Sealing around flue in attic


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Old 07-08-15, 11:04 AM
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Sealing around flue in attic

Attached are pic's of what I am working with. Very tight. Would be very hard to caulk around the flue after putting down flashing. Wondering if I could add a 2x6 block to the open side making a box around the flue in the rafter and then putting the flashing on top of the box. Name:  0708151343.jpg
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Old 07-08-15, 12:30 PM
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It's a little unclear to me what you ate trying to do, so I apologize if this response isn't applicable. .....

First thing: what is this venting? You really should have a minimum of 1" clearance from combustibles all the way around the pipe. It may not be wise to keep the pipe so tight to the drywall in the photo

Secondly: pipe flashing is meant to use on the outside where it penetrates the building (ie roof or sidewall). This pipe isn't terminating into the attic space is it?

Third: if you are just looking to air seal the pipe around the drywall opening you should use a fire rated caulk or foam.....
 
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Old 07-08-15, 12:51 PM
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It is the flue from the furnace which is in the basement. It goes up through a closet in the second floor up into the attic behind a kneewall. We just bought the house but it was probably done back in the 90's. House was built in 38. I am trying to air seal it. I am cutting aluminum flashing that will butt up against the flue then I will seal it with high temp caulk. Then I add a sheet metal damn going around the flue up about a foot that will keep the insulation I am adding an inch away from the flue.

Instead of putting the flashing down by the drywall I want to build a box by putting a 2x8 block on the open side which will build a box around the flue. Then I can put the flashing on top and have easier access to caulk.
 
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Old 07-08-15, 12:54 PM
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And what's up with the lack of insulation?
There should be at least R-40 as a bare min. in that attic in your area.
 
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Old 07-08-15, 12:54 PM
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Just found what I want to do. Page 32 on this link below, Metal Chimney Vent Chase. Bud9051 gave me the link. (Thanks)

http://www.buildingscience.com/docum...-sealing-guide
 
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Old 07-08-15, 12:58 PM
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Yea, I am air sealing before adding the insulation. Just bought the house, a cape cod that had R-11 insulation sorta hanging on the roof rafters. Put it right over the ridge vent and gable vents. Had to remove the moldy crap.
 
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Old 07-08-15, 02:05 PM
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But just to be clear. ....the pipe is venting to the outside right? That's what my biggest concern was. .......if it is venting into the attic then you will have major issues!
 
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Old 07-08-15, 02:11 PM
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Ha, no it goes up and out the roof.
 
 

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