You've probably seen them when driving through your neighborhood or visiting friends: wooden fences that sag in the middle even though they're only a few years old. If you're getting a new wooden fence, then it's important to take steps to ensure it does not start sagging. Here's what you need to do:
Make sure the posts are set in concrete
Ideally, each fence post should be set in a concrete "foot" to prevent it from bending to the side or sinking further down in the soil. Some homeowners skip this step because they're trying to save time or money, but it will only end up costing you more in the long run when you have to fix a sagging fence. Some fence contractors may give you the option of having your posts set in gravel rather than in concrete. This can work okay in clay soil that you're confident won't compact or shift, but you're still making a gamble. You're better off spending a little more on concrete and being absolutely confident you won't have to deal with settling posts.
Make sure you give the concrete adequate time to set before mounting any rails to the fence posts. If you put them on too soon, the weight of the rails may push some of the posts too far down, leading to a crooked fence.
Use long screws to attach the fence rails
Whether you have a post-and-rail fence or a solid privacy fence, make sure you use long, 1 ½-inch or 2-inch screws to attach the fence posts. (Or check that this is the technique your contractor uses.) Using nails is quite common, but it can result in boards that begin slumping downward if the nails begin to bend or shift downward in the wood.
Use several screws for each fence rail
A single screw may hold the rail in place for now, but it may eventually work its way down in the wood, allowing your fence rail to shift and sag. Use at least two screws in each side of the fence rail. Three is even better and is ideal if you have wide, 6 or 8-inch fence rails.
Hiring a reputable fence company will go a long way towards keeping your fence from sagging. Ask for references from previous customers. If their fences are a few years old and are not sagging, you can be pretty sure yours won't either.
For more information about fence installation, contact your local fence contractor.