# Should there be a vapor barier in attic where walls are?



## Red Squirrel (Jun 29, 2009)

I was up in my attic removing a vent pipe for a roof vent that will be getting removed and I was unable to get the vent completely out, a section goes down a wall and has one screw, just to tease me, that's way beyond reach. So I built a box around it mostly for safety reasons (very sharp metal) and wrapped the whole thing up in vapor barrier to avoid air from going in/out of the pipe/wall that's been cut out. While doing this I noticed that none of the wall has vapor barrier over it tapped to the vapor barrier of the ceiling of both sides. I can see the top header and it's "naked". Isin't this a huge heat loss? Wood is not 100% air tight... or is it? Or is it air tight enough that it does not matter?

It would be a huge painful job to do as I'd have to do one joist section at a time, and being in there for more than 10 minutes is really hard on the knees. So probably wont bother either way, but just curious.

I'm also going to be getting the attic blown with cellulose.


----------



## joecaption (Nov 30, 2011)

There are no visable headers in an attic, you my be talking about the top plates.

If there going to adding insulation there needs to be foam baffles added, all holes where wiring or plumbing was run, all the light and fan ceiling fixtures need to be air sealed before any insulation goes in.


----------



## Red Squirrel (Jun 29, 2009)

Yeah it's the top plates I meant, but still, if I was to drill a hole into that, I could see down the wall. So by not having a vapor barrier isin't air seeping through the wood, or between the ceiling drywall and wood? The wires don't have any kind of seal either, at least the one that I saw, which is on an outside wall.


----------



## jklingel (Dec 21, 2008)

Wood is an air barrier, and is vapor open somewhat, which you want. The gaps are a problem; seal every gap you can find. You probably don't NEED a vapor barrier, though one may not hurt. It depends on where you are and if you will run air conditioning. Air seal.


----------



## Red Squirrel (Jun 29, 2009)

Ah ok, so the wood is sufficient then, though the electrical should be sealed up, which is not in my case.


----------



## jklingel (Dec 21, 2008)

Wood is a plenty good air barrier. Thorsten Chlupp, and I am sure others, uses plywood as his ONLY interior air barrier. He does not use a vapor barrier (unless building inside the city; long story, but our building department is slow to accept new information). The plywood is placed on the outside of the inner wall in a double-stud wall system. The wall plywood continues up to meet the ceiling plywood, giving a continuous air sealing layer; all joints are taped. This method leaves the inner wall available to run electrical and the odd pipe, without penetrating the air barrier. Holes and cracks are killers. A 1 square inch hole will let as much moisture through (via air) as will diffuse through AT LEAST one full sheet or sheet rock; some say several sheets.


----------



## Windows on Wash (Aug 30, 2011)

I would prefer to air seal all the top plates and penetrations with something like foam or sealant rather than deal with the vapor barrier.

Most vapor movement is on bulk air transfer vs. diffusion. Stop the air movement, you stop 99% of the moisture.


----------



## gregzoll (Dec 25, 2006)

Red, you know what GBR is going to tell you, and it is the same site that we have hashed over and over.


----------



## Red Squirrel (Jun 29, 2009)

Windows on Wash said:


> I would prefer to air seal all the top plates and penetrations with something like foam or sealant rather than deal with the vapor barrier.
> 
> Most vapor movement is on bulk air transfer vs. diffusion. Stop the air movement, you stop 99% of the moisture.


Yeah that would make more sense, I was originally wondering if the whole thing should be covered, and not just penetrations. 

When you say moisture, what is that referring to? Moisture from the house getting into the attic and causing frost? I'm more worried about heat loss, but guess that has merit too. If it was not so hard to move around in there I'd go and caulk all the openings, at least the ones I can reach. Guess I could also remove the switch plates and other indoor penetrations and seal from there. But not as ideal as sealing from the top.


----------



## Gary in WA (Mar 11, 2009)

LOL, second time today someone answered for me..... gotten to know me pretty well, eh? The other time I was simply giving information to the OP on different ventilation options.

RS, I would canned foam the ceiling/wall joints of the drywall because it lets moisture through because of the stack effect from pressurizing the room. 1/16" gap between drywall/framing degrades insulation. With no vapor barrier there, the drywall alone is acting as your air barrier. Have you seen signs of exfiltration of your (paid-for) heated air at the baseboards:http://www.homeenergy.org/show/article/nav/troubleshooting/page/2/id/1360

If easy, pull the baseboard trim and air-seal the bottom edge of drywall at the knee wall (so important, even required in our codes now), #6: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec002_par021.htm

Foam/caulk any joints you can reach to allow air movement, they are numerous: http://www.conservationtechnology.com/building_design.html#AirLeakagePathways

Gary
P.S. You two should play the lotto, I'm thinking of the winning number.....LOL.


----------

