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  1. #1
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    Question Am I overthinking this??

    Nice brick Chimney structure seen from the outside. When I get into the attic it is a masonry chimney about 5 ft tall on stilts.
    While this has stood the test of time since 1993, should ther be more "beef" to the support structure, like solid sides for more stability? I did notice the little bow in one of the 2x4's on front right.
    Or am I overthinking this?

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  2. #2
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    Default Re: Am I overthinking this??

    It cannot have insulation in contact with the chimney--typically a 2" clearance, which is an air space. Insulation will keep that area warmer than designed resulting in pyrolysis and perhaps many years later, fire. We cannot see but there must be a listed firestop in the attic, supposedly on top of the joists. There must be an attic insulation shield to prevent this from happening. If vertical fireblocking is required in this jurisdiction then the whole chase would need to be sheathed from the attic floor to the underside of the roof deck, which is also desirable in containing an unfriendly fire.

    As for the structural support of the masonry, that's a call for the AHJ but typically, that load would have to be engineered or spread over several joists bilaterally until the strongbacks rest over a load bearing wall or column. There is little inherent stability in this brick starting so close to the roof deck as this junction would form a hinge point. It is surprising it hasn't at least opened up the flashing causing water intrusion. Also, as that framing dried out, it would have shrunk thus dropping a little at the flashing. They must have a decent overlap or sliding joint. There are no diagonal braces for shear strength. At the very least, sheathing it would help this. I'd sheath it with Thermo-Ply and be done with it once the insulation has been cleared out and the listed firestop confirmed properly installed and proper fireblocking. I call these out all the time for full sheathing because all it takes is one good storm to whip up that blown insulation and have it 'snow' all over the firestop again. BTW, where I've seen these faux masonry chimneys made of real masonry units they typically bed them on angle irons such as lintels that are secured to the framing. No way would this pass in a seismic zone.

    Note that in attics where contact with the chase could be reasonably anticipated, the chase would have to be enclosed to protect the chimney from incidental contact.

    Keep the fire in the fireplace.

  3. #3
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    Default Re: Am I overthinking this??

    Not overthinking a bent 2X4. That sounds like it should all be removed and that is what I'd recommend probably, maybe as a future upgrade if it is stable now.

    John Kogel, RHI, BC HI Lic #47455
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  4. #4
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    Default Re: Am I overthinking this??

    It is poor construction. At the very least installing sheathing on the framing will prevent possible lateral movement or buckling. It has performed o.k. because the load is not that high.


  5. #5
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    Default Re: Am I overthinking this??

    From the IRC:
    - R703.7.2 Exterior veneer support. - - Except in Seismic Design Categories D0, D1 and D2, exterior masonry veneers having an installed weight of 40 pounds per square foot (195 kg/m2) or less shall be permitted to be supported on wood or cold-formed steel construction. When masonry veneer supported by wood or cold-formed steel construction adjoins masonry veneer supported by the foundation, there shall be a movement joint between the veneer supported by the wood or cold-formed steel construction and the veneer supported by the foundation. The wood or cold-formed steel construction supporting the masonry veneer shall be designed to limit the deflection to 1/600 of the span for the supporting members. The design of the wood or cold-formed steel construction shall consider the weight of the veneer and any other loads.

    Typical 4" brick veneer weight is 40 pounds per square foot (meeting the exception above).

    However, masonry veneer has anchoring requirements to the structure behind it (and there is no structure behind that brick) ... does that brick chimney meet the requirements for a brick wall as it is not a masonry veneer ... or is it considered as brick veneer anyway? Typically, veneer will either be anchored (with ties) or adhered (adhered directly to the supporting structure behind the veneer).

    Any of our engineers out there?

    Jerry Peck, Construction / Litigation Consultant
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  6. #6
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    Default Re: Am I overthinking this??

    I'm not seeing any over-thinking Jeff. I'd be putting the monkey on someone else's back if I was writing the report.

    Eric Barker, ACI
    Lake Barrington, IL

  7. #7
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    Cool Re: Am I overthinking this??

    Thanks for the input. I agree the minimum would be enclosing the chase for additional strength and vertical fireblocking. The flashings were good but the shingles were just replaced 3 years ago so the history left with the older flashings.
    I too have seen steel angle or lintels used to support these in the past.
    I appreciate your help and guidance as always.


