I’m doing interior remodeling and have framed around the existing masonry chimney running up from the basement up through the main living floor, into the attic and out through the roof. I kept the studs the required distance away, and I need to install fire blocking between floors. Just what is the proper way to do this? Must it be metal or can i use durock? Once installed, can insulation be in contact with the masonry at any point up through the roof?
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Don't know about your local codes, but most masonry can have non-combustible insulation installed against it. Combustible insulations like cellulose can not be blown against chimneys- the trick is to wrap the chimney in appropriate areas with rockwool/fiberglass batts first and then blow the cellulose. You should be able to use either the Durock or metal as a stop.
You generally cannot put any insulation against aluminum/steel pre-fabricated chimneys.
Edited 1/6/2006 1:52 am ET by experienced
Thanks for the input. I wasn't sure about the durock. Is there something in particular that I should use to seal the seam between the metal flashing or durock? The chimney is only there to vent the flu gases from the oil furnace, so I'm not really concerned about the temp of the masonry blocks igniting anything, but I do want to stay in code. The ceiling of the furnace room will be finished off with 5/8" drywall. I'm going to insulate between the wall studs surrounding the chase with R11 fiberglass, or rockwool batts if I can find them around here, before I drywall. I would like to beef it up beyond R11 if possible. I assume from what you say that I can place insulation in the gap between the floor joists and the chimney at each floor, i.e. under the firestops? Right? What I want to do most of all is to keep the usable heat around the chimney from all those precious spent petrodollars in the house rather than heating the sky.
Check with local codes on the "insulation against masonry" item as previous post says it is not legal in US (???).
To seal the metal/Durock to the flue where it penetrates the thermal envelope of the house, use a high temp silicone (usually reddish colour).
Is the flue up through the heated part of the house? If so, do not insulate the stud cavities around it as you'll stop heat loss into the rooms around the chimney. Just do a hell of a job airsealing/insulating at the thermal layer.
Makes sense. Nice to be able to have input.
My favorite way to dal withthis is to use a metal angle 1 ga. But I ppl;ace it and fasten in under each bottom plate as I work up. Plain stock may work too, but I feel that the angle will help prevent it from warping under heat streeess.
No fibreglas can be used against a masonry chimney here. Must be different inb canada where experienced lives. I have personally seen the results of two fires with FG glowing hot in a fire around a chimney,. one was the source oif the call to the fire dept.
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