What are Diagnostic Cuts used for?

• A. To speed up the roof opening
• B. To mark the edges of the decking
• C. To measure air flow
• D. Used to determine roof construction and fire conditions

Answer: (D)

Diagnostic cuts are used to quickly learn what the roof is built like and what the fire is doing inside. By making a few shallow cuts in the roof surface, you can see how the rafters or joists run, whether there are multiple layers or a void above the fire, and if the cockloft is involved. This information is crucial for planning vertical ventilation safely and effectively, because it tells you where a proper opening will help exhaust heat and smoke without compromising the structure. They aren’t about marking edges or measuring air flow, and they don’t primarily serve to speed up the opening—their purpose is to reveal roof construction and fire conditions so ventilation decisions are informed.