp to end on top of the rock wall, then marked an approximate path the ramp should follow from bridge to the wall. Then I identified the location alongside the ramp that would serve as the top of the staircase. Together these markings defined the rough boundaries of the south ramp.
Then I marked the locations of the post footings. It seemed logical to have two footings at either side of the top of the staircase, and two under the ramp just next to the rock wall. Once those four were marked only one more footing was needed (assuming a maximum span between posts of 5') and that was along the side the path opposite the stairs.
Once marked, the next question was what to use for footings. On the main bridge I used 3.5' deep concrete pilings, required due to the 9' bridge span. I preferred to avoid having to dig and install 5 more such pilings due to the time required. On the north ramp I'd used precast concrete piers, each placed on a bed of mixed concrete, and that had worked very well. I preferred to use that method for the south ramp, but I was concerned that this would not be sufficiently stable given the height of the south ramp -- just over 3' from the ground at the highest point.
Fortunately, the company who makes the precast piers has a web site where they say that heights above 30" are feasible if you install diagonal braces between the posts. I wasn't sure if such braces would be required given the construction I planned -- which would provide extensive diagonal bracing as a side effect -- but this did confirm I could proceed with using precast piers now, and add bracing later as needed.
As with the north ramp I used about a half bag (30 lbs.) of mixed concrete under each pre-cast footing. I also leveled each pier in both directions and made sure the slots lined up between pairs of piers.
For the wooden posts and the beams I bought a bunch of brown 4x6x8 landscape timber. These are super strong and highly resistant to rot. They were also on sale at Lowe's for $11/per -- a savings of $6/per. Unlike finished lumber their dimensions varied quite a bit. For example, the second dimension varied from 5 7/8" to 7" in the boards I got, but fortunately was mostly 6" exactly.
Each precast pier has a 1 5/8" deep slot for a 3.5x3.5" post as well as two 1 5/8" wide crossing slots for 2x lumber on its side. Here is picture that shows how I set the 4x6 posts onto each pier:
The post sits flush on the top of the precast pier. In the slots are sections of pressure-treated (p.t.) lumber cut to fit exactly. You can't see it, but the p.t. sections are attached to the bottom of the posts using galvanized nails prior to putting the post in place. This method results in some wobbling, but it distributes the weight evenly across the pier. The wobbling goes away after the beams are connected.
For my first post I tried an alternative method. I cut the end of the post to fit into the 3.5" x 3.5" post slot in the pier. It worked, but I added p.t. slot sections to that post for additional stability, then decided to simply use the p.t. slot method described above for the remaining posts.
The first two posts I built were for the top of the stairway and thus were easy to size. I set their height to be 1/2" higher than the south end of the bridge (taking into account the expected ramp slope), and made sure they were level with each other. But the next three posts were a challenge because their tops had to be sloped to match the expected slope of the ramp. This picture shows one of the sloped posts after the beams were attached:
In the above picture there is a gap between the beams at the top. This was due to the way the beams were cut, but it gives a false illusion that the two beams were on different slopes -- in fact their slopes are close to identical.
The first challenge was determining the precise slope at the top of the beam. I used a stake to mark the top of where I expected the ramp to be at the top of the wall. I then positioned a straight 12' board, on it's side, between that stake and the top of the stairway post to define the slope. Measured, marked, re-measured a few times, cut, and voila -- it actually worked. That slope was used for the last two posts as well.
Alas, I got the height wrong. For the first post I forgot that there had to be a beam between the post and the planks. Sigh. Fortunately the error was that it was too long. Since the slope was already defined I was able to easily slice the extra 6" off using the table saw and fence. Did a similar thing with the next post when I measured from the top of the level instead of the bottom, but again the table saw solved it quickly.
I mention this because when I'm working on a substructure -- or any project where any single missed measurement will negatively affect the whole thing -- I measure and check frequently to catch errors, and recommend the same to my kids.
With the posts in place there was one more thing to do before installing the beams. There needed to be some sort of beam support on the top of the wall. This picture shows the eventual solution:
I learned from the south side ramp that the transition from the redwood bridge to the clay pathway is a bit tricky. You really want the beams that support the planks to extend as close as possible -- within a couple inches -- to the transition point to provide sufficient support. However, while the clay pathway sits right atop the ground, the support for the planks (beam + pier) is over 12" under the planks, so this requires an immediate transition from ground level pathway to a foot deep under the planks.
For the north ramp this was made more tricky because the end of the ramp was to be very near the rock wall -- a 4 foot high rock wall that kept in place the dirt near the house foundation. I was hesistant to dig too deeply into the ground for fear it would weaken the wall.
In the end I decided to support the beams, which are landscape timber and thus okay for ground contact, with a 6x6 post of landscape timber set into the ground. I fortunatly had a 6x6x8 post already (I'd bought a green 6x6x8 for the main bridge posts before I discovered that Lowe's had brown landscape timbers, which look much better). I cut the 6x6x8 timber into two equal 4' lengths (using a chain saw -- a precise cut was not needed) and used one here at the top of the ramp and the other at the bottom of the bridge stairs.
This part of the project was not difficult logistically, but did require a fair bit of labor. It was easy to identify with stakes the exact location where I expected the beams to end. I marked the spot, measured a space for the 6x6 timber, plus a little space around it, and dug using the pick and shovel. I also had to remove dirt to make room for the beams and to remove the top level of rocks on the wall. Once it was dug out it was a matter of trial and error with progressively smaller adjustments until the timber was in place at the right height, with the correct slope towards the ramp and level from one side to the other. I then filled in the dirt around it and tamped everything down with the tamping tool.
The photo above shows the green timber after it was buried in place and beams added. You can see that I also added some slightly trimmed down 4x6 timber pieces on top of the timber between the beams -- anchored with 16d nails -- to hold the dirt in place.
The end result is that the wall is now more stable than before, The actual rock wall is shorter -- maybe 3' tall. The landscape timber and the other timbers serve to make the dirt behind the wall more stable. In addition, the beams will come to within 2" of the clay pathway edging, meaning the last plank on the beam will be fully supported.
That takes me up to the point where I was ready to add the beams, which will be the first topic of the next post.
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