"exposed" kraft faced insulation fire hazard

DIY1 · 03-10-2013, 10:58 AM

HVAC guys are running a vertical duct (supply and return) from my basement to my 2nd floor attic. It will run right along an exterior wall and be enclosed in a drywalled-in vertical soffit. My question is how do I insulate the exterior wall cavity (behind the duct)? Would the metal ducts touching the kraft faced insulation be enough for fire protection (in lieu of drywall)?

The only other thing I can think of is to use unfaced insulation and put up some 6 mil poly as a vapor barrier (instead of the kraft facing).

DIY1 · 03-10-2013, 06:02 PM

I ended up putting drywall behind the ducts because I didn't want to take any chances with the inspector. But while I was researching I came across some very conflicting info on adding 6 mil poly over top of kraft faced insulation: Some were adamant not to, and some were adamant that you're supposed to. Some were against kraft facing in general. What's the final verdict? I trust buildingscience.com but I can't really find their opinion on it.

joecaption · 03-10-2013, 06:09 PM

Go back and add your location to your profile, yes it makes a differance.
Just go to quick links to edit.

Nailbags · 03-10-2013, 10:30 PM

Unless your running a blast furnace then their is zero chance of a fire. from HVAC Duct work. think about it? Homes would be exploding in balls of fire every day if that was the case. second you don't put a vapor barirrior over a vapor retarder. third thing ask the inspector what to do. they can offer advice.

**Gary in WA** · 03-11-2013, 12:12 AM

" Some were against kraft facing in general. What's the final verdict? I trust buildingscience.com but I can't really find their opinion on it."----------- depends on location, as Joe said. If in Zone 1-4, no vapor retarder/barrier, except 4 coastal; http://www.buildingscience.com/docum...commendations/

http://www.buildingscience.com/docum...nd-wall-design

IMO, use some PIC (foil-faced iso foamboard) behind the warm supply ducting, has a high heat factor of 200*F or something, google it. Ask local AHJ. I agree with Nailbags, no poly over kraft faced.

Gary