Residential Building Inspector B1Public Safety and Special ConstructionHard
A residential dwelling has a solid-fuel-burning fireplace. What is the minimum required thickness for the hearth extension when the fireplace opening is 6 square feet (0.56 m²) or less?
- A2 inches (51 mm)
- B4 inches (102 mm)
- C6 inches (152 mm)
- D8 inches (203 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 4 inches (102 mm)
For fireplaces with an opening of 6 square feet (0.56 m²) or less, the hearth extension must have a minimum thickness of 4 inches (102 mm). This thickness provides sufficient thermal protection for combustible floor materials beneath.
Why the other options are wrong
- A. This thickness is only permitted for hearth extensions when the fireplace opening is less than 6 sq ft, and only if constructed of specific noncombustible materials.
- C. This is not a standard minimum thickness for hearth extensions.
- D. This thickness is typically required for larger fireplace openings (greater than 6 sq ft).
Hearth Extension Thickness (Small Fireplace)
The minimum thickness for the noncombustible hearth extension in front of a solid-fuel-burning fireplace with a smaller opening.
- Applies to fireplace openings ≤ 6 sq ft
- Minimum 4 inches (102 mm) thick
- Protects combustible floor from heat and embers
Memory trick: Small fire, four inches wide, keeps the floor safe inside.