Q: Our home has an older metal-framed woodburning fireplace built into an inside wall. An area of the adjoining room was boxed in to provide...
Q: Our home has an older metal-framed woodburning fireplace built into an inside wall. An area of the adjoining room was boxed in to provide adequate airspace behind the fireplace. The boxed-in area is approximately 3 ½ feet deep by 4 feet across and extends to the attic above.
The fiberglass insulation in the attic partially covers the opening but is 2 inches back from the chimney, as is required of all combustible materials. This gap around the chimney leaves the uninsulated walls surrounding the fireplace partially exposed to the cold attic air. I am able to climb down into the area from the attic.
Would you recommend insulating the walls, or are there other considerations or safety concerns?
A: Combustible materials must be 2 inches from the triple wall stove pipe, as you correctly pointed out, but a chimney chase must be completely sealed with a metal collar. You should not be able to climb from the attic to your fireplace.
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Besides being a heat/comfort issue, this a safety hazard. You are missing what is commonly known as fire blocking. A fire block prevents flames from spreading to the attic and engulfing the house.
A fireplace shop can help you find a manufactured metal collar for the diameter of the flue pipe that may also span across the opening of the 3 ½-foot by 4-foot chase. The metal goes tightly around the pipe at the floor level of the attic and is then covered with (preferably) rock wool insulation to within 2 inches of the flue pipe (there are now great heat-resistant caulking products that will eliminate even the smallest gap in the metal).
Do not insulate the side walls. It’s not needed with the insulation over the top of the fire block. It could also be a hazard if it fell.
If the fireplace shop doesn’t have the right collar, a person reasonably handy with tin snips could cut one out of a larger-gauge piece of sheet metal.
Darrell Hay is a local home inspector and manages several rental properties. Send home maintenance questions to firstname.lastname@example.org. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.