Thread: Attic: Fireblock around chimney?

We are in the process of selling our home and an inspector has said we need a firebarrier for our chimney in the attic of our home.

We are in Georgia, our house was built in ~2006.

The fireplace is on the first floor, the chase is covered in drywall on the 1st and 2nd floor. There is a barrier within the chase between the first and 2nd floor, and there is a block between the 2nd floor and the attic.

1) is what I have made to code (grandfathered?)
2) if I need to do something, what do I need to do? I have been told anywhere from 1/8" drywall to 5/16" drywall to cement board to...

*Note in the pictures ignore the plywood "flooring", I pulled that up there so I had a surface to work on...

Thanks for your help!
Ryan

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Looks like someone had the right idea ... just did not understand the idea and thus their execution of their understanding of the idea went astray.

In the photo looking down into the framed out chimney area, you see that OSB 'floor' with the firestop in it through which the chimney goes?

That OSB should be up at the level where the higher ceiling is, right up at the attic floor.

I would leave that OSB and firestop support down where it is ... just install another piece of OSB and another firestop support at the attic floor (will save a lot of work, and will also save potentially damaging something trying to get that OSB and firestop support out from where it is).

Also, the insulation should not be within 1" of the chimney (likely has a minimum 1" clearance label on it).

I hope there is a cricket at that chimney on the roof - it looks to be 6' to 8' wide.

I dont think the inspector will let me do that. His comments were pertaining to wrapping the chase. I was thinking of wrapping the 3 sides of the chase in the attic with 1/2" drywall and taping/mudding the seams/screws ???


Thats the problem...he commented that the chase wasnt wrapped but didnt reference any codes it was in violation of and he hasnt called me back to provide clarification.

Originally Posted by Ryan Guilette

His comments were pertaining to wrapping the chase.
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Thats the problem...he commented that the chase wasnt wrapped but didnt reference any codes it was in violation of and he hasnt called me back to provide clarification.

Tell the inspector you need clarification regarding what he is wanting and the code backup for what he is wanting. Tell him you need to know so you can put that information down on the permit to do the work.

If the inspector cannot support what he is telling you that you need to do ... tell the inspector to issue a revised and updated report showing what he can backup with documentation or showing the issue has been addressed and no longer exists (the condition may still exist, but without backup to support what he wants the issue has been addressed and no longer exists).

The fireplace must be installed in accordance with the mfrs. listed instructions and the building code. All the mfrs. I'm aware of defer on chase construction to the local building code. In this regard, most are similar in that they call for "fireblocking" between floors or every 10 feet vertically and a listed firestop installed per the mfr. at each ceiling and attic floor level. This appears to have a listed firestop at the wrong level. Also, the OSB must be 23/32" and all the stud bays effectively blocked. Those loose unfaced batts of insulation are a problem and must be sheathed over to prevent them from falling against the hot chimney and to enclose the insulated cavity so it provides the stated 'R' value. There is nothing in any of the major model codes for residential applications that requires any type of fire resistive drywall to line the chase. Unless there is a local ordinance to that effect then you can use the same materials approved for use in the rest of the living space: drywall, paneling, etc. However, the best product I have found is thin structural panels such as Thermo-Ply or Thermo-Sheath. This material is about the same thickness as cardboard but very stiff with a fiberglass scrim reinforcement. It has a low flame spread and is not good food for mold the way drywall is. You can bend corners with it an nail it up with roofing nails. I use one piece to wrap around the three walls then use UL 181 foil tape over the seams to block cold air infiltration.


If you do have another fireblock with listed firestop installed at the attic floor level, you'll need either an attic insulation shield around that chimney pipe or better yet, seal off that opening with T-ply so the chimney is no longer visible. This prevents insulation from coming in contact with the hot chimney but it also helps to encapsulate the chase in the event of an unfriendly fire. This simple step can mean the difference between people having time to exit the burning building or not.

FYI, most factory chimney carries a 2" clearance to combustibles but there are some 1.5" and a few 1" so read those listing labels on the pipe or in the IOM book for that model fireplace.

hth

Originally Posted by Jerry Peck

Looks like someone had the right idea ... just did not understand the idea and thus their execution of their understanding of the idea went astray.