  8. #8
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Jerry Peck View Post
    From the IRC:
    - R703.7.2 Exterior veneer support. - - Except in Seismic Design Categories D0, D1 and D2, exterior masonry veneers having an installed weight of 40 pounds per square foot (195 kg/m2) or less shall be permitted to be supported on wood or cold-formed steel construction. When masonry veneer supported by wood or cold-formed steel construction adjoins masonry veneer supported by the foundation, there shall be a movement joint between the veneer supported by the wood or cold-formed steel construction and the veneer supported by the foundation. The wood or cold-formed steel construction supporting the masonry veneer shall be designed to limit the deflection to 1/600 of the span for the supporting members. The design of the wood or cold-formed steel construction shall consider the weight of the veneer and any other loads.

    Typical 4" brick veneer weight is 40 pounds per square foot (meeting the exception above).

    However, masonry veneer has anchoring requirements to the structure behind it (and there is no structure behind that brick) ... does that brick chimney meet the requirements for a brick wall as it is not a masonry veneer ... or is it considered as brick veneer anyway? Typically, veneer will either be anchored (with ties) or adhered (adhered directly to the supporting structure behind the veneer).

    Any of our engineers out there?
    Because it is a box-like structure it is much more stable than a typical brick veneer. Since the chimney is relatively short I'm sure wind loads would not be high enough to cause the chimney to tip or slide. It


  9. #9
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    Default Re: Am I overthinking this??

    Counting bricks, assuming 5 lb per brick, that masonry weighs well over a ton. Just looking at the structure in photos, I do not like it. The studs don't seem to be tied together in the middle, hence the bowing. I therefore question how they are supported from below.
    Basically, I think "If one was trying to design a wooden support structure to hold up 1.25 tons, how would they go about it?" Many variations are possible, but I don't think many of them look like that.


  10. #10
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    Default Re: Am I overthinking this??

    Quote Originally Posted by gary carroll View Post
    Counting bricks, ...
    Counting bricks ... what size is it? I.e., How many square feet?

    Multiply the size in square feet by 40 pounds per square foot and you will get the approximate weight presumed by the code.

    Jerry Peck, Construction / Litigation Consultant
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  11. #11
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Jerry Peck View Post
    Counting bricks ... what size is it? I.e., How many square feet?

    Multiply the size in square feet by 40 pounds per square foot and you will get the approximate weight presumed by the code.
    I did it this way:
    27 bricks high on the high side, x 4 wide = 108 bricks
    15 high by 4 wide on the short side = 60 bricks
    Each long sides is (27+15)/2 = average 21 high by 6 wide, two of them, so 21 x 6 x 2 = 252 bricks.

    252 + 60 + 108 = 420 bricks.
    Weight of average 8 x 4 x 2.25 brick is 5 pounds, so 5 x 420 is 2100 lbs.
    This does not take into consideration mortar, cap, flashing, etc.
    I figured that is at least another 150 pounds in mortar and cap, so 2250 pounds, so 2 1/4 tons.
    This is on the light side since the mortar probably really weighs more than that.

    The approximate weight by code presumption calculation would be 420 bricks times 20 sq inches per brick (or a little more depending on the mortar gap) = 420 * 20 = 8400 sq/in, divide by 144 to get sq ft is 8400/144= 58.33 sq feet, times 40 = 2300 lbs.

    So, within 50 pounds either way, not significant.


  12. #12
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    Default Re: Am I overthinking this??

    How many pounds in a square foot of materials.
    Hope that helps.
    http://tinyhousecommunity.com/docs/w...-materials.pdf

    ICC http://www2.iccsafe.org/states/Flori...20Material.pdf

    Roughly 4 to 5 pound per brick dressed, standard or metric.
    7 bricks in a square foot.

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  13. #13
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    Default Re: Am I overthinking this??

    Wow, that's bad!! See IBC Section 2113 for masonry chimneys, which requires vertical and horizontal reinforcement and support on a concrete or masonry foundation. If that's not enough, IBC Section 2304.12 requires an engineer to check wood framing supporting masonry construction. I wouldn't call it veneer since veneer, as Jerry mentioned, must be anchored to a wall per IBC Section 1405. No, Jeff, you are NOT overthinking this, and are right to be concerned.

