Firebox walls are solid or solid-grouted masonry, stone or concrete: 8 in total at back and sides with at least a 2 in firebrick lining (joints 1/4 in max), or 10 in with no lining.
Steel outlet boxes up to 16 sq in may pierce a rated wall's membrane if they total no more than 100 sq in per 100 sq ft, gaps are 1/8 in or less, and opposite boxes are 24 in apart or otherwise protected.
An unsprinklered house's exterior walls closer than 5 ft to the lot line need a 1-hour rating, tested from both sides.
Unsprinklered: no projections within 2 ft of the line; 1-hour underside from 2 to under 5 ft; unrated at 5 ft or more.
Unsprinklered: no wall openings within 3 ft; up to 25% of the wall at 3 ft to under 5 ft; unlimited at 5 ft or more.
Penetrations within 3 ft of the lot line are protected per R302.4.
A fully sprinklered house only needs rated walls (tested from outside) under 3 ft; openings are unlimited from 3 ft and projections can be rated from 2 ft.
In a fully sprinklered subdivision, the separation distance can drop to 0 ft where the neighbouring lot keeps an open yard of 6 ft or more.
Two homes on one lot measure to an imaginary line between them; townhouses measure to the lot line or an imaginary line.
Exempt: walls perpendicular to the line, the owner's own accessory buildings, permit-exempt sheds, and foundation vents. A detached garage within 2 ft of the line may have eaves of up to 4 in.
Searches all 4,276 IRC 2024 sections, 5,532 IBC 2024 sections and defined terms (Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 so far) and each city's local rules as they are added. Section numbers and titles from the International Residential Code and International Building Code, 2024 editions, copyrighted by the International Code Council; the IRC's electrical chapters (34 to 43) follow NFPA 70, the National Electrical Code. Requirements are summarized in our words (IRC Chapters 3 to 43, IBC Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33); read the full text at the link on each result. Local values come from each city's published documents.
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