For most types of fences, hills pose few problems, as the wires or rails can easily follow the contours of the hill slopes. However, panel fences can never follow the contours of a hill and retain a neat, orderly appearance. This style of fencing, which includes most privacy and picket fences, must be stepped up and down the slopes of the hill. The process of putting the fence up is similar to a normal installation, but involves some complicated calculations.
Look up the length of the panels in the fence, which should be on the delivery papers or invoice. If not, measure the length with a tape measure. Each panel should meet and be fastened to the middle of a given fence post.
Establish the fence line by walking in a line where you want to install the fence and driving stakes into the ground at intervals set by the length of the fence panels. Tie a line of twine between the first and last stake and check for straightness. Pull up and reset any stakes that are out of alignment.
Drive an extra pair of stakes, one at the top of the hill and one at the bottom, marked with coloured cloths or a marker to distinguish them from the other stakes. Tie twine to the bottom of the stake at the top of the hill and to the stake at the bottom of the hill, and then adjust the string along the bottom stake so it is horizontally straight. Once you've checked the twine with a level, measure the distance from the string to the ground on the lower stake to determine the drop in the hill slope. Note that this means the bottom stake may need to be much longer than the others, or you may need to take this measurement in stages.
Measure the distance between the two special hill stakes with the measuring wheel. Use this distance to establish how many fence panels you'll need to cover the distance (a 40-foot long slope with eight-foot panels needs five panels).
Calculate how much each successive panel must step up or down the slope by dividing the drop of the slope by the number of fence panels. A five-foot drop with five panels means every fence panel will step up or down by one foot.
Dig post holes. The typical hole for a line post should be as deep as one-third the length of the posts and twice as wide. However, the fence posts on the slope need extra height to manage the steps. In this example, it would be 14 or 15 inches for the 12-inch step, to establish a margin for error. This demands either a taller post or a shallower post hole. If you do not have the necessary longer posts, subtract the extra height from the depth of the post holes for those holes dug on the hill slope.
Set line posts in ordinary ground in compacted earth. Plant the post into the post hole and set it in a vertically straight position using a level. Shovel in enough dirt to fill one-quarter to one-third of the hole and tamp that dirt down with a tamping rod. Continue shovelling in dirt and tamping it down until the post hole is full of solid, compacted earth.
Set gate posts and posts on the hill slope in concrete instead of dirt. Gate posts bear more weight and the posts on the hill slope are probably in shallower holes, so both need the extra strength provided by a concrete plug. If you have extra-long fence posts, set only the gate posts in concrete. Mix quick-setting concrete and pour it into the hole while holding the post in a vertically straight position. Once the concrete sets, release the post.
Install fence panels along the level sections of the fence by nailing the panels to the midpoint of the fence posts. Each panel has a rail at the top and bottom. Use two nails per rail.
Fasten the fence panels to the posts on the hill slope by raising or lowering each panel by the stepping distance (in this case, 12 inches) relative to the panel before it. Otherwise, nail the panel rails to the fence post as in Step 9.
Look at the fence line for uneven fence post tops, especially along the hill slope. Cut off the tops any extra-tall posts with a chainsaw to create an even appearance.
The task of setting fence posts, either in dirt or concrete, is greatly simplified with an extra pair of hands. If you do not have a helper, improvise a tripod at the base of the fence post by nailing scrap timber to it.