|Written by Bill Hanks|
Do you have an area of your backyard or garden that has a ditch to cross? This article will explain, in a step by step process, how to construct a ditch bridge, that is strong enough for a person or even a lawn tractor to cross. Bridge construction is not as hard as you think. A small garden bridge can even make your backyard or garden more attractive.
Planning and Construction
Step 1. Decide on your dimensions. Measure length and width of your bridge, You want it wide enough, to be able to drive your riding mower over. A width of 60 inches should get the job done.
Step 2. Just like a floor has floor joists that run from one wall to another, so does a bridge. Most of these are 16 inches apart. You can make a stiffer bridge, by placing your joists 12 inches apart.
Step 3. The greater the span (distance across), the deeper a bridge joist needs to be. You can add strength and reduce bouncing by adding 4 by 4 posts at the center of your bridge on both sides. These posts need to rest on a 6 inch concrete pier in the ground. These piers need to go below the grounds frost line. A frost line is determined by where you live. For example, in the Midwest, it is 32 inches.
Step 4. Figure the lumber that you will need. I suggest treated lumber, since the bridge is outdoor and over a low water draining area. Cedar and heart redwood look great for a yard or garden bridge.
Step 5. I would build the bridge just like a traditional wood sub floor. This means that a rim joist or band board is nailed to the ends of the bridge joists. This framing member keeps the joists from falling over like a house of cards, when you walk or ride over it. It also allows you to build the frame for the bridge in the yard and drop it into position with the help of several friends.
Step 6. Depending on the length of your bridge, you have to decide what you want the ends of your bridge joists to rest on. Some individuals prefer concrete pads, railroad ties that are buried to ground level, or just the ground itself. I like the idea of a concrete pad 6 inches wide and at least 8 inches deep. after all you need concrete for your pier posts. This pad needs to be as wide as the bridge. You can place construction rods in it for structure strength, if you want. Keep this pad below grade. You do not want it higher than your bridge. I suggest making it a bit lower than ground level at it's location. You can always add a little ramp or some rock as you go on to your bridge.
Step 7. Add your decking. The simple way is to apply it perpendicular to the run of the bridge joists. If you do build the bridge 60 inches wide, you will be able to get 3 pieces of decking from each 16 foot length that you order.
Step 8. Place a small curb on the sides of your bridge. You can use a 2 by 4 or a 4 by 4 for this curb. It should be up at least 1 1/2 inches above the bridge surface.
Step 9. Paint a clear wood sealer on your bridge. This will give it an attractive appearance.
Tips; Use dry wall screws for your decking. Use bolts, when connecting your joists to your pier posts. since the pier posts will bear a lot of the weight, use two bolts for each post. If you have to connect your joists, use added braces with bolts to make it more secure. This depends on the length of your bridge. A small bridge won't need this step.
A ditch bridge can be an attractive and practical addition to your yard or garden.