Fire blocking – how much, and location?


  #1  
Old 05-31-16, 06:58 AM
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Fire blocking – how much, and location?

I just finished some work in the basement, which involve removing some ceiling covering(not sure what it was, not sheet rock not wood-sort of cardboard?). All is well, except I discovered that there was no fire blocking around the chimney. The chimney is cinderblock, and used for both the furnace and the water heater (1960s house). The chimney extends through the basement ceiling then, inside a wall (one-story ranch house) and into the attic and through the roof.
My questions:
1) where can I place the fire blocking – at the ceiling of the basement, or at the attic?
2) how thick does it have to be, and of what material? In other words, if sheet rock how thick, if wood how thick?
3) would I be able to fill in the edges at the chimney with a product like "Great Stuff fire blocking foam".

As always, thanks in advance.
 
  #2  
Old 05-31-16, 07:49 AM
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1. You should do both locations.
2. I prefer to use strips of cement board up tight against the chimney, with any gaps caulked with fire stop caulk. You can also use sheet metal. You cannot use any combustible materials normally approved for firestopping, like plywood, 2by or OSB as 2" clearance from chimney to combustible material must be maintained.
3. No, you cannot use foam for this, as convenient as it would be. The foam is approved only for sealing small gaps and penetrations in firestops.

Hope this helps, good luck with your project.
 
  #3  
Old 06-01-16, 08:32 AM
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Thanks for the info. Cement board it will be. (I wasn't aware of the 2" from chimney rule-makes sense.)While some of the framing is 3" away, the fireblock would(of course) be touching the chimney)

A follow up question:
At some point in the 60+ year history of the house, somebody ran wiring up the chase-some BX, some Romex. They are tight to the framing, and (from what I can see)not within 2" of the chimney.
Can I just notch the cement board around the wiring, and fill around the notches with with the fire block caulk?

Thanks again!
 
  #4  
Old 06-01-16, 12:32 PM
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Yes, just cut a notch and seal it up with the caulk.
 
  #5  
Old 06-02-16, 06:42 AM
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Thanks again! (and again..and again for the minimum # of characters)
 
 

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