Final answer:
Adequate knee walls are designed to support and stabilize the rafters and would not cause rafter spread, unlike the other options listed, which could potentially lead to structural issues.
Step-by-step explanation:
The phenomenon of rafter spread refers to the situation where the rafters of a roof push outward at their base, potentially causing structural weakness or failure. Rafter spread can have various causes, including too many layers of roof coverings, lack of collar ties, or over-spanned rafters. However, adequate knee walls would not cause rafter spread since they are intended to support and stabilize the rafters, preventing the outward movement that characterizes rafter spread. Understanding and preventing rafter spread is crucial as during historical periods significant buildings with wall systems and open roofing needed strong load-bearing walls to prevent collapse. Large roof spans can push walls outward, so the walls must be designed to accommodate only the necessary openings, like windows or doorways, without compromising structural integrity.