What is the minimum clearance between concrete or masonry chimney and combustible framing?

What is the minimum clearance between concrete or masonry chimney and combustible framing?

• A. 50 mm
• B. 100 mm
• C. 25 mm
• D. 75 mm

Answer: (A)

The main idea here is safety: heat from a chimney can ignite nearby combustible framing, so a guaranteed air gap is needed. For concrete or masonry chimneys, this minimum gap to any combustible material (measured from the outside of the chimney) is 50 mm (about 2 inches). This distance gives enough insulating air and reduces heat transfer to wood framing. If you see other distances like 25 mm, 75 mm, or 100 mm, they’re not the minimums for this type of chimney—they’re either not as safe as required or apply only in other situations or codes. Always verify with your local code, but the standard minimum here is 50 mm.

The main idea here is safety: heat from a chimney can ignite nearby combustible framing, so a guaranteed air gap is needed. For concrete or masonry chimneys, this minimum gap to any combustible material (measured from the outside of the chimney) is 50 mm (about 2 inches). This distance gives enough insulating air and reduces heat transfer to wood framing. If you see other distances like 25 mm, 75 mm, or 100 mm, they’re not the minimums for this type of chimney—they’re either not as safe as required or apply only in other situations or codes. Always verify with your local code, but the standard minimum here is 50 mm.