Final answer:
Collar ties are used to stabilize roof rafters and must be installed on every third rafter to ensure a strong and stable roof structure as per building codes and standard construction practices.
Step-by-step explanation:
When constructing a roof, collar ties are a crucial component for providing structural stability. These ties are used to keep the rafters in place, preventing them from spreading apart under the weight of the roof or under heavy winds. According to building codes and standard construction practices, collar ties should be installed on every third rafter. This provides a balanced approach to ensuring a strong and stable roof structure without overconstruction, as utilizing ties on every other rafter may be overkill and not as cost-effective, and every fourth or fifth may not provide adequate support.