When we talk about Nominal vs Actual, we are referring to the size of materials. This is particularly relevant to structure, such as the timer/lumber sizes.
In North America one of the most common lumber sizes is 2×4. So, you would think that when you draw a wall with 2×4, that the dimensions would be 2″ by 4″. Right? Well this is where Nominal vs Actual comes into play. You see, 2×4’s are not actually 2″ by 4″. When the board is first rough sawn from the log, it is a true 2×4, but the drying process and planing of the board actually reduce it to a finished 1.5×3.5 size.
So, 1.5″ by 3.5″ is the Actual size of a 2×4 piece of lumber.
However, many Architects and Designers have chosen to simplify things by drawing the frame at 2″ by 4″ in their plans – or they have been incorrectly taught that the lumber size is actually 2″ by 4″. This is called Nominal sizing – and we think that this is a big mistake!