Fireplace Clearance to Combustibles and Mantel Projection (IRC R1001.11)
Whether the wood around a masonry fireplace keeps its distance under IRC 2024 R1001.11.
Example
You enter
- Framing clearance at the front faces and sides (in, blank to skip) 2
- Framing clearance at the back face (in, blank to skip) 4
- Fireplace opening area under_6
- Sheathing or trim abutting the sidewall: distance from the firebox lining (in, blank to skip) 8
- Mantel or front trim: distance from the opening (in, blank to skip) 9
- Mantel or front trim: projection from the masonry face (in) 1.5
You get
- Mantel projection allowed at its distance 1.125 in
- Distance its projection needs 12.00 in from the opening
- Checks failed 1
- Checks run 4
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeFraming stays 2 in off the front faces and sides and 4 in off the back, and the gap stays empty. Siding, flooring and drywall edges may butt the sidewalls and hearth extension only 8 in or more from the inside of the firebox lining, or 12 in for an opening of 6 sq ft or more (IRC 2021 asks 12 in for every opening; pick the edition). A mantel or trim on the fireplace front stays out of the 6 in around the opening, and within 12 in of it may project only 1/8 in per inch of distance: 1 in proud at 8 in, 1.5 in at 12 in. A 1.5 in mantel shelf 9 in above the opening is allowed 1.125 in and fails; it needs 12 in. It reports the projection allowed at the mantel's distance and the distance its projection needs. Listed fireplaces, fireplaces built into masonry walls, factory-built fireplaces and stoves have their own rules.
Formula or tableframing >= 2 in at the front faces and sides, >= 4 in at the back; sheathing edge or trim abutting the sidewall >= 8 in from the firebox lining (>= 12 in for an opening of 6 sq ft or more, and for every opening under IRC 2021); mantel or trim on the front: none within 6 in of the opening, projection <= distance / 8 within 12 in (inclusive), no limit beyond 12 in; distance needed = max(6, 8 x projection) for a projection up to 1.5 in.
Source and editionIRC 2024 (International Residential Code). Section R1001.11 and its Exceptions 1 to 4, read at codes.iccsafe.org on 2026-10-19; IRC 2021 R1001.11 read there on 2026-10-20, whose Exception 3 is 12 in for every opening (the 8 in case is new in 2024).
Free accessFree to read at codes.iccsafe.org.
What governsEstimate. AHJ and licensed structural engineer govern.
API field namesframing_front_in, framing_back_in, opening_area_class, sheathing_from_lining_in, mantel_distance_in, mantel_projection_in, allowed_projection_in, distance_needed_in, checks_failed, checks_run
- Exactly 12 in is within 12 in a 1.5 in projection is allowed at 12 in; thicker needs more than 12 inreading of R1001.11 Exception 4
- Masonry fireplace factory-built fireplaces, inserts and stoves follow their listingsIRC R1004