Building timber is a type of construction material used in the building of structures. It is typically made from wood, and the most common types are OAK, ASH, and JOIST. OAK is a hardwood that is strong and durable, making it an ideal choice for building timber. ASH is also a hardwood, but it is lighter in weight than OAK, making it easier to work with. JOIST is a type of timber that is used to support floors and ceilings, and it is usually made from softwood. All three types of timber are essential components of any building project.