I have a creek that runs through my yard. Most of the year it’s dry (we live in California), but it has a short span of time in the winter when water flows after the rains. Even when it’s dry, it is inconvenient to cross, because it’s between 3 – 4 feet deep, and the bank is irregular.
Actually I used to have a makeshift bridge over this creek. Years ago, I threw down some scrap lumber I had around. But one day when I came out into the yard, I saw the whole bridge was gone! It wasn’t secured down, so in theory it could have floated away when the water level swelled. Or else I guess someone passing by needed some lumber? Anyway, I need a new bridge.
So I made a plan to build a new footbridge over it. This time I needed to build one properly with concrete moorings. I’m an amateur with construction projects, so this would be a learning experience. I hoped it would inspire me to try other projects.
Preparing the site
The first step was to clear the weeds and brambles that have grown in the creek. It had gotten quite overgrown. The thickest growth was next to my neighbor’s driveway. Some of the weeds could be pulled out by hand, but the raspberry brambles are thorny, and that wannabe tree has grown large enough that I had to use lopping shears and finally an electric saw.
It took several weeks and truckloads hauled to the green waste at our county landfill.
I chose a location to build the bridge. This spot is in the shade of a couple of trees, and the bank was nearly the same height on both sides.
I left the Vinca Major ground cover intact, because it’s nice when it blooms, and also because it’s tougher than it looks, so tearing it out would take a lot of work.
Measuring the bridge
I ran some string to mark out the bridge. I thought I could use 12-foot joists, but I found that was too short. The bank of the creek is pretty crumbly, and I wanted the moorings to be well back from the edge. So I measured out a 16-foot length.
The width of the bridge would be about 5 feet, because I had some Trex composite boards I had kept when we rebuilt our deck. I planned to make these the planks of the bridge, so I could avoid buying new material.
Part of the creek bank is shored up with scrap concrete installed by a previous owner of the property. This was another reason to set the end of the bridge a few feet back from the edge, because I can’t dig through the concrete.
I learned how to make square corners with the 3-4-5 method, and how to tie string to stakes using a Larkshead knot. I enjoyed watching a video Using String Like a Pro, by the Essential Craftsman.
I placed one of the Trex boards on the ground for reference, to make sure I was measuring the right width for the bridge.
How much water?
The creek is dry most of the time, but during rain it does get water. In January 2023 we had one of the biggest rainstorms we’ve ever had in this county. I got a photo of the water when the creek was full, and I was confident that the underside of the bridge (indicated by the string level) would still be above the level of water, and the moorings at each end of the bridge will be secure.
Building the moorings
I planned to have three joists spanning the creek. Trex is not known for its bearing capacity, so I wanted a center joist as well as one on either side. To fix these joists to the ground securely, I would connect them to concrete moorings.
I got steel Strong-Ties to fix the joists to the moorings. I wanted these to be as straight as I can make them, so I built a temporary frame matching the width of the bridge (i.e. 5 feet, the length of a Trex board). These allowed me to keep the Strong-Ties straight as I put them into the concrete. I used construction screws so I could remove these frame pieces from the Strong-Ties once the concrete sets.
The next task was to dig holes to put the concrete moorings into.
Setbacks and getting help
While digging the holes, I gave myself a muscle strain in my back. I’m not used to this kind of work. It’s going to take several weeks to heal and strengthen my back.
So I recruited a couple of friends who were visiting me this summer. I’ve known Jay and Kevin for over 30 years, since we were at university together. They asked if there’s anything I want to do during their visit. I suggested half-joking, “do you want to help me build a bridge?” They laughed but said, “yeah, well, okay!”
Wow, did they help! They made sure I didn’t lift anything so I didn’t re-injure my back. I ended up becoming the foreman, and provided a detailed plan, the tools, and the materials. They said they were there to provide the hands and muscles. But they gave plenty of good input to make every step work well.
Concrete moorings
We dug six holes for cardboard sonotubes, which we carefully leveled at the strings I had stretched. We mixed nine 60lb. bags of concrete and filled the tubes. We also pushed pieces of #3 rebar into the concrete to help prevent cracking.
Then we pushed my Strong-Ties on frames into the concrete. These will remain level and straight while the concrete sets.
After the concrete set for 24 hours, we removed the frames from the Strong-Ties.
Joists
We ordered some lumber from Home Depot: six pressure-treated boards, 2×8 inches by 16 feet. We lifted the boards into position, two in each Strong-Tie.
I had viewed many YouTube videos recommending to “crown” the boards, orienting any bend in the board up so it flattens out when there is weight on it. But these boards were remarkably straight already, so it didn’t matter much which way we oriented them.
We also lined them up carefully and measured from corner to corner to make sure the layout of the boards was still square.
To make sure the tops were flush before we screwed the boards together, we used clamps and held them against a piece of scrap 2×4. Also more clamps to hold the boards tightly together while we put screws in.
The boards were to be bolted to the Strong-Ties. It was a bit of a challenge to drill straight holes accurately enough to emerge through the hole in the other side of the Strong-Tie, but with practice we got pretty good at it.
We got through 10 out of 12 bolts using an impact driver with a socket, but then my cheap old 1/4″ socket adapter broke! No problem! We couldn’t let that stop us. We tightened the last two bolts the old-fashioned way with wrenches.
We now had three strong joists that were level, square, flush on top, and definitely not going anywhere.
Blocks
It’s recommended to add some transverse pieces to provide stability and keep the joists from twisting or leaning. These are called blocks. We used a seventh 2×8 board, cutting it into pieces one by one. We aren’t precise architects, so despite trying to make the framing square, each block was slightly different in length. We screwed them into the joists toenail-style. These pieces won’t be load-bearing.
The bridge was now quite stable. Kevin tested it by walking across it like a balance-beam.
Joist tape
It’s a good idea to protect horizontal wood from any potential rainwater pooling on it, so we got some special adhesive tape used for deck projects and stuck it down on top. The 3 inch tape worked well, and we got it down the first try by going slowly and carefully. One 50 foot roll of the tape was perfect for three joists, with minimal waste.
We didn’t tape the blocks, because they should be under the deck boards, and I assume risk of rot isn’t as important since they aren’t load-bearing. Also because we ran out of tape.
The shiny tape makes the joists look classy. It’s almost a shame it’ll be covered up by the boards.
Deck boards
Now finally we can put the boards on top. We had just enough Trex boards to cover the length if we added a 1/2″ space between each board. That’s recommended anyway for drainage and allowing for expansion (not so much for Trex, but still not a bad idea).
We got very focused on the work during this phase, and didn’t take many photos, but my wife got one of us working.
It really paid off that we made the Strong-Ties level, and made each pair of the joists flush. This made it easy to attach the deck boards to the joists. Our worst fear is that the middle joist might be slightly too high, and the boards wouldn’t sit flat or be stable. But in our case, it was perfect.
After we finished, we were amazed that my impact driver put in 48 coated screws, 12 bolts, and 192 deck screws on a single battery charge. Good job!
Finished product
Here’s how the bridge looks now. Later I will make a bit of a ramp with gravel so it’s not such a high step up, but it works, and it’s strong and solid!
Final thoughts
This turned out to be a surprisingly great experience to build this bridge with my best friends. They are easy-going, patient, practical, communicate well, and they focus on getting things done. By the end, we were very proud of having such a good result, but the time we got to spend working together will be a great memory.
What’s the next project?
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