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exposed chimney through ceiling detail

Megunticook | Posted in Construction Techniques on February 26, 2004 05:32am

Hi,

Trying to come up with a good detail for where an exposed brick chimney penetrates a sheetrock ceiling (2nd floor). The ‘rockers went right up against the brick and it doesn’t take much common sense to realize that’s not the safest situation!

I’m sure building codes specify a minimum clearance between the chimney and combustibles (I can look that up, but if anybody knows it offhand feel free to mention it). I plan to cut the ‘rock out from around the chimney to maintain that clearance.

The question is more of aesthetics–what detail do you use to hide the gap between brick and rock? An architect I know mentioned copper, which sounds nice but of course copper is an excellent heat conductor so that doesn’t seem like the greatest choice. Seems like you’d want something that’s not only non-combustible but non-conducting as well.

Any suggestions? Pictures would be most welcome! This seems like a good oppurtunity to get creative.

Thanks.

ps chimney is new, has 8″ flue tile inside and vents a wood stove on the 1st floor

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Replies

  1. YesMaam27577 | Feb 26, 2004 07:19pm | #1

    Seems like you'd want something that's not only non-combustible but non-conducting as well.

    I agree, and it sounds to me like drywall, and joint compound are perfect candidates. Niether is combustible,a nd neither is a good conductor of heat. The combination of the two is code-approved for fire-rated walls and ceilings (thickness of the DW makes a difference in the application/approval).

    If that doesn't sound like a good answer, then you could buy a few tubes of electrician's fire-stop caulk. It's pretty pricey, and you probably won't like the look without painting over it. But it is just as fire resistant as drywall.

    Vast projects should not be founded on half vast ideas.
  2. davidmeiland | Feb 27, 2004 05:45am | #2

    Monsieur, brick chimneys are often in direct contact with combustibles--check out any old farmhouse and see how the carpenters trimmed out right against the brick. I don't think the brick conducts enough heat to be a problem (someone smack me if I'm wrong), but in the distant future, when the mortar has cracked and the bricks have moved, heat will come through. I removed a brick chimney from my kitchen and there are several areas of scorched framing where joint cracks had developed and heat or even flame had come through. This was an old unlined chimney. You've got that liner, which is good.

    Now, as far as ceiling trim, I think I'd have some sort of heavy sheet metal 'casing' fabricated, with an edge sticking out to go into a groove in the chimney. I'd use a dry-cutting diamond wheel on an angle grinder to cut a 1/4" deep groove around the chimney for that edge to key into. Figure out how close to the ceiling you can cut. If you're lucky you might be able to make the groove in a mortar joint rather than into the brick. Have the tin man make the trim with miters that close as you put the pieces into the grooves. Tack it to the lid with some round headed brads and paint it the color of the ceiling. I can't really see something like this starting a fire. Heat would have to move from brick to metal to sheetrock to wood. You'd already be on fire if that happened.

    1. User avater
      Megunticook | Mar 02, 2004 12:39am | #3

      Good idea for the sheet metal detail.

      So fire code isn't really an issue here? I guess I always thought of sheetrock as "combustible."

      Interestingly, I've noticed a big crack in the sheetrock forming several inches from the chimney-- from excessive drying out I presume (must be a mud joint there?). If the stove's really cranking for a day or two the brick definitely gets pretty warm to the touch--which of course is the beauty of having it exposed upstairs.

      Is the clearance requirement from wood framing, on the other hand, a precaution in the event of a chimney fire?

      1. davidmeiland | Mar 02, 2004 12:58am | #4

        The paper face of sheetrock will burn and you don't want it directly against anything hot. I've had several occasions to rock around flue pipes and always keep the same clearance for rock as I would for wood (i.e. 1" clearance for B vent). There are always metal trim rings for those situations. I'm not suggesting that you should rock right against the brick, and I don't think you need to.

        I've always built on the west coast where there's little to no likelyhood of a new brick chimney. Taken several down and never seen a new one go up. So, I don't know the specifics on clearance from brick to wood. Your local building department will doubtless have something to say about it.

