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Lap siding is a type of siding for buildings made from long, broad planks which are designed to overlap with each other. It looks similar to clapboard, and sometimes people use “lap” and “clapboard” interchangeably, although lap-style siding is technically larger than clapboard siding. This type of siding is suitable for a wide range of climates and can be seen on many different types of structures, from modern buildings to classic examples of traditional architecture.
A single piece of lap siding has a wedge-shaped profile when viewed from the side. The narrow end of the wedge goes up, nestling under the broad end of the wedge of an overlapping board. The overlapping boards together help to shed water, keeping water away from the interior of a structure and acting as a first line of defense against water intrusion. Lap siding is usually installed over a house wrap product, with plywood or similar materials being installed under the wrap, and the structural framing underneath these layers of material.
A variation on basic lap siding known as Dutch lap siding has a slightly different appearance. The boards are designed to overlap, but the angle of the bevel is steeper, creating a sharper visual appearance with troughs between each of the overlapping boards. Both regular and Dutch lap siding can be simulated with sheet siding products which mimic their appearance, but go on in a single piece instead of in layers.
While wood lap siding is traditional, it's also possible to find cement, vinyl, and engineered wood products such as HardiePlank® used for siding. These products can be more environmentally friendly because they are not made with virgin wood, and they can also be more durable than traditional wood siding products. Especially in extreme climates, using a non-wood siding product may actually be recommended for durability reasons. Manufacturers of products like vinyl lap siding have become quite talented when it comes to mimicking real wood, and many people can't tell the difference from a distance.
Sometimes a single board becomes damaged and needs to be replaced. On some structures, repairing siding is relatively easy to do, while in other instances, it may require the attention of an experienced contractor. When siding is removed for replacement, it's a good opportunity to inspect the underlying surface for signs of water intrusion such as mold, mildew, staining, and warping. If there are signs of damage, a contractor should be consulted about the next steps to take, and if the siding product has a warranty, it may be worth a warranty claim to see if the company will pay for repairs and replacement.