    Last edited by Thom Huggett; 05-10-2016 at 05:04 PM.
    Thom Huggett, PE, SE, CBO

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    Default Re: Am I overthinking this??

    Quote Originally Posted by Thom Huggett View Post
    Wow, that's bad!! See IBC Section 2113 for masonry chimneys, which requires vertical and horizontal reinforcement and support on a concrete or masonry foundation. If that's not enough, IBC Section 2304.12 requires an engineer to check wood framing supporting masonry construction. I wouldn't call it veneer since veneer, as Jerry mentioned, must be anchored to a wall per IBC Section 1405. No, Jeff, you are NOT overthinking this, and are right to be concerned.
    I'm not saying its good, but IBC does not generally apply to most residential structures. I'd have to look into what they are referring to as vertical and horizontal reinforcement. I have never seen residential chimneys reinforced. I do work in a low seismic area though.


  15. #15
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    Default Re: Am I overthinking this??

    So how is the weight of the masonry section carried down to proper bearing below to basement.? The wood framing appears to be solely resting on the ceiling joists?


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    Default Re: Am I overthinking this??

    Quote Originally Posted by Raymond Wand View Post
    So how is the weight of the masonry section carried down to proper bearing below to basement.? The wood framing appears to be solely resting on the ceiling joists?
    Raymond, concentrated loads such as the chimney, or grand piano for that matter, require an engineer to evaluate the structure.
    Concentrated loads cause defection, rotation, cupping, crushing, shear damaged, etc.

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  17. #17
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    Default Re: Am I overthinking this??

    I know that. I am asking how that load is carried down past the joists.


  18. #18
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Raymond Wand View Post
    I know that. I am asking how that load is carried down past the joists.
    I can only suspect, as with others and the OP, bearing walls and beams.
    I suspect those are supported by columns. Unless it is a gravityless space.

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  19. #19
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Raymond Wand View Post
    So how is the weight of the masonry section carried down to proper bearing below to basement.? The wood framing appears to be solely resting on the ceiling joists?
    Hard to tell. The rear side in the photo look like it is probably resting on a bearing wall because it looks like the ceiling joists are spliced there. At the sides it looks like maybe a top plate or some framing adjacent to the ceiling joists. Since the chimney would be enclosed in the house maybe there is wall framing below all sides down to ?

    I don't like it, but if it has not moved in over 20 years I would probably put sheathing on the framing in the attic, frame around the bottom of the brick to limit lateral movement, and call it a day. Now if someone else was willing to pay the money to do it right, my answer may be different. Just trying to be realistic about making improper construction better than it is.


  20. #20
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Mark Reinmiller View Post
    I'm not saying its good, but IBC does not generally apply to most residential structures. I'd have to look into what they are referring to as vertical and horizontal reinforcement. I have never seen residential chimneys reinforced. I do work in a low seismic area though.
    OK, so see Chapter 10 of the IRC for the identical information on the chimney. R1001.2 and R1003.2 both require a masonry or concrete foundation. They even have a pretty picture on how to construct it (figure R1001.1) The southern portion of Indiana (you are in Indiana, right?) is in seismic zones Do and C which would require reinforcement (see IRC Table R301.2(2)). Also, see IRC Section R606.12.2.2 for reinforcement requirements. At a minimum the wood studs should have sheathing applied to brace them. This is a situation that will come crashing down on someone's head someday.

    Thom Huggett, PE, SE, CBO

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    Default Re: Am I overthinking this??

    Quote Originally Posted by Thom Huggett View Post
    OK, so see Chapter 10 of the IRC for the identical information on the chimney. R1001.2 and R1003.2 both require a masonry or concrete foundation. They even have a pretty picture on how to construct it (figure R1001.1) The southern portion of Indiana (you are in Indiana, right?) is in seismic zones Do and C which would require reinforcement (see IRC Table R301.2(2)). Also, see IRC Section R606.12.2.2 for reinforcement requirements. At a minimum the wood studs should have sheathing applied to brace them. This is a situation that will come crashing down on someone's head someday.

    I am in PA. I agree that it is wrong. With sheathing and some lateral support it should remain sound for a very long time (assuming it is well supported vertically below what we can see). But the reality is that it has been there for 20+ years, the load is much less than a typical chimney, and nobody is going to tear the house apart to construct a proper support system.


