Erecting a fence becomes more complicated when the ground has a steep slope. Stepped fences tend to leave a large amount of space under the bottom rail as the ground slopes away from the bottom rail. If you are installing pickets or slats, you can usually extend them below the rail to meet the ground. When installing fixed panels, though, you may need extra panelling to fill in the space. If you are making a picket or slat fence, you can avoid this problem by running the rails parallel to the slope.
Set a fence post on the highest point of the slope. You should dig each post into the earth so that one-third of the total length is buried. This means that if you are building a 6-foot fence, you should dig a hole 3 feet deep with a posthole digger and use posts that are 9 feet long. It will save you measuring time to use a 10-foot post and cut off the top when you attach the rails.
Measure the distance from the ground to the position of the top rail with a tape measure and mark this distance on the post with a pencil. Stretch a line level to the position of one of the adjacent posts and measure the distance from the line to the ground to give you the minimum length you need for the next post. Dig a hole and set a post of appropriate length.
Set all the posts around the perimeter of the fence in the same way, being sure to set two gate posts spaced the same distance apart as the width of the gate you plan to use.
Connect the posts with top rails, starting at the post on highest ground and working around the perimeter. Mark the height on the first post and use the line level to mark the position on an adjacent post that is at the same level. Attach the rails with screws or corner brackets. Set the bottom rails in the same way, making the mark on the first post about 4 inches off the ground.
Screw slats or pickets to the rails, using a level to make sure that each one is vertical and that the tops are at the same level. Lengthen the slats or pickets progressively to follow the slope, keeping the bottoms 1 or 2 inches off the ground.
Attach panels by marking the position of the top rail on the first post, stretching the line level to an adjacent post and making a corresponding mark. Connect the panels to the posts with screws or corner brackets.
Cut a piece of panelling to attach to the bottom rail that will fill in the gap between the rail and the ground. The shape of this piece will be roughly triangular. Shape the bottom with a jigsaw.
Set all the posts around the perimeter of the fence at the same time. They should all be the same height.
Mark the positions of the top and bottom rails on all posts in the same way, measuring from the ground to the same height on each one.
Affix the rails to the posts on the marks. You may have to cut angles in the ends of the rails with a circular saw. These angles do not have to be exact, but the more accurate they are, the better the fence will look.
Set each picket or slat the same distance from the ground and screw it to the rails, using a level to plumb it.
Metal fencing kits are usually adjustable so you can run the fencing parallel to the slope. All the posts on metal fences are usually the same height. Some manufacturers of wood panels make them rackable so you can adjust them to a slope.
Leave a gap between the bottom of wood fence slats and the ground. If they are touching the ground, the bottoms will rot.