Final answer:
A horizontal tie that connects opposite pairs of rafters to help stiffen the roof is called a collar tie. It is part of the roof's structural framework and necessary for resisting the outward force applied by rafters, thus essential for the stability and safety of a building's roof structure.
Step-by-step explanation:
A horizontal tie that connects opposite pairs of rafters to help stiffen the roof structure is commonly known as a collar tie. Collar ties are typically installed in the upper third of the attic space and are essential in preventing the roof from spreading under heavy loads, such as snow or wind. They are part of the roof's structural framework and work by providing resistance to the outward force that the rafters exert on the walls.
Installing collar ties can be a critical aspect of framing a roof since they ensure that the roof remains stable and can support any additional weight without the walls being pushed outwards. In most homes, you will find these ties made from wooden beams, and they are usually positioned horizontally between opposing rafters. The correct placement and installation of collar ties contribute significantly to the overall durability and safety of a building.
Collar ties are not only functional but can also add to the aesthetic appeal of a home, especially in cases where the rafters and the ties are left exposed in the design of the interior space, giving a rustic or industrial look. When designing a roof, engineers and builders must take collar ties into account to ensure that the roof meets building codes and performs well throughout its service life.