Alberta Building Code
Smoke Chamber

9.22.7.  Smoke Chamber

​9.22.7.1.  Slope of Smoke Chamber

1)  The sides of the smoke chamber connecting a fireplace throat with a flue shall not be sloped at an angle greater than 45° to the               vertical.
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9.22.7.2.  Wall Thickness

​1)  The thickness of masonry walls surrounding the smoke chamber shall be not less than 190 mm at the sides, front and back, except  
      that the portions of the back exposed to the outside may be 140 mm thick.