  22. #22
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Thom Huggett View Post
    OK, so see Chapter 10 of the IRC for the identical information on the chimney. R1001.2 and R1003.2 both require a masonry or concrete foundation. They even have a pretty picture on how to construct it (figure R1001.1)
    That pretty picture is of a masonry chimney, the photo in the original post is only showing a chimney enclosure (the "chimney" is inside it - it is metal pipe, likely triple wall, and the 'masonry chimney' as has been discussed is nothing other than a framed and stuccoed 'frame chimney' in that both are really not "chimneys", they are 'chimney enclosures', and the 'chimney enclosure' under discussion happens to be masonry).

    No masonry or concrete foundation is required for the 'chimney enclosure' under discussion, however, the masonry does need to meet the maximum 40 pounds per square foot load and the framing needs to be designed to support that load - as is required by the code.

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  23. #23
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    Default Re: Am I overthinking this??

    You guys in non-seismic areas think a lot different than we do in seismic areas. I have personally seen a brick chimney laying in pieces all over someone's back yard after a rather minor earthquake because the contractor didn't grout between the flu and the brick. It was an empty brick tube, just like in Jeff's photos, and thank God no one was standing next to it at the time.

    This is one of 3 different things. It is either a chimney (I don't know what a "chimney enclosure" is nor where it is covered in the IRC), or brick wall, or veneer.

    Veneer, by definition, is adhered or anchored to a wall. This does not appear to be the case, so IRC 703.7 does not apply.

    If it is a brick wall it must be constructed according to IRC Section R606. Section R606.4 requires masonry support to the foundation and R606.12.2.2 requires horizontal and vertical reinforcement.

    If it is a chimney it must comply with IRC Chapter 10, which also requires reinforcement and a foundation as I already stated.

    It seems pretty clear to me.....

    Thom Huggett, PE, SE, CBO

  24. #24
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Thom Huggett View Post
    You guys in non-seismic areas think a lot different than we do in seismic areas. I have personally seen a brick chimney laying in pieces all over someone's back yard after a rather minor earthquake because the contractor didn't grout between the flu and the brick. It was an empty brick tube, just like in Jeff's photos, and thank God no one was standing next to it at the time.
    Correct.

    It is an empty brick tube. I have also seen them lying on the ground and on roofs from high wind events ... no shakey earth here.

    it is a chimney it must comply with IRC Chapter 10, which also requires reinforcement and a foundation as I already stated.

    It seems pretty clear to me.....
    Yep ... pretty clear that it is an empty brick tube as it does not resemble those pretty pictures of masonry chimneys the IRC shows.

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  25. #25
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    Default Re: Am I overthinking this??

    It is a brick "chase".

    Keep the fire in the fireplace.

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    Default Re: Am I overthinking this??

    Quote Originally Posted by Bob Harper View Post
    It is a brick "chase".
    What are the elements that make up a "chase"? The IBC defines a wall as, "A vertical element....used to enclose space." (I know some of you don't like the IBC, but it is published by the same organization as the IRC, and the IRC definition is worthless). So if you want to insist that this is not a chimney, then call it a "chase," and the chase "walls" must meet IRC R606.

    Now, what to do about it. As has been previously stated, tearing down the house to install a foundation is not practical. I suggest that the situation be reviewed by a licensed engineer, who would probably require additional framing and sheathing on the support structure in the attic, and also perhaps some external bracing of the brick structure to the roof. It should at least be cited in any report as a possible falling hazard in the event of high winds or seismic activity.

    Thom Huggett, PE, SE, CBO

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    Default Re: Am I overthinking this??

    One could mechanically attach ties to the brick from inside, construct walls up inside, then attach the ties to the wall, making it unto defacto brick veneer.

    It would still require an engineer to sign off on it ... but that puts us all the way back to my earlier post about it and why it is not brick veneer ...

    At least the brick would be anchored in place so Thom, I, and others won't find the brick laying on the ground or the roof.

