Unreinforced brick masonry chimney stacks

An overview of the hazards caused by unreinforced brick masonry chimney stacks and potential strengthening solutions.

To find solutions that are appropriate for your building, consult a structural engineer for a professional assessment.

Unreinforced brick masonry chimney stacks image
Image courtesy of Win Clark


Pieces of chimney stack break off or the entire chimney stack collapses.

Potential structural strengthening projects

a. Fit a galvanised steel tube into the chimney flue and grout it in place.

b. Mortar stainless steel Helifix bars around the perimeter of the chimney-stack to form a series of hoops. Mortar them into selected horizontal joints of the brickwork.

c. Make a structural frame from steel angle sections and install them within a ceiling space, fitting them snugly around the four sides of the stack. Fix the four sides of the frame together by bolting them at the corner junctions. You can use proprietary steel strap bracing, fitting it to the ceiling or roof framing where the loading from the chimney stack is to be transferred to bracing walls.

d. Where a chimney stack may fall away from the building, you can tie it back into the building at the level of the floor or roof structure (diaphragm). Form the tie at each level from a galvanized flat steel bar that is formed into a two-piece frame (yoke). Fit each piece and fix it around the chimney-stack, through the wall and twist it flat to fix it to the floor framing under the plywood structure (diaphragm).

Possible first steps with a structural engineer

They assess the structural capacity of the chimney stack and provide specifications for required strengthening work.