The key to an attractive, long-lasting fence is a row of sturdy fence posts, securely anchored and properly aligned and spaced. Posts are the working members of a fence, serving to bear and brace the gates and railings.
There is a wide range of fence post materials, as shown in the box opposite. Before setting any posts, check your property line and local zoning or building codes, which may determine fence height or setback from the street.
To help protect the top of a fence from rain, cut the post at a 30-to 45-degree angle before setting it, or cover it with a plastic or metal post cap, available at home centers to fit standard post sizes.
As a general rule, one-third of the post should be below ground. In relatively stable soil, tamped earth or gravel will hold the post securely. Gateposts as well as the end and corner posts, which are subjected to greater stress, should be set in concrete wherever possible. If you prefer not to go to the trouble and expense of using concrete, use longer lengths of lumber for these key posts and sink them deeper into the ground.
Avoid leaving holes unattended; set a post in its hole as soon as possible or at least mark the hazard by inserting the post or a tall stake.
Wear gloves when handling pressure-treated lumber; add a dust mask when cutting it.
As freezing water expands under and around posts, it tends to force them up. One solution is to sink the post below the frost line, which varies from region to region. It is generally impractical to sink posts deeper than 3 to 3½ feet. In this case, set the post in concrete; nails partly driven into the post help to hold it to the concrete. For added stability first widen the hole at the base into a bell shape so the surrounding earth holds the concrete in place.
Whether or not you use concrete, always set the base of the post in 6 inches of gravel. The improved drainage reduces the risks of frost heaves and prevents the post bottom from resting in groundwater and rotting. Four ways to set a post are shown on page 192.
Pressure-treated lumber is one of the most popular choices for fence posts, and with good reason: They are strong, widely available, and last at least 20 years. But there are other sound options. Naturally resistant woods like redwood, red and white cedar, and locust are all good choices if they are available for a good price in your area. They are commonly used for rustic-style fences. PVC posts, although more costly than wood, are attractive and typically guaranteed to last a lifetime.
Most wood fences are best supported by posts no smaller than 4-by-4s, but low picket fences can be anchored with 2-by-4 posts. All corner and gateposts should be 4-by-4s or larger.
Locating posts on flat ground
Drive stakes at the locations of the end posts and stretch a mason’s line between them. Measure the distance between the posts and determine the standard lengths of lumber or fencing that will make up the rails of the fence with a minimum of cutting. In general, posts are spaced a maximum of 8 feet apart; this way, a 16-foot length of lumber will span three posts. Make a gauge pole by cutting a straight 1 -by-2 board to the length of the fence sections. Lay out the post positions with stakes as shown at left. Adjust the intervals for gateposts and to avoid ending the fence with a very short section.
Staking posts on uneven ground
For a fence with a level top, stretch a mason’s line between two end stakes and level it with a line level. With a helper measuring along the line with a gauge pole, drop a plumb bob from the line to pinpoint each post location on the ground (above). Drive a stake at each one. For a fence that follows the contours of the ground, drive stakes at the fence ends and at each high and low point in between. Join all the stakes with a mason’s line and position the stakes for the remaining posts evenly along the line as shown above.
This simple method has been used to lay out right angles for centuries. Drive stakes to establish your first fence line, with one stake at the desired comer point. Attach a mason’s line to these two stakes, then tie a marker string to the line at the 3-foot mark. Stretch another line from the corner stake, roughly perpendicular to the first line and secure it to a batter board—a horizontal board nailed to two stakes. Tie a marker string to this line at the 4-foot mark. Slide this line along the batter board so that the distance between the two marker strings is 5 feet (right). The angle between the two lines will be 90 degrees.
Burrowing a hole with a posthole digger
Untie the mason’s line from the stakes, putting it aside for aligning the posts (page 191). Start the hole by cutting out a circle of sod around the stake with a spade. Dig out the posthole with a clamshell posthole digger, as shown. For very sandy or heavy clay soils, a digger like the one shown in the photograph works best. A post set in concrete requires a hole three times the post width; for one to be set in tamped earth make the hole twice the post width. If the frost line is deeper than 3 feet angle the digger to widen the bottom (above). Extend the hole 6 inches deeper than needed and pour in 6 inches of gravel.
