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Sealing around fireplace/chimney - fire rated


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12-06-17, 10:32 AM   #1 (permalink)  
Sealing around fireplace/chimney - fire rated

I'll be installing Type X drywall in my garage in the near future and need to seal around the brick fireplace/chimney where the drywall butts up against the brick (rear face of fireplace/chimney is exposed inside garage). What is the accepted method of sealing these joints? Can I use regular caulk or do I need to use fire-block sealant? Also, there is only 2" of space between the stud wall and fireplace on the right side. Any suggestions on how to best seal the joints in this area? It's extremely tight and it probably should have been taken care of before the wall was built (I can't think of everything). Aside from removing a couple studs from the new wall, I don't see how I'm going to access such a tight space. I have access from above, so I can slide a thin strip of sheetrock down into this area, but sealing the joints along the left/right/bottom is going to be a challenge. I'm assuming it needs to be air tight to pass fire code.

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Last edited by mossman; 12-06-17 at 11:06 AM.
 
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12-06-17, 11:09 AM   #2 (permalink)  
Draft stopping and fire stopping is done along with framing, prior to your rough framing inspection or you won't pass. Generally no drywall is hung until that is completed, unless it is part of top out. And yes, if you are asking about doing the top out prior to the framing inspection, the sealant to use where the top out meets masonry must be an approved fire caulk. Depending on where you shop there are various brands.

 
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12-06-17, 11:17 AM   #3 (permalink)  
I don't believe I have any fire blocking to do. The type X is my fire wall right? As long as there are no breaks between the garage and home, which there won't be. Regardless, this is something I will definitely mention to the builder. I agree the framing should be inspected prior to hanging sheetrock. Although the one wall is existing and was not modified other than removing the siding, and the adjacent wall is accessible from the other side, so having a piece of sheetrock on one side shouldn't be a big deal should it?

They still have some truss bracing to do, so that is holding up my framing inspection.

Don't know what "top out" means.


Last edited by mossman; 12-06-17 at 11:45 AM.
 
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12-06-17, 12:29 PM   #4 (permalink)  
I just thought of something...since it's only a 2" gap, couldn't I spray fire-blocking foam in that area as opposed to gypsum board? That would serve as my fire blocking and seal tightly against the wall and brick. I can slide a piece of OSB in there as a backer (permitted by code to touch fireplace), cut a few holes in the sheetrock from the opposite side to secure the OSB to the adjacent wall, then fill the area with spray foam. I realize it may be difficult to envision what I'm talking about, so I'll post a picture later this evening.


Last edited by mossman; 12-06-17 at 01:33 PM.
 
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12-06-17, 01:52 PM   #5 (permalink)  
Here's a diagram (top view) of what I am proposing. I could also screw a piece of Type X to the OSB strip prior to wedging it in the corner. As such, the foam would simply be for sealing the edges against the fireplace and wall on the right (the foam would obviously fill the entire cavity).

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12-06-17, 03:59 PM   #6 (permalink)  
No. Foam does not take the place of approved fireblocking materials. Your "osb backer" cannot be there... it is closer than 2". Your framing pictured on either side of the word "fireplace" is also closer than 2".

See R602.8.1, R1001.15, R1001.16.

You would likely need to do it similar to the way it is illustrated here: http://www.jlconline.com/how-to/inte...nd-a-chimney_o

That link also explains where fire rated foam is usually used. The caulking you pictured could be used where your approved fireblocking material meets the masonry provided the tube says it meets R1001.16.

 
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12-06-17, 07:29 PM   #7 (permalink)  
What I read in the code is that the EDGE of sheathing can touch the masonry. I verified this with the county inspector. To be clear, the new wall is the one to the right, which meets the required 2" clearance. The other walls are original. Regardless of whether I can put the OSB backer piece in there or not and only a piece of type X, is the only acceptable way of sealing to use the fire rated caulking?

 
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12-06-17, 07:41 PM   #8 (permalink)  
Found it...R1001.11 exception 3 says combustible materials can abut the masonry as shown in Figure R1001.11, which is what I am proposing.

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12-06-17, 08:30 PM   #9 (permalink)  
Drywall or cement board then caulk the resulting gap where they meet... yes, the exception applies only if the combustible sheathing is at least 12" from the firebox.

 
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12-07-17, 05:08 AM   #10 (permalink)  
What about along the floor/slab? Do I need to install the Type X down to about 1/4" above the slab then caulk the joint all along the bottom? If so, I'll have to cut the bottom course at an angle in order to match the slope of the slab. And I won't have a nice finished/factory edge on the bottom. Not really ideal. I suppose I could install the type X so that it follows the slope of the floor, then cut the top level. Except then I'll have long butt joints in the middle of the wall. Or perhaps don't cut it level and just have un-level joints. I'll be finishing the walls anyhow, so you'd never know.

 
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12-07-17, 01:33 PM   #11 (permalink)  
This is what I'm dealing with. As you can you, I have access to the opposite side of the righthand wall. I also have access to the opposite side of the back wall, although I'd have to cut drywall, which I'd like to avoid. I think I should be able to remove the studs from the corner, nail my piece of OSB to the stud in the existing wall, screw the 2" strip of type x against the back wall, seal the perimeter, put the studs back, place full piece of type x (areas I can't reach with a screw gun will be glued). The only challenge I can anticipate is sealing the corner joint between the two piece of type X once I place the large piece. Perhaps I could apply a liberal amount of caulk or joint compound to the right side of the 2" strip after it is installed, then when I butt the large piece of sheetrock against it the caulk/joint compound will squish out and seal the joint. Any other clever ideas?

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