How to Add a Lean-To on a Pole Barn

Determine the size of the lean-to. Purchase enough lumber to build the lean-to. The 2-by-4-inch posts outline the base and are used for roofing support. The 4-by-4-inch posts are used for the wall structure. Plywood is used for the walls and the roof. The lean-to can have zero to three walls (depending on your needs).

Measure the width of the lean-to from the outside edge of the pole barn. Mark the width with the marking paint, garden hose or string. Next, determine the length of the lean-to. Mark the length from the outside end of the first width marker with the marking materials. Add a line for the rear width from the end of the length marker to the pole barn.

Dig post holes for the 4-by-4-inch posts. The first 8-foot board is placed against the pole barn. The second one is placed at the meeting line of the width and length of the lean-to. If you want a sloped roof, sink the outside 4-by-4-inch posts a few inches deeper than the posts against the wall. Place a 4-by-4-inch post every 24 inches along the length of the lean-to. If you want a taller lean-to, use 10-foot posts, for a shorter lean-to, use 6-foot posts.

Center the 4-by-4-inch posts in the holes. Use rocks, broken cinder blocks or dirt at the bottom of the hole to hold the post upright. Fill the rest of the hole with cement. Allow the cement to dry according to the instructions on the package or, if no time is specified, for at least 24 hours.

Screw 2-by-4-inch boards to the bottom of the posts to form a barrier, or base, along the ground. You may have to dig out the ground in some areas so that the 2-by-4-inch boards are level. They should be flush with the ground in all areas. The boards help contain the gravel for the floor.

Screw a 2-by-4-inch post to the pole barn between the two end 4-by-4-inch posts. Make sure this board is level all the way across, as it holds the plywood for the roof. Screw another 2-by-4-inch post to the front of the outside posts. Attach the L brackets every 24 to 36 inches for added support. On the front, use the L brackets at the posts and the 2-by-4-inch post to give more support.

Screw 2-by-4-inch posts to the 4-by-4-inch posts, running perpendicular. These form the supports for the roof. Use L brackets to add extra support.

Screw the plywood to the roof trusses (added in Step 7). If the lean-to will have walls, screw them to the plywood.

Line the plywood on the roof with the tarp paper. Tack it on with roofing nails (use just enough to keep the paper on). Also tack tarp paper to the walls. Tarp paper always goes on the exterior̵2;it protects the wood from the elements.

Add shingles. Start at the outside edge of the roof, laying shingles down the length of the lean-to. Work up towards the pole barn, overlapping the shingles and nailing each one down with roofing nails. Line the edge of the aluminum flashing with caulk. Screw the aluminum flashing to the side of the pole barn, bending it along the crack between the plywood and the pole barn. Screw the bottom edge of the aluminum flashing over the top of the shingles.

Apply the siding to the walls. Follow the instructions that come with the type of siding you purchase. Pour and spread gravel on the floor inside the lean-to. For maximum effectiveness, use at least 2 inches of gravel.