Houses built with wood will place the wood at regular intervals. Walls are usually built with the boards at 16 inch intervals while floors are usually 12 inches

Houses built with wood will place the wood at regular intervals. Walls are usually built with the boards at 16 inch intervals while floors are usually 12 inches and roofs may be 12 inch or 24 depending on loading conditions. In order to be able to type a house you need to know the multiples of 12 and 16 up to about 30 or 50 x 12.