Fiber cement siding is a popular choice for homes because of its incredible durability. It's a mixture of wood pulp and cement that's compressed and formed into boards, and the manufacturing process allows it to fit in to any exterior design style you desire. It can be brushed and dyed during the manufacturing process to make it look just like wood, allowing it to be used for a rustic look, or it can be left untextured for a more modern design aesthetic.

One of the downsides of fiber cement siding, unfortunately, is that the boards are prone to warping and becoming wavy. If you have fiber cement siding on your home that looks lumpy and wavy, read on to find out more about what can cause it and how you can fix it.

Improper Installation

Fiber cement siding is tricky to install. The fiber cement boards are extremely heavy due to the cement content, so they need to be nailed directly to the wall studs of your home's framing in order to have adequate support. If the contractor who installed your siding wasn't familiar with how to install it correctly, they may have set the pressure setting in their nail gun too high in order to punch those nails through the boards.

Using too much pressure will immediately warp the fiber cement boards and cause them to appear wavy after installation. They're durable, but they're also fairly thin, and they can't hold up to a high-pressure nail being fired into them to secure them to a wall stud.

Soil Shifting

On the other hand, the installer may have done a perfect job. The waviness of your fiber cement may be due to the soil shifting underneath your home. This sometimes happens in new constructions as your home settles. When your home settles it can shift your home's frame, and this can bring where the nails are located in the wall studs out of parallel. Once that happens, the fiber cement boards will start to warp since the nails are no longer perfectly aligned.

Moisture Intrusion

If there's moisture getting behind the fiber cement boards, it can cause your exterior sheathing to warp. It's made of wood, so it will expand when it gets wet and contract as it dries out. This is another way that your wall studs can get out of alignment — moisture intruding through a hole in the fiber cement boards when it rains can leak onto the sheathing, causing it to expand while the adjacent areas remain dry. This will pull the boards out of alignment and cause them to appear wavy.

All of these problems can be fixed in the same way — call a siding contractor who has experience working with fiber cement and have it reinstalled. Moisture intrusion can be solved by adding more flashing to prevent it, and the boards can be realigned to make them straight if your wall studs shifted due to your home settling. If the waviness was caused by improper installation, they can cut the boards to salvage the undamaged areas while adding new boards to eliminate the waviness.