        1. xMikeSmith | Mar 02, 2004 03:58am | #5

          2" clearance from masonry chimney to framing..

          the rock can go right against the brick , but i'd leave a gap....

           your wood trim can go against the brick.. you have to use wide enough trim so you can nail into the framing that you held 2" back

          the gypsum is considered a non-combustible.. the paper can only char  , it will not support a flame spread   ... BY ITSELF... when it's painted.. the paint can support a flame spreadMike Smith   Rhode Island : Design / Build / Repair / Restore

          1. davidmeiland | Mar 02, 2004 05:26am | #6

            It doesn't make sense to put wood trim against brick if the required clearance for framing is 2"... either the brick is hot and wood shouldn't touch it, or it's not. What am I missing?

          2. Piffin | Mar 02, 2004 06:16am | #7

            The required clearance is 2" for FRAMING. It is zero for the immediate contact of wood trim as long as it is exposed if in an exterior application. Things get fuzzy for interior. The newest code allows zero when there is one full foot thickness of masonry between the heat source/channel and the wood in most situations.

            Now, here is some of the reasoning why it is OK to expose trim directly but not framing -

            When wood is repeatedly heated to a temp near it's flash point ( flash being that temperature when it will spontaneously burst into open flame, given a supply of oxygen) it will carmelize because the heat sort of charcoals the wood fibres and chemically changes some of it's properties. Wood that it repeatedly heated to some temp just short of flash point becomes a different monster, one with a lower flash point. It will then acheive spontaneous combustion much easier.

            In the vernacular, even if a chimney never gets hot enough to catch the wood on fire, if it gets hot often enough, eventually, it can catch the wood on fire.

            So, in a framing situation, a resident can live his life in the house and never see the framing to know whether it is charring or not. And if it does begin to smolder, it could do so for hours without his awareness.

            But ####trim molding such as a crown is fully exposed to the eye for daily inspection and it is presumed that one would notice a problem over the course of time.

            And, as with most things in life and construction, one thing must be weighed against another to determine the right way to deal with things. An open cavity surronding the chimney creates drafts and allows moisture to vent into the attic where you can develope condensation troubles, milds and other pernicious health hazards that are less dramatic but just as dangerous as fire.

            My own house has two sides of the chimney exposed upstairs. I plasterd the block directly and taped the corner to the sheetrock on the ceiling.

            The sheetrock is not a combustable. If it burns, the house is already engulfed.

            Mister Ed, the only concern i would have for you is that I know the area you live in here, being right across the bay from you, and I know how many of the older houses have no flue lining and how many have only a single bond course of brick. That would be a greater cause for concern than the sheetrock being in contact with it.

            Finally, a story -

            When we moved out here, the biog old house we rented had an exposed chimney running through one bedroom upstairs. I expect the exposure was the result of a DIY remodel there. The sheetrock was left cut back two inches in the same assumption you were making. It had then been stuffed with fibreglas ( a different kind of no-no)

            My daughter was about three YO back then and slept in that BRm. She often voiced concern for the "big mosquitoes" that visited her room every night. We wondered if she was having nightmares or was just overly bothered by a few of the pesky buggers.

            Finally one night a bat flew into the master bedroom and thje light came on - the one in my head. She lacked the vocabulary to describe a flying rodent but she was familiar with their comings and goings, her bed being right near the chimney.

            I trimmed it out immediately. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          3. User avater
            Megunticook | Mar 02, 2004 12:39pm | #8

            Thanks for the elucidation, Professor. I was actually wondering myself about the "flash point" thing--especially since the moisture content of any wood contacting the chimney would drop like a rock during a heating season.

            So NFPA standards allow for sheetrock and wood trim contact but no framing? Interesting. Next time I'm in the fire station I'll have to look at the language.

            By the way, this chimney is new and has an 8" flue tile liner inside. The masonry itself is 16" square. No cracked mortar joins with rusting old pie plates over unused stove thimbles!

