Hills sometimes pose a challenge to building a fence, especially for town-dwellers erecting a privacy fence. While most forms of fence can be built on steep slopes by following the contours of the hill, the wall-like nature of a panel fence precludes this. Instead, one must use the stepped method, which adds a layer of calculation and work to fence-building. However, the job is otherwise similar to building a panel fence on level ground, so working on a slope remains a manageable do-it-yourself project if undertaken with care.
Drive a stake into the ground at the top and bottom of the slope where the fence line will go. Tie a string between the base of the top stake and the top of the bottom stake. Check the string with a level and adjust it for straightness. Because the string needs to be straight, the bottom stake needs to be tall enough to maintain a straight line.
Measure the distance between the string and the ground at the bottom stake. This is the drop in the slope.
Measure the distance between the two stakes with a measuring wheel. Divide this by the width of your fence panels to determine the number of panels that must be installed in that space. So, a 32-foot fence line with 8-foot panels requires four panels.
Determine the distance each fence panel must drop. A mild slope that drops 12 inches over 32 feet means each of those four 8-foot fence panels must drop 3 inches in succession to create an even, step-by-step appearance.
Walk along the fence line with a measuring wheel and plant a stake at intervals equal to the width of the fence panels to mark where the fence posts go. In this example, that distance is 8 feet.
Tie the string between the first and last stake in the fence line and look down the line to ensure the individual stakes are placed in a straight line. Move any stakes that are out of position.
Remove the stakes and excavate the post holes with a shovel and post hole digger. Dig the holes on level ground to a width equal to one-half the width of the posts and to a depth equal to one-third of their length. Dig those holes on the slope so that they are wider by 2 or 3 inches and shallower by an amount that compensates for the drop in height plus a margin of error (7 or 8 inches in this example).
Place a fence post into the post hole; check it by placing a level along the side and adjust it into a vertical position. Mix a batch of quick-setting concrete and fill the post hole up to about 3 or 4 inches from the top. After the concrete sets, fill in the rest of the hole with dirt.
Place a fence panel onto the first two posts in the line and check it with a level for straightness. The ends of the panel rails need to be set on the middle of the post. Attach the panel to the post by driving two nails into each of the rail ends. Repeat for each panel until you reach the slope.
Adjust the placement of the panels for the slope by stepping down each panel using the measurement determined in Section 1, Step 4. In this example, each of the four panels on the slope should remain level (i.e. not follow the slope at an angle) and attached to the posts in a position 3 inches lower than the panel before it, stepping down to follow the slope.
Cut off the tops of any fence posts that are too long with a chainsaw.
Digging the holes on the slope to a shallower depth is necessary to compensate for the drop in height while using fence posts of a uniform length, because more of the post needs to be above the ground. However, this weakens the rigidity of the fence post. This is compensated for by digging wider post holes on the slope, creating a bigger concrete base. For long slopes or steep slopes, you may find it necessary to determine the drop in height in stages.