Thursday, June 18, 2009

Chimney Support Installation

I'm putting a wood stove in the house and I want to have the chimney installed through the roof before I do the shingling.

The chimney is supported by a metal box that hangs below the bottom of the roof trusses and protrudes out through the top of the roof sheathing. The actual chimney itself sits inside the metal box.

The Building Code specifies that there be a space between the chimney and any combustible material. When using a metal support box like this, a 1" space is required. Without a metal support box, a 2" space is required.

To determine exactly where the chimney had to go, I first had to figure out where the wood stove will sit. That too is goverened by clearances that must be maintained between the stove and any combustible material.

Once I had the exact stove location determined, I marked the spot on the floor where the centre of the chimney outlet on the stove will be. Then I hung a string-line from the roof trusses, and moved it around until it hung directly over top the mark on the floor. That gave me the location of the center of the chimney, and I determined where to put the chimney support box based on that.

The bottom of the support box is attached to the roof trusses by metal brackets which adjust to the space between the roof trusses. At the top, I framed around the support box, and then used another type of metal bracket to attach the support box to the framing.

Once the roof sheathing is complete, I'll cut off the top of the support box flush with the roof. The chimney flashing will then cover everything up.