How to build a simple bridge
Decades ago, when my wife, Melody, and I had corporate careers, we dreamed of a peaceful retirement home with streams, ponds, and wildlife. Before 1900, when North America was largely rural, people liked to visit their local town to shop and attend Sunday church. Things started to change after rural people moved to crowded urban areas where they had frequent and daily contact with others. Like other city-dwellers today, we longed for the distance and pleasure of coming to a crowded city on our own terms.
We were hoping to build our half-timbered dream home on a quiet rural property, and in 1995 we found land about 10 miles southwest of town, thanks to my persistent wife and some good real estate agents. Our land included a weekend house next to the pond and a bridge. Both structures needed to be replaced or, at the very least, undergo major repairs. Over the next two years we camped on the weekends and felled about 75 trees, and demolished most of the pond house because it was suffering from a termite infestation. I purchased (and still use) a used Ford 555B tractor with a backhoe and front bucket to do most of this work, including installing nine underground culverts. We have built our dream house. It has been one of the most interesting, stimulating and enriching experiences of my life! And today we enjoy the fruits of our labor and the sweet sounds of nature.
Living on our beautiful property, we had to deal with three wooden bridge designs in one location – including two replacements that we built with the help of good neighbors. Here are some tips on how we planned and managed these projects.
Wooden Bridge Designs
A small stream runs alongside our long driveway, with a side road leading to a small meadow across the stream. When we bought our property, that first bridge was decrepit and mostly rotten. Fortunately, we didn’t need immediate access to the meadow, so I removed the few remaining planks from the deck with my Ford 555B and considered my options.
My first step was deciding whether to outsource the work or do it myself. I opted for DIY work. I urge you to check your local building codes and laws before deciding. I then learned about the creek, particularly upstream where I spoke to neighbors about their past experiences, such as annual gushing and rare flooding, and how the history of the creek might affect my bridge design. I walked the creek during the dry season and noted the adjacent trees and shrubs, and the animals – turtles, beavers, frogs, fish and others – inhabiting the creek and the banks.
Finally, I probed and carefully examined the ground where the replacement bridge would sit on both sides of the creek bank to make sure it provided solid support for the bridge beams. On our property we had a mixture of rocks and gravel of varying sizes. I packed smaller stones around the larger ones and firmly tamped the area, then added cement to create a smooth shelf. I located the shelf 1 foot below ground level to allow for 10 inch beams topped with 2 inch thick decking boards. It held up well for a quarter of a century!
If your stream banks are loose soil or sand, you will need to dig and pour a concrete footing well back from the flowing water. This footer should be below the frost line and have adequate width and depth; you may need certified technical advice to determine the appropriate dimensions, given the type and amount of traffic likely to use the bridge. If your stream banks are sedimentary rock, you may be able to excavate a resting place for the bridge beams. If the ground is clay mixed with rocks, you may be able to drive in a number of steel stakes to reinforce a concrete slab where the beams would rest. Additionally, you can pack large flat boulders from the creek bed down to bridge level, placed at a 45 degree angle, to channel flowing water to the center of the creek bed.
After working out the details of our replacement bridge, I visited the owner of the Woodpecker sawmill in southwestern North Carolina. We discussed how strong the bridge needed to be built to support the 13,000 pound Ford tractor, plus an extra ton for a gravel-laden front bucket.
The factory sawed and delivered five beams, each 10 feet long and 10 inches square, plus 20 2×6 boards 12 feet long, all white oak. I put them in place with my Ford and a crowbar, and bolted the decking boards to the beams. This second bridge lasted about 20 years, after which some of the 2x6s had to be replaced by our good neighbor and sawmill owner Joe McGee. During this process, I discovered that the five beams were rotting!
Bridge No. 2 collapsed in the spring of 2021, when I was driving the Ford tractor over it. Luckily I was able to safely get out of the creek bed by starting the engine. So, I ripped out what was left of that bridge and set about figuring out where to replace it.
Bridge No. 3
Another neighbor, Jon Neamand, had just set up his own sawmill. He agreed, for a fee, to saw white oak beams from local trees so that I could build the third bridge. For the beams, he used heartwood oak from dead trees, already dried and ready to be coated with a proven oil-based preservative of Jon’s invention. The decking oak needed to cure for a few months and then it would be treated with a single coat weatherproof sealer.
To assemble the bridge, a chain was attached to the center of each oak beam, with the other end of the chain connected to the bucket of my backhoe, then I carefully lifted and maneuvered the beams into place, one at a time , with Jon nudging each one into their precise location. He placed five beams this way. Next, Jon screwed the decking boards to the beams below. We used stainless steel wood screws between 3 and 6 inches in length as needed for this project.
We placed a buttress board at the ends of the girders and a decking board covering this buttress, to drain the water into a 12-foot-long gravel-filled trough at both ends of the bridge. Next, Jon squared off the sides, cutting off the uneven ends of the decking.
Since then, I’ve driven frequently and confidently across this sturdy bridge with everything from an SUV to my loaded tractor to a garden cart. I hope this third bridge will last 30 years. Or maybe it will stick around to eventually be discovered and admired in a future archaeological dig.
Bob Heltman has been a US Air Force pilot, business executive, fisherman, hunter, and more. Over the past 25 years, he has installed nine culverts, built a dam and moved countless boulders on his property outside of Hendersonville, North Carolina.