In Australian commercial construction projects, a header refers to a horizontal structural element that spans across the top of an opening, such as a door or window . It is a beam that disperses the structural load to the outside of the opening, providing support and stability to the surrounding structure .

In the context of bricklaying, a header can also refer to a brick laid with its short end to the face of the wall . However, in the context of commercial construction projects, the term "header" is more commonly used to describe the horizontal structural element above an opening.

Headers are typically built to rest on trimmers, also known as jacks, and are an essential component of a building's structural framework . They play a crucial role in distributing loads and ensuring the stability and integrity of the building.

It is worth noting that the National Construction Code Series (NCC) provides guidelines and standards for the design and construction of buildings in Australia, including the use of headers in commercial construction projects . However, the specific requirements for headers may vary depending on the project's location, size, and type.