In the photo looking down into the framed out chimney area, you see that OSB 'floor' with the firestop in it through which the chimney goes?

That OSB should be up at the level where the higher ceiling is, right up at the attic floor.

I would leave that OSB and firestop support down where it is ... just install another piece of OSB and another firestop support at the attic floor (will save a lot of work, and will also save potentially damaging something trying to get that OSB and firestop support out from where it is).

Also, the insulation should not be within 1" of the chimney (likely has a minimum 1" clearance label on it).

I hope there is a cricket at that chimney on the roof - it looks to be 6' to 8' wide.

If that chimney is going through the lower perimeter ceiling, of say a bedroom tray ceiling, would that not be the correct place for the firestop? That drywall ceiling is the attic floor at that location; all attics are not level!

Looking again, hard to say what type ceiling it is. Can't see why they went to so much trouble to put it at a lower level though.

Originally Posted by Vern Heiler

If that chimney is going through the lower perimeter ceiling, of say a bedroom tray ceiling, would that not be the correct place for the firestop? That drywall ceiling is the attic floor at that location; all attics are not level!

You would be correct if that was an attic which had different ceiling heights over different areas, however, that appears to have walls on all four sides, which means it is just dropped down like a soffit.

That looks to be on an outside wall.

That makes that done incorrectly and the firestopping should be level with the ceiling.

The photos are a bit confusing. I don't think it would be a hazard if the chase was fully blocked at the elevation of the OSB (without gaps between the OSB and blocking). However, I suspect it is not. For the experts out there, if the stud cavities were blocked with 2x6s that extended out over the OSB at all sides and then fire-caulked, would that provide a proper barrier?

Originally Posted by Mark Reinmiller

... if the stud cavities were blocked with 2x6s that extended out over the OSB at all sides and then fire-caulked, would that provide a proper barrier?

Not based on what I am seeing the photo showing.

The fireblocking should be at the ceiling level, the attic floor level - based on what I see in the photo.

Start at the attic: regardless of how many ceilings there are below, there MUST be a firestop surrounded by fireblocking with an attic insulation shield at the attic level. Now, EACH ceiling below must have a listed firestop with code approved method of fireblocking. Now, at the ceilings, the firestop goes on the under side. At the attic, the firestop goes on top. Whatever "fire caulking" is, it is not required by the IRC. BTW, NEVER, EVER caulk between the firestop and the chimney pipe UNLESS the listed instructions specifically allow it. Otherwise, you could cause the chase to overheat. Now, since the plywood decking extends over to the chimney, it is reasonable to believe that combustible possessions or people could come in contact with the chimney pipe. Therefore, the chimney MUST be protected by a barrier. This can be as simple as 1/4" plywood or T-ply. Since you must have an insulation shield as well as a contact/ impact barrier, why not just sheath over the framing from the attic floor to the roof deck, thereby making it "vertical fireblocking"? This is the best solution in the attic but the lower firestop is still wrong. Even if this house has one floor and that is a off the base of a trayed ceiling somehow, the firestop still should be on the underside.

Originally Posted by Jerry Peck

You would be correct if that was an attic which had different ceiling heights over different areas, however, that appears to have walls on all four sides, which means it is just dropped down like a soffit.

That looks to be on an outside wall.

That makes that done incorrectly and the firestopping should be level with the ceiling.

I thought that this may be a tray ceiling. If so, it would seem that fire-stopping at that level would be ok, other than Bob's comments about a barrier. If it is a tray ceiling and fire-stopping is required at the attic floor level, then they would have to construct a floor over to the chimney and install fire-stopping a couple feet above fire-stopping. It would be easier to build a chase in the attic.

Originally Posted by Mark Reinmiller

I thought that this may be a tray ceiling.

If that is a tray ceiling ... that is one heck of a deep tray down to that firestopping at the chimney ... that and other parts in the photo cause me to think that it is not a tray ceiling, or if it is (and not as deep as that firestopping) then the firestopping is still in the wrong place.

