Before you alter an unreinforced masonry chimney in Seattle

Unreinforced masonry — URM for short — is brick or block laid up in mortar with nothing else in it. No steel bars run up through the middle, and no straps tie it back to the house frame. It stands on its own weight and the grip of its joints, which is plenty for holding itself up and very little else.

On a wood-frame house, that description usually fits exactly one element: the chimney. Everything around it is nailed and sheathed timber that can flex. The chimney is a rigid, heavy column standing clear of anything holding it, and it is the tallest thing on the building.

An unreinforced masonry chimney

Brick laid in mortar with no vertical reinforcing steel and no seismic anchorage to the framing. That describes most chimneys on older Seattle houses: roughly one housing unit in five in the city was built in 1939 or earlier.

A URM building

Something different, and worth separating out. SDCI's Unreinforced Masonry Retrofit Program covers buildings with one or more loadbearing walls of unreinforced masonry, generally built before 1945, and its retrofit standard is currently voluntary. A wood-frame house with a brick chimney is not in that program.

Height, weight, and weak connections. The Background section of SDCI Director's Rule 07-2025 gives those three as the reasons unreinforced masonry chimneys are extremely vulnerable to earthquake damage, and states that they may collapse during even a minor earthquake, creating a serious safety risk to occupants and to people below.

None of this makes a standing unreinforced chimney illegal. Seattle is assigned Seismic Design Category D2 in the residential code, and that is what triggers the reinforcing and anchorage provisions: vertical bars anchored into the foundation, ties enclosing that steel, straps into the framing. Those provisions are written for chimneys being built or rebuilt. Doing work on the chimney is what changes the picture.

Two triggers, both in the Seattle Residential Code. Section R107.5.3 states that if a URM chimney is altered, or if the building containing it undergoes a substantial alteration, the chimney must be altered to conform to rules promulgated by the building official. Those rules are SDCI Director's Rule 07-2025, effective January 8, 2026, superseding the 2004 rule much older advice still points at.

The second trigger is the one people miss. The code defines substantial alterations to include repair of buildings with damage ratios of 60 percent or more, and remodeling or additions that substantially extend a building's useful life. A remodel that never mentions the chimney can still bring it into scope, and whether a project qualifies is the building official's determination.

• A permit is the default. The Director's Rule requires a building permit for unreinforced masonry chimney work, with fees based on the value of construction.
• The exceptions are narrow. Two only: minor patching, and work under the low construction-value threshold the residential code sets for minor repairs in any six-month period. Neither is a general exemption for chimney repair.
• Unpermitted work still has to meet the rule. The rule states that all work must conform to it even where no permit was taken out, and being exempt from a permit never authorizes work that violates the code.

The code also treats a badly deteriorated chimney as a defined condition. Section R107.5.7 classes chimneys and similar appendages in deteriorated condition as unsafe building appendages, declares them public nuisances, and requires abatement. That determination belongs to SDCI.

The rule sets out three routes: an engineered design by a registered design professional; a prescriptive design from Part B of the rule, available for chimneys less than 12 feet tall above the roof line; or removal of the chimney. A taller chimney can sometimes be reduced in height to reach the prescriptive path; otherwise it needs an engineered design.

One requirement sits above all three routes. Alterations and repairs must be constructed in reinforced masonry, or the chimney replaced with a factory-built metal chimney. The single exception is repair limited to the top two feet, which the rule counts as minor patching; it does not extend to alterations or to substantial alteration projects. Rebuilding like for like in unreinforced brick is not the default answer any more.

1. Demolish to the floor line below the roof and rebuild upward in reinforced masonry, tied at roof and floor.
2. Demolish to the top of the smoke chamber and rebuild in reinforced masonry, tied at the roof and any floor line.
3. Demolish to just below the roof line, rebuild in reinforced masonry, tie at the roof line, and add an external brace where the chimney stands more than 3 feet above the roof.
4. Demolish to the top of the smoke chamber and install a listed metal transition assembly with a factory-built metal chimney above it.
5. Demolish to the roof line or lower, cap the chimney, discontinue its use, and strap it to the building.

Two general requirements attach to all five. A chimney extending more than 3 feet above the lowest adjacent portion of roof must be braced back to the building at a minimum of two points. And any existing unreinforced masonry left in place must be evaluated for damage or deterioration and its joints pointed up where needed.

Seattle has eight designated historic districts, among them the Ballard Avenue and Columbia City Landmark Districts, Harvard-Belmont, and the Pioneer Square Preservation District. Changes within them require a Certificate of Approval from a district board or the Landmarks Preservation Board — a separate review from the building permit, on its own schedule. A height reduction or a switch to a factory-built metal chimney alters the exterior, so find out early whether your address is affected.

Director's Rule 07-2025 is a City of Seattle code interpretation, and it carries no weight one block past the city limits. King County alone lists 39 incorporated cities and towns, each with its own municipal government and its own permit desk.

• Inside a city. Bellevue's Development Services Department, Kirkland's Development Services, Redmond's Development Services Center, the Issaquah and Bothell permit centers, Renton's Permit Services, Shoreline's Planning & Community Development department, Everett Permit Services, and Tacoma's Planning and Development Services.
• Outside city limits. Unincorporated areas are permitted by King County's Department of Local Services Permitting Division, by Snohomish County Planning and Development Services, or under Pierce County's own code — not by the nearest city.

The seismic design category is not what makes Seattle different; Renton, for one, adopts Seismic Design Category D2 in its own amendments to the residential code. What is unusual is the chimney-specific Director's Rule written on top of that code. Elsewhere the same questions go to the local building official, and the service-area page for each city above names the department that issues its permits.

Wherever the house is, ask that department the three questions you would ask SDCI: does this scope need a permit, what is the rebuilt chimney allowed to be built of, and what inspections are required along the way.