It is 21x145mm overall Size. Featuring a modern premium fine planed finish, it is easy to install due to predetermined half-laps. Our slow grown Siberian Larch is one of the best available in the UK, carefully selected to ensure durability and denseness. If left to naturally to weather, this Larch will turn a beautiful silvery grey colour. Extra protection can be provided by applying a Larch exterior coating with UV protection.