If you are setting 10 or more fence posts, consider renting a power auger. Unless you are working in very rocky or very heavy clay soils it saves both time and effort. The two-person auger above is less likely to kick out of the hole when it hits a rock than the one-person version.
To use a power auger, mark the posthole depth on the bit with tape and set the machine over the marked position. Start the motor and adjust the speed with the handle-mounted throttle. Guide the machine as the bit pulls it into the ground. After digging 8 to 12 inches, raise the bit to clear the dirt from the hole. If you hit a rock, pry it loose with a digging bar or pick and shovel.
Bracing an end or corner post
Drive two stakes on adjacent sides of the posthole. Fasten a 1-by-2-inch bracing board to each stake with a single 1½-inch common nail. Center a post in the hole and use a carpenter’s level to plumb one side of the post (left); alternatively, use a special post level (photograph), which will enable you to plumb both directions at once. Nail the first brace to the post, then check for plumb on the other side and secure the second brace.
Aligning intermediate posts
Attach two lines to the end posts, one near the top and the other close to ground level. For the upper line, make sure that it is attached at exactly the same distance from the top of the posts. Place an intermediate post in a hole. Add or remove gravel to set the post at the correct height according to the alignment line. Have a helper align one side of the intermediate post with the two lines, then plumb an adjacent side with a level. Sight along the top line to check both the post height and the alignment (right); alter alignment by shifting the post base.
There is no one correct way to secure a fence post. Soil type, intended use, climate, and budget all influence the selection of fillers. The one ingredient common to all methods is a 6-inch base of gravel. This will help prevent water from pooling around the post bottom where it will be drawn into the end grain and hasten decay.
The simplest method is to replace and tamp the soil that was removed to make the hole. This works well if the fence is less than 4 feet high and sitting in well-drained soil, which reduces the risk of frost heave.
There are two practical reasons to bolster a post with concrete: strength and protection from frost heave. If additional strength is needed but frost heave is not a significant threat, then fill the hole halfway with tamped soil and top it with concrete, for a partial concrete collar. If the post only requires protection against frost heave, then pour enough concrete to fill the bottom 8 to 12 inches of the hole, driving nails partway into the post to anchor it to the concrete.
A full concrete collar, extending from the drainage gravel to just above the ground, is definitely the strongest method of setting a post. It protects against frost heave and will render a post strong enough to hang a gate or hold a tall fence.
Securing a post in tamped earth
While a helper holds the post plumb and touching the alignment lines (page 29) fill the hole with earth in 3- to 4-inch layers, tamping as you go with the flat end of a tamping bar or a 2-by-4. Make sure you do not inadvertently shift the position of the post. If you are using only soil, overfill the hole and shape a slope of earth around the post to shed runoff. If you are topping the hole with concrete, simply fill the hole to the appropriate height with tamped earth, leaving room for the concrete (opposite).
Unmilled round posts of cedar, locust, or redwood are often curved at their large end. To allow for this, dig the hole to the correct depth; then shape one side to match the curve on the post, allowing the above-ground part of the post to stand plumb. Finally, dig the hole 6 inches deeper, then add 6 inches of gravel for drainage. When the earth is tamped back in place the post will be directly braced against undisturbed soil, providing a secure support.
Setting a post in concrete
Ensure that the post is aligned and plumb. Prepare a batch of premixed concrete with a square-edged spade according to the manufacturer’s directions, then fill the hole. Agitate the concrete with the shovel to remove any air pockets, but be careful not to knock the post out of position. Overfill the hole slightly and use a mason’s trowel to slope the concrete down from the post to improve runoff. Allow the concrete to set for 48 hours before removing the braces or attaching the fencing. If you are only laying down a concrete anchor, pour in about 8 to 12 inches of concrete; usually this amounts to one bag of pre-mixed concrete for each post.