Even a chase needs to be fireblocked at the floor and ceiling levels ... unless the chase itself is rated, not just wrapped in OSB (there may be an exception for less than two stories fora chase and fireblocking, but I'd have to look that up).

Based on the pictures I don't see a problem. Fire blocking, in this instance, is supposed to cut off fire from spreading from an enclosed vertical space to an enclosed horizontal space. The chase containing the flue is the vertical space, the attic is the horizontal space, and the metal stop acts as the fire stop, therefore there is no code violation. See IRC R302.11 and R1003.19.

The purpose of fire blocking is to prevent fire from spreading through the concealed spaces of any assembly in the building... In your case concealed space was created (between sheetrock and OSB) when OSB was installed in the attic. So by dividing framing cavities into separate compartments, slowing the passage of flames and combustion air, but around the chimney in your case that cavity is open. You have to fire block the cavity between your ceiling joist near the pipe, so if the fire breaks inside ceiling cavity, the fire cannot enter attic space.

Here is a sketch of what he wants you to do to prevent the fire spread. I hope it helps.

Attic Fire Block.jpg

Good luck

Originally Posted by Thom Huggett

Based on the pictures I don't see a problem. Fire blocking, in this instance, is supposed to cut off fire from spreading from an enclosed vertical space to an enclosed horizontal space. The chase containing the flue is the vertical space, the attic is the horizontal space, and the metal stop acts as the fire stop, therefore there is no code violation. See IRC R302.11 and R1003.19.

The code violation is the remaining vertical chase above the fireblocking before it gets to the horizontal attic space.

I inspect in GA, Atlanta and surroundings. What I have seen for perhaps a decade or longer, and is possibly what this inspector is referring to, is the chase around the visible fireplace flue needs to be sheathed. I see this universally done in all residential new construction and again, have seen it for over 10+ years. When I enter an attic of somewhat newer construction, I never see the chimney flue, it is always encased with OSB. I have never tried to code verify it as, again, it is universally done around here.

Originally Posted by Gregory Levitt

The purpose of fire blocking is to prevent fire from spreading through the concealed spaces of any assembly in the building... In your case concealed space was created (between sheetrock and OSB) when OSB was installed in the attic. So by dividing framing cavities into separate compartments, slowing the passage of flames and combustion air, but around the chimney in your case that cavity is open. You have to fire block the cavity between your ceiling joist near the pipe, so if the fire breaks inside ceiling cavity, the fire cannot enter attic space.

Here is a sketch of what he wants you to do to prevent the fire spread. I hope it helps.

Attic Fire Block.jpg

Good luck

This drawing illustrates and excellent way to burn the house down. You are recommending packing insulation against the chimney then encapsulating the heat trapped in the joist bay. You can NOT pack ANYTHING into a stated clearance. You can NOT put combustible material, such as OSB, encroaching on a stated clearance. The only thing that can be put in the position the OSB is shown in this drawing would be a listed firestop but ONLY if there is no firestop on the underside of those joists. You cannot trap the heat in there. You can NOT caulk between a listed firestop and the chimney unless it is expressly permitted in the listed instructions. I don't know where you got this drawing but it is dangerous. If you've actually used this as a recommendation to people you need to send certified letters ret. recpt. informing them it is a fire hazard and to remove it at once. This is a recipe for disaster. If the chimney pipe is exposed in the attic, you would actually need either an attic insulation shield to keep the insulation off the chimney and let it breathe or install vertical fireblocking, which would also address the impact protection requirement.

Originally Posted by Gregory Levitt

The purpose of fire blocking is to prevent fire from spreading through the concealed spaces of any assembly in the building... In your case concealed space was created (between sheetrock and OSB) when OSB was installed in the attic. So by dividing framing cavities into separate compartments, slowing the passage of flames and combustion air, but around the chimney in your case that cavity is open. You have to fire block the cavity between your ceiling joist near the pipe, so if the fire breaks inside ceiling cavity, the fire cannot enter attic space.

Here is a sketch of what he wants you to do to prevent the fire spread. I hope it helps.

Attic Fire Block.jpg

Good luck

What made that photo, an arsonist?