What is the effect of too many layers of roof coverings?

Having too many layers of roof coverings can lead to potential issues with rafter spread. When multiple layers of roofing materials are added, the weight on the underlying structure increases significantly. This additional weight can create stress on the rafters, which may cause them to spread apart, compromising the integrity of the roof structure.

Rafter spread occurs when the roof's lateral loads are not properly accounted for due to excessive layering, leading to a decreased ability to support the roof's weight. This can ultimately result in structural failures, sagging, or even collapse in severe cases.

In contrast, the other options present benefits that are generally not realized with excessive layering. For example, while insulation and energy efficiency may be attributes of a well-designed roof, simply adding more layers does not inherently improve these aspects and can, in fact, lead to problems like inadequate ventilation and moisture retention. Additionally, increased structural strength is not achieved through additional layers but rather through proper design and materials suited to the specific load requirements of the building.