Interior Chase - Exiting Through Dormer - Vapor Barrier????

[BurnIt13]

I recently finished the install of my Englander 30. The stove is on the first floor and the chimney passes through an enclosed chase in the upstairs bedroom. The tricky part is that the chimney pipe exits out of the dormer in the bedroom. I'm having a hard time deciding what to do with a vapor barrier. Here is a vague pic:

(broken image removed)

The top of the pipe is exiting directly out of the roof. My concern is that if I don't install a vapor barrier, then I will get condensation on the roof and/or chimney flashing when the stove is not in use. If I do go the route of vapor barrier....then what is correct? Here are my ideas:

1. Insulate the chase framing with kraft faced R13. Is this acceptable? I would have to install some sections of wood perpendicular to the framing on to prevent the insulation from falling in right? Clearances to combustibles will be maintained but what if a piece of the fiberglass insulation ever breaks free and falls onto the pipe?

2. No insulation, install plastic sheathing on the outside of the chase framing. Worries me that some day many moons down the road a piece will break free and contact the chimney pipe.

3. No insulation but install thin sheet metal on the outside of the framing before installing the drywall. Not cheap but probably the most sturdy.

4. No vapor barrier at all...I'm just paranoid.

What do you think?

 

[Danno77]

Frame it, drywall it, make sure the chimney is sealed at the roof. Should be ok.

 

[Danno77]

I think you should throw some shelves in that cavity between the chase and the closet.

 

[BurnIt13]

Frame it, drywall it, make sure the chimney is sealed at the roof. Should be ok.

Really? Thats what I had originally planned but is condensation an issue? I imagine for the same reason we use vapor barriers on upstairs ceilings and outside walls no? Or am I just bein paranoid?

And yes, I will be building a book case between the wall and the chase. Currently the room is gutted in preperation for the baby my wife is incubating. That "homemade dresser" you see in the picture up against the wall was actually a closet once upon a time....and will be again when I'm done with it.

 

[begreen]

The picture may not show all. Are you concerned because the storm flashing has a gap or ventilation slots and you can see a bit of daylight when you look up from the inside? It won't hurt to insulate the chase if that is the case. I don't see any need to add any more wood for the insulation though. The kraft paper faces the room. Just staple the kraft face tabs to the wood every 12". It won't go anywhere, particularly once held captive by the sheetrock.

 

[BurnIt13]

Thanks for the replies guys! My main concern is that warm, moist household air will rise and meet the cold flashing....then condense and eventually cause mold. Very similar to the effect when an attic does not have proper insulation/vapor barrier and the warm household air ends up condensing on the roof sheathing. Is the main purpose of the ventilation slots to prevent this?

I'm cautious (and probably unecessarily so) of putting insulation in between the framing. My worry is that decades from now the fiberglass may somehow lose its bond to the paper and fall inward onto the chimney pipe. But.....is that even a problem?

Or am I just WAY over analyzing this and I should just put drywall up only and forget about it?

 

[begreen]

Yes, are you an engineer? J/K

 

[BurnIt13]

Ha...is it that obvious??? I'm an electrical engineer by trade I've been fighting off the urge to install remote sensors inside the chase to monitor temperatures and humidity!

I think I'm just going to put up drywall only and forget about it. After all...the inspector signed off on it so I guess it won't be on me... Agree???

 

[begreen]

Is the storm flashing ventilated at the top, under the storm collar?

 

[oldspark]

My storm flashing is vented so I am going to insulate the chase but did not plan on a vapor barrier. Not sure if this is correct or not.

 

[begreen]

The insulation should be enough to deal with temperature differential, but it doesn't seem like it would hurt to sheath it in plastic before the drywall.

 

[BurnIt13]

Is the storm flashing ventilated at the top, under the storm collar?

Yes the flashing is ventilated below the storm collar.... ???

 

[begreen]

I would insulate it then. Mostly to avoid mold build up from condensation when the AC is running.

 

[oldspark]

You have me rethinking this, did a google and some people are using a vapor barrier, not sure that makes sense to me as the air in the chase will be warm already. Many people haveing issues but there are different building variations.

 

[begreen]

In the summer when the house AC is on and it's 90% humidity outside is when the vapor barrier would help. Think about td's wood stove condensation concerns.

 

[oldspark]

So you want the barrier on the outside or inside of the insulation in the chase?

 

[BurnIt13]

I was planing on using Kraft faced insulation. It is not a pure vapor barrier but rather a vapor retarder. Here is a good article as to why I've chosen this route:
(broken link removed)

 

[oldspark]

Be better to have it on the inside (of the chase) in the winter and on the house side in the summer correct? Not possible but that would be the ideal maybe.