Our house is a single story house in Southern California with an unconditioned attic. I am working to improve the air sealing in the attic. Most of the attic is conventional joists over a drywall ceiling. But around the chimney, there are huge cavities going down to the firebox and far down into the stud wall in the living room.
What should I do to close these cavities off? I am thinking of constructing a metal platform with rebar, metal plates and maybe an inch of mortar. Then, it needs a partition to allow insulation to be installed, but kept away from the chimney. Then, I can apply fire safe sealant around 8″ of the chimney.
There is also framing within an inch or two of the chimney. I expect I need to rework that also.
Thanks in advance for your responses.
Replies
Is this a metal chimney or masonry?
In either case you can modify as needed to get the framing 2 inches away, (being careful to make sure your framing properly supports what it needs to)
and then use sheet metal to bridge the gap between the wood framing and the chimney, then you can use high temp sealant around the chimney.
If you make the sheet metal angle up after the framing, it should provide a suitable barrier to keep your insulation away from the chimney.
Thanks, Uncle Mike
The chimney is masonry. The house was built in 1981. There is an attic floor joist that runs right along the masonry chimney. I have a chance of altering that ( with a lot of work and stress for me! ). A joist on the other side has a 2" clearance, so that is good. Both rest on a large cross beam that must be 8" x 6" and it rides against the masonry. I would have to take apart most or all of the living-room wall, which is masonry with an adhered rock face, in order to fix that. I see it as prohibitive.
I appreciate your input in air sealing up to the masonry. I have pictures, but they are JPEGS that exceed the 3 meg limit of the forum.
You can find an application online that reduces photo size.
One thing that might help is to have the chimney lined. They install a stainless steel liner and surround with an insulating layer.
Ii am not an expert on this, but it seems like doing so would reduce the danger of combustion gasses contacting the framing.
https://www.finehomebuilding.com/forum/framing-for-chimney-3
Discussion indicates a rated liner can replace the clearance requirement.
You may find it cheaper to have the chimney lined than to rebuild framing that close.
We had our chimney relined, and the firm indicated that 50 years is about it for a clay lined chimney, so you might be getting ready for this in any case before too long.