21mm nominal thickness. 19mm finished size after machining. Almost double the finished thickness of normal 12mm thick cladding. Smooth planed and fully interlocking tongued and grooved boarding with the traditional and ever popular shiplap profile. The design ensures that rainwater drains quickly and the timber dries quickly. This helps to ensure a longer life for your building. Our buildings feature properly tongued and grooved boarding which is stronger than the half lap shiplap or rebated shiplap used by many others.