What is the maximum percentage of glazing allowed in fire-protection-rated window assemblies relative to the common wall area?

In fire-protection-rated window assemblies, the maximum percentage of glazing allowed relative to the common wall area is 25%. This standard is established to balance safety and functionality in fire-resistant structures.

By permitting a maximum of 25% glazing, building codes aim to ensure that while natural light can be incorporated into spaces, fire performance and integrity of the wall are not compromised. Fire-rated assemblies are designed to resist flames and smoke, and a larger area of glazing could weaken this fire resistance.

This limit is also related to fire spread prevention, maintaining occupants' safety by minimizing the potential for combustion and allowing for proper egress in emergencies. The various percentages in the other options may not provide sufficient resistance or may be too restrictive for practical architectural design, thus the chosen 25% represents an acceptable compromise between visibility and safety within fire-protection-rated constructions.