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  28. #28
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Thom Huggett View Post
    If it is a chimney it must comply with IRC Chapter 10, which also requires reinforcement and a foundation as I already stated.
    It is not a chimney by definition:

    2012 IRC (underlining is mine)
    - CHIMNEY. A primary vertical structure containing one or more flues, for the purpose of carrying gaseous products of combustion and air from a fuel-burning appliance to the outside atmosphere.
    - CHIMNEY TYPES.
    - - Residential-type appliance. An approved chimney for removing the products of combustion from fuel-burning, residential-type appliances producing combustion gases not in excess of 1,000F (538C) under normal operating conditions, but capable of producing combustion gases of 1,400F (760C) during intermittent forces firing for periods up to 1 hour. All temperatures shall be measured at the appliance flue outlet. Residential-type appliance chimneys include masonry and factory-built types.

    The definition of a chimney defines the factory-built chimney pipe inside the enclosure.

    Thom, what do you call a frame structure with stucco on it which encloses a factory-built chimney, i.e., what is shown except that it would be frame walls and stucco - you would call that what?

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  29. #29
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    Default Re: Am I overthinking this??

    Quote Originally Posted by Jerry Peck View Post
    It is not a chimney by definition:

    2012 IRC (underlining is mine)
    - CHIMNEY. A primary vertical structure containing one or more flues, for the purpose of carrying gaseous products of combustion and air from a fuel-burning appliance to the outside atmosphere.
    - CHIMNEY TYPES.
    - - Residential-type appliance. An approved chimney for removing the products of combustion from fuel-burning, residential-type appliances producing combustion gases not in excess of 1,000F (538C) under normal operating conditions, but capable of producing combustion gases of 1,400F (760C) during intermittent forces firing for periods up to 1 hour. All temperatures shall be measured at the appliance flue outlet. Residential-type appliance chimneys include masonry and factory-built types.

    The definition of a chimney defines the factory-built chimney pipe inside the enclosure.

    Thom, what do you call a frame structure with stucco on it which encloses a factory-built chimney, i.e., what is shown except that it would be frame walls and stucco - you would call that what?
    I am willing to call it a "chase." So, a chase has walls, and the wall construction, whether wood, masonry, steel or concrete, needs to comply with the appropriate section of IRC Chapter 6. Regardless of the semantics, in my opinion this is a hazardous situation which the home owners need to be advised of.

    Thom Huggett, PE, SE, CBO

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    Default Re: Am I overthinking this??

    It is not a chimney as previously noted. The "chimney" in this case is the metal listed chimney within the chase. For construction under the IRC not to exceed three stories you can use a 'chase'. Once you exceed three stories, the construction falls under the IBC, which calls for fire rated construction making this a "shaft" and must meet the code for fire rating based upon the occupancy and type of construction. This would include firestops listed to ASTM E-814/ UL 1479, which is a hose stream test. Your typical listed firestop for a factory built chimney cannot pass this test nor are any I'm aware of tested to it. Therefore, technically, factory chimneys should never exceed three stories.

    Such a brick chase supported by frame construction would require the AHJ to sign off since it is not directly addressed in the code. You'd need to calculate the dead load and live load including wind load for that exposed cross-sectional area for your Zone then figure out how you're going to transfer that load to a column or engineered beam. Simply slapping some lintels on a few two-bys spiked into whatever nearby framing you feel like doesn't cut it. For one, there is a lot of flexion in such a chase. Between the lumber shrinking as the house dries out, the wind and storms, and the settling from the dead weight all can cause flashing to open up or the wythe wall to crack and fail. The fact it has held up this long is nice but that doesn't make it right.

    This type of construction is done all the time. As long as the cross-sectional area and wind loading aren't too severe and they extend all the way to the ceiling joists for inherent stability they seem to survive well enough. Those perched up on a shelf with only a few feet of the masonry wythes extended down into the attic are not very stable laterally. If the minor side is very narrow making it a high aspect/ ratio chase, it can be extremely unstable. I've investigated and replaced many blown off at the roofline by storms.

    The free flow of air circulating up into the chase is drying the moisture driven in by vapor diffusion. If you seal off the base of this at the lintel with firestopping or fire blocking it will become a soggy sponge and the lintels will rust quickly.Still, you'd need to check with your AHJ regarding vertical fireblocking, attic insulation shielding and a listed firestop on top of the ceiling joists. Since this is pushing the 10ft rule, he may want another firestop/block.

    As for chimney height above the roofline, you measure from the flue gas outlet on the uphill side of the listed chimney pipe and not the masonry wythe: 3/2/10 rule.

    Keep the fire in the fireplace.

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