Tongue-and-groove and shiplap are siding "profiles." The term profile describes the unique shape that results from milling or manufacturing siding planks. The differences between tongue-and-groove and shiplap are both functional and aesthetic. They not only have unique installation requirements and weathering characteristics, but also create distinct visual patterns. A comparison of tongue and groove helps you choose the type of cladding that fits both design and budget.
Whereas adjacent tongue-and-groove planks interlock, adjacent shiplap planks overlap. Tongue-and-groove planks consist of a channel on one edge, called a groove, and a corresponding lip on the opposite edge, called a tongue. The tongue precisely fits into the groove, so that builders literally stack groove over tongue to interlock the planks. While the groove of a tongue-and-groove plank runs through the center of a plank's edge, the groove of a shiplap plank cuts in from the face of the plank to form a step-like cut. The top groove of a shiplap plank cuts in from front face of the plank and the bottom groove from the rear face of the plank. Thus, the bottom groove of each shiplap plank nests within the top groove of a lower plank.
In general, installing tongue-and-groove siding requires more work than installing shiplap siding. In standard installations, tongue-and-groove planks are nailed at an angle through the each plank's tongue and into wall sheathing or framing. Nailing through the tongue increases strength and conceals the fasteners within the joint between adjacent planks. On the other hand, most shiplap installations simply require nailing straight through the face of the overlapping planks.
Although both tongue-and-groove and shiplap are suitable for exterior applications, shiplap tends to shed water more effectively than tongue-and-groove. Water often becomes trapped within the interlocking tongue-and-groove and leads to rot or deterioration. The step-like shape of shiplap planks often slopes downward and away from the wall to facilitate drainage.
Wood is the most common materials for both tongue-and-groove siding and shiplap siding. Manufacturers typically produce siding planks from naturally weather-resistance wood species, such as cedar and redwood. Alternatively, manufacturers produce tongue-and-groove and shiplap imitations from a broad range of materials, including metal, vinyl and fiber-cement. While metal, vinyl and fiber-cement siding planks often resemble the appearance of tongue-and-groove or shiplap, they overlap or interlock by unique, sometimes proprietary, installation systems.