What is the construction feature called in which there are vertical channels in the exterior walls from foundation to attic, allowing rapid, unchecked vertical fire spread?

The construction feature referred to in the question is known as balloon framing. In balloon frame construction, the wall studs extend continuously from the foundation to the roof, creating vertical channels that can facilitate rapid vertical fire spread through the open spaces within the walls. This design can allow fire to travel unchecked from the lower levels to the upper stories, posing significant safety hazards during a fire emergency.

Balloon framing is distinct in its use of long, continuous wood members, as opposed to being segmented into smaller sections at the floors, which would be characteristic of platform framing. The vertical channels that result from this continuous framing increase the potential for fire to spread quickly, making it a critical consideration for firefighters when assessing building hazards or planning for fire suppression strategies.

This understanding is vital for ensuring firefighter safety and effectiveness during operations in structures built with this type of framing.