            Great story about the "mosquitoes" and a good point, too. Reminds me of my wife's family's cabin over on the island (just a couple miles east of you)--they love the area where the chimney penetrates the roof and often at night you'll hear 'em flying around the cabin. By the way, when faced with a situation like that how do you make sure you don't trap the bats in somewhere when you do something like trim out the chimney? Could notice a rather unpleasant odor a few months later! Actually, when I cleaned out the chimney last fall I knocked down a dessicated bat which we'd never even noticed--but that was in the chimney.

            So just for the record, aesthetically speaking, what's your preferred method of trimming out a chimney around the ceiling (and floor, too)? Any photos?

            p.s.--you mentioned the fiberglass as a no-no. I noticed the insulation contractor (used the BIBS system) stuffed some fb batts around the chimney where it penetrates the roof in the attic. Every time I go up there I think "hmmmm. . .not sure I like that"

            Edited 3/2/2004 4:46:58 AM ET by MONSIEUR_ED

          4. Piffin | Mar 03, 2004 01:23am | #9

            This is a less objective answer because I don't know the code specifically, but I was a volunteer fireman for a few years. Twice, we pulled smoldering fibreglass out from direct contact with chimneys after chimney fires. In both cass, the brief chimney fire appeared to cause no damage to the flues, bricks or mortar, but the smoldering, melting, fibreglas set off the smoke alarms. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          5. davidmeiland | Mar 03, 2004 05:12am | #10

            On the one occasion I noticed, the insulation sub I used stuffed rock wool into the space between a chimney and framing. In a chimney fire, occupants often get on the roof and spray a bunch of water down the chimney. The sudden cooling can crack the mortar and/or brick and provide cracks thru which the fire spreads to the framing. When we go to chimney fires we take a big steel box with long handles and put everything from the fireplace into it and take it outside. If we're really happening we have the big fans set up and running before we do that so we don't smoke your house. If we're totally in control we have tarps and runners out before we do anything else.

            I don't doubt your response about the interior trim in contact with the brick, but I sure wouldn't trust my mother to notice it getting hot. The scorch marks around the two chimneys I took out of my house make me nervous about any wood anywhere near them. 2".... I guess.

          6. darrel | Mar 03, 2004 05:46am | #11

            This is a project way down the road...but I eventually plan to redo our upstairs and expose the brick chimney. Currently, the chimney is framed with 2x4s against the brick, and then sheetrocked. Is there any worry there? The chimney is an old brick one, probably one course thick, with fairly decent mortar from what I can see. It has a 8" flue liner that vents the HW heater and furnace.

            I had to punch a few holes in this wall (that's another story...) so I've looked at the framing, and it seems just fine. I can't imagine the chimney actually getting warm at all with the flue in it, but maybe this is something I need to be concerned about?

          7. davidmeiland | Mar 03, 2004 08:28am | #12

            Our house had a chimney in the kitchen. I've met folks who lived here 50 years ago and they had a large wood-burning cookstove in the kitchen that also heated water using a coil. I assume they burned a helluva lot of wood. The chimney was boxed in tightly with framing and 5/8" t&g. When I removed it I found scorch marks in a few places maybe 6 feet off the floor. This chimney was one brick thick and the mortar was sandy and cracked. Not a good situation. Yours sounds better... B-vent (?) inside the chimney for gas appliances, which lose less heat up the stack than most old woodburners, as far as I know. Maybe Piffin knows the code regarding a chimney with a metal liner in it, which may or may not be different than a straight fireplace.

            The house on this site before this one burned down around 1915. When I excavated to do foundation work I found tons of melted glass.

          8. Piffin | Mar 03, 2004 03:23pm | #13

            You have different requirements for B vent since you only have the burners on it. Solid fuels are harder to control and need the better chimney.

            Yes, I would be very concerned if you chimney has even the possibility of adding a solid fuel appliance to it, but as long as it is just these oil or gas burners, you are venting CO more than worrying about heat. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

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