Why old brick chimneys fail first
An unreinforced chimney is brick and mortar stacked on itself, with no steel inside and nothing fastening it to the framing, so it moves on its own when the house moves and snaps where it is least supported, often at the roofline.
The Earthquake Country Alliance puts it plainly: during an earthquake these chimneys can collapse or break and fall on the roof, and tall slender chimneys are the most vulnerable. A two-story Portland foursquare with a narrow flue running well above the ridge is exactly that shape.
A chimney that is already leaning or pulling away from the house, or shedding mortar from its joints, has less to lose before it goes. When the decision is to take the stack down and build it back with reinforcing, that is a chimney rebuild; this guide is about the choice, and the rebuild page is about the work.
Many older Portland brick chimneys were laid without reinforcing or anchors, and many built before the 1930s have no clay liner either, which is a second problem in the same stack; our unlined brick chimney page covers the liner question.
What Cascadia means for Portland, in the agencies’ words
The State of Oregon’s hazard page puts about a 37 percent chance on a Cascadia megathrust quake at magnitude 7.1 or above in the next 50 years. The last Cascadia megathrust quake struck on January 26, 1700, at an estimated magnitude 9.0.
That is an offshore subduction quake, the kind that shakes the whole region at once. Smaller crustal quakes count too: Wikipedia’s account of the 1993 Scotts Mills quake, a magnitude 5.6 in Marion County south of the metro, says most of the structural damage consisted of toppled chimneys and failed unreinforced masonry walls.
What the chimney does during shaking
The house flexes and the chimney does not, so the masonry hinges at the roofline, the point where the stack stops being braced by the structure around it, and the section above either cracks loose or comes down.
Where it lands is the hazard. The Earthquake Country Alliance names both outcomes, bricks falling on the roof and bricks falling through it into the rooms below, which is why one of its listed fixes is plywood panels at the roof or above the ceiling joists to keep masonry out of the house.
Damage you cannot see from the yard matters as much. Shaking cracks clay flue tiles and opens mortar joints inside the flue, and a furnace or water heater venting into that chimney can push combustion gases into the house through the cracks. A chimney that looks fine from the sidewalk still earns a camera look after a quake.
Your options before the next one
There are six realistic options for an unreinforced house chimney, from strapping it to the framing to replacing it entirely, and FEMA’s own plan set warns that the retrofits improve performance but may not prevent damage or collapse.
FEMA P-1100-2C is a prescriptive plan set for one- and two-family wood-frame houses of three stories or less with solid brick chimneys of limited size, though it notes that houses listed as historic may need more. The table compares the options it and the Earthquake Country Alliance describe.
| Option | What it does | What it costs you in use | What the agencies say |
|---|---|---|---|
| Strap and brace the stack above the roof | Steel straps and angle braces tie the upper chimney to the roof framing | Nothing; the fireplace works as before | The Earthquake Country Alliance lists strengthening the chimney; no retrofit is promised to prevent damage or collapse |
| Plywood above the ceiling joists or on the roof deck | A deck that catches bricks instead of letting them fall into rooms | Nothing | An Earthquake Country Alliance option |
| Remove the chimney to the roof and cap it | Takes the heaviest, least supported masonry off the house | The fireplace can no longer be used, per the FEMA advisory | The most direct way to remove the hazard above the roof |
| Remove to the floor or ceiling below | Clears the masonry from the attic as well as the roof | Same; the flue is gone | A FEMA plan set option |
| Replace above the shoulder with a listed factory-built chimney in a braced chase | Keeps the firebox and lower masonry; a light metal flue runs up a strapped, angle-braced wood chase | The fireplace keeps working through the new flue | FEMA’s reuse options for a fireplace you want to keep |
| Rebuild with reinforcing and anchors | New masonry with steel inside and ties to the framing | The fireplace works and the look stays brick | Built to today’s code for new chimneys rather than a retrofit plan set |
The trade-off of removing the chimney above the roof
Taking the stack down to the roofline and capping it removes the part most likely to fall, and it also ends the fireplace, because an open fireplace with no flue above the roof cannot vent.
The FEMA advisory that the Building America Solution Center reproduces says exactly that: the chimney is shortened and capped at roof level to reduce its chances of detaching, and afterward the fireplace can no longer be used. For a fireplace that was already cold, or an orphaned furnace flue, that is no loss.
For a fireplace you want to keep, the middle path is FEMA’s shoulder replacement: masonry stays below the shoulder, and a listed factory-built chimney runs up through a framed chase that is strapped and braced. From the street it reads as a chimney; structurally it is a metal flue in a wood box.
A furnace or water heater still venting into the chimney needs its own path before the masonry comes down; see furnace and water heater flues for the choices there.
On permits, Portland’s page says chimneys may be repaired above the roofline without a building permit, while construction or repair of a masonry chimney otherwise takes a building permit priced on the project’s value. Seismic work that removes or replaces a stack is a question for the city before the first brick moves, and each suburb has its own desk.
What an inspection looks for in an old brick chimney
A Level 2 inspection answers the earthquake question for your specific chimney, from the roof and from inside the flue, and the list below is what we look at.
The result is not a seismic engineering report, which is a structural engineer’s job, but it tells you whether the chimney is sound enough to be worth bracing or already far enough gone that a rebuild is the honest answer; the repair or rebuild guide walks that decision.
- Plumb. We sight the stack from two sides. A chimney leaning away from the house, or with a gap opening at the siding, has already lost its bond with the structure.
- The roofline joint. Horizontal cracks in the mortar at the roofline are the hinge forming. Step cracks running diagonally through the brick say the same thing.
- Mortar condition. We probe joints with a pick. Mortar that powders out has little strength left; tuckpointing restores joints but adds no reinforcement.
- Height and slenderness. How far the stack rises above the roof and how narrow it is, since the tall slender chimneys are the ones the agencies single out.
- The crown and cap. A cracked crown has let water into the top courses for years, and wet, frozen brick breaks sooner.
- Inside the flue. The camera shows whether a clay liner exists, whether its tiles are cracked or offset, and whether anything is venting into the flue that would need a new path if the stack came down.
- The attic. Where the chimney passes through, we look for clearance to framing, old straps or braces, and any existing plywood deck.
Portland’s URM program is about buildings, not houses
Portland’s unreinforced masonry program, set out in city policy ENB-10.17, covers more than 1,600 known URM buildings and sets retrofit timelines for their owners; a single-family house chimney is not on that list, though it is the same material failing the same way.
We found no Oregon rule that requires an existing house chimney to be braced, so the decision is yours, made with the odds the state publishes and the shape of your own stack. Whether a fallen chimney would be covered is a question for your insurer, since earthquake coverage may be a separate policy, and it is worth asking before the shaking rather than after.
After an earthquake
After any quake you feel, stay out from under the chimney until someone has looked at it from the roof, and keep the fireplace and any appliance venting into it cold until a camera inspection has cleared the flue.
Look from the yard for new cracks at the roofline, bricks on the roof or ground, a cap or crown out of place, and a stack that no longer lines up with the wall below. Inside, mortar dust on the smoke shelf or hearth and a damper that no longer moves freely are signs the flue shifted.
CSIA’s written Level 2 procedure recommends a Level 2 inspection after a seismic event; the inspection levels guide explains why, and our chimney inspection page covers booking one. A carbon monoxide alarm on the floor with the furnace is the backstop while you wait.