How to Build a Log Bridge

Follow these instructions and diagrams for constructing a simple log bridge to give your property a rustic look.

By The Mother Earth News Editors
Published on May 1, 1984
article image
by AdobeStock/Vic

“I tell you what. I’d just about bet my little pickup against a pocketknife that this thing’ll hold up a cement truck.”

That was Rick Compton’s wager about the 14-foot log bridge he and Hoy Gross were finishing out at the MOTHER EARTH NEWS Ecovillage. And if you’re curious to see what took place when we did drive one of those massive vehicles over Rick’s completed structure, see the Image Gallery. Go ahead… we’ll wait.

Pretty impressive, huh? Well, don’t let Compton’s success go to your head. We’re going to tell you everything we can about how to build a log bridge. A simple,”no suspension or trusses just lay down some logs and flooring” bridge… the kind of farmstead structure that’s intended for getting you over drainage ditches or small streams. In doing so, we’ll call upon wisdom gleaned from Rick’s considerable experience, and all the relevant research and calculations we could muster. But let’s get one thing clear right now: We don’t guarantee that any bridge you build will bear up to a load like a concrete truck. So if you start to drive the front wheels of an extremely heavy vehicle over your stream-spanner and you hear something begin to crack… BACK UP QUICK!

Main Tools and Steps

An untrussed bridge is simplicity itself. Step one: Build a good base on each side of your waterway. Step two: Lay some stringer logs across the span. Step three: Add flooring. (Mind you, there are a few extra touches and tricks of the trade we’ll be telling you about.) The main tools you’ll need are equally basic: a tractor or pickup truck with a chain for pulling logs… a chain saw… an ax… a bark peeler and adz (if you don’t have these, you can use your ax instead)… a chalk line… a level… a couple of scrap 1 X 8’s or similar boards… some roofing cement… a shovel… a couple of peaveys… and a heavy hammer (see Fig. 1). You’ll also need a helper with a stout back (bridge building is definitely a two-person job).

Of course, you’ll need some logs, as well. Around these parts, folks generally use the amazingly durable black locust. But plenty of other woodsassuming they’ve got more heartwood then sapwoodcan do the job. Bald cypress (old growth), Arizona cypress, catalpa, cedar, chestnut, juniper, mesquite, several of the oaks (bur, chestnut, gambel, Oregon white, post, and white), redwood, Osage orange, and Pacific yew are all quite decay-resistant (especially the last two). You say you don’t have any of those? Well, bald cypress (young growth), Douglas fir, honey locust, western larch, swamp chestnut oak, eastern white, longleaf and slash pines, and tamarack are all moderately durable. However, if you’re stuck using alder, ash, aspen, beech, birch, buckeye, butternut, cottonwood, elm, hemlock, hickory, magnolia, maple, red or black oak, most pines, poplars, spruces, sweet gum, or true firs, you’d best inspect your bridge logs often!

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