Final answer:
Valley rafters are the rafters that extend diagonally from the top plates to the ridge board at the intersection of two roofs, crucial for complex roof structures.
Step-by-step explanation:
The type of rafters that extend diagonally from the top plates to the ridge board along the lines where two roofs intersect are commonly referred to as valley rafters. These rafters are essential in the construction of complex roof structures where two roof planes come together at an angle, forming a valley. The design of such rafters often allows for the efficient shedding of water and the transfer of loads.
The construction of valley rafters aligns with traditional practices in architecture, such as in the sharply pitched roofs of long houses designed to manage snow loads, or the intricate timber roof construction, like those found in some Romanesque cathedral wooden ceilings or trussed rafter roofs.
The kind of rafters that extend diagonally from the top plates to the ridge board along the lines where two roofs intersect are called hip rafters.
Hip rafters are commonly used in roof construction to support the intersection of two sloping roof surfaces. They run diagonally from the corners of the top plates to the ridge board, forming a triangle shape that distributes the weight of the roof evenly.
For example, in a hip roof design where two roofs intersect at a corner, hip rafters would be used along the lines of intersection to provide structural support and ensure stability.