Do I need a vapor barrier in an attic with a vent?


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Old 05-16-14, 08:12 PM
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Do I need a vapor barrier in an attic with a vent?

I'm planning on putting down two layers of unfaced R19 pink insulation in the attic. Do I need to have a vapor barrier underneath the insulation between it and the "warm" house? Or should the small vent on one side of the attic be adequate moisture ventilation?

Thanks
 
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Old 05-16-14, 08:35 PM
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I would say no vapor barrier. Around here, no one puts vapor barrier on ceilings. Here is an article to support that idea.

Q&A: Ceiling Vapor Barrier
 
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Old 05-16-14, 08:46 PM
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Thanks for the link. NJ seems to be in the 4500-8000 heating degree days so the author suggests latex ceiling paint should be an adequate vapor retarded. And the logic in the article makes sense.

Thanks again

And I'm still open to other suggestions, recommendations or reasonings.
 
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Old 05-17-14, 03:46 AM
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You will note in Joe's article an emphasis on the air barrier everywhere. Houses have all kinds of air leaks and extreme effort should be made to seal as many as possible. His point is, air leaks will bypass any vapor barrier so if you seal the leaks you don't need the VB. BUT, you do need to seal the leaks. Below is a link to help you identify hidden leaks.

As an added thought, I'm not fond of r-19 pink. Fiberglass insulation performs poorly in attics when not enclosed on all 6 sides. The reason it is popular is price, but we all know what buying the cheapest material gets us. Look at Roxul or consider blowing in cellulose. In all cases you will want baffles in each rafter bay which drop down to cover the end of the insulation. This blocks incoming wind from washing right through the insulation as well as keeping the insulation out of the soffits.

One of the downfalls of fg insulation in an attic is that the incoming cold winter air flows right down to the drywall reducing the effective r-value significantly. Using a very dense insulation helps to prevent this.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
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Old 05-17-14, 05:27 AM
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The filling of cracks is a tough one. The attic floors/(second floor ceiling) is lath and plaster. The plaster is almost completely cracked and falling down onto the cheap "drop ceiling" my grandmother installed just underneath the plaster a very long time ago (although it's a pretty solid drop ceiling, unlike the drop ceilings in offices).

We're in the process of ripping down the drop ceiling, the falling plaster and all of the lath and replacing it with sheetrock. But it could take years (this is very much a work in progress house) to get to it all, because the living room, dining room and kitchen are all on the schedule to be renovated first (and those will take a long time, the work moves at a glacial pace doing it ourselves).

I'm now thinking of installing insulation supports, then strips of plastic as a vapor barrier, then the insulation. This way we get some vapor barrier, but also when we do finally get around to ripping down the ceiling in the other bedrooms we don't have fiberglass falling down on us as well.

As for the pink insulation, we've got 15+ brand new rolls that were bought years ago and we've just been storing. So this is just as much about using/getting rid of them as it is about re-insulating the attic.

Thanks for the advice
 
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Old 05-17-14, 08:53 AM
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The deteriorated plaster and the suspended ceiling sound like a real problem. I'll try to explain.

The air barrier, vapor barrier and thermal barrier should all be in the same plane and IN CONTACT with each other. The drop ceilings will leak air and from the sound of it so will the plaster. Somewhere above that the moist air will encounter a surface cold enough to form condensation. Even if you take steps to seal from above, the air that gets through will be a problem.

Understand I can't see what is actually there so just doing my best to provide guidance.

Let's see if others jump in with any thoughts.

Bud
 
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Old 05-17-14, 04:02 PM
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So it sounds like this will be more of a problem in winter? Or will my central air cause the same problem in reverse during summer? This can't really be a "new problem" because the house has been the same way for 20+ (maybe?) years.

The only thing that has changed is this (late) winter, we removed all of the blown-in insulation that was in the attic. Now I know the next thing you'll say is "you may have been better off keeping the blown-in insulation for its insulation." But that's cause you didn't see what we had up there lol. It was ugly, and couldn't have been healthy.

I could attempt to take down all of the drop ceiling and lath/plaster sooner rather than later and throw up some sheet rock before moving on to the next rooms. I'm not sure if it would get done before it gets really hot this summer though. What about buying alot of spray foam and foaming the lath from the the top? As a temporary solution.
 
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Old 05-17-14, 05:25 PM
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Spray foam is kind of permanent and the cans wouldn't cover very well. They do make DIY kits for spray-in foam, but it would all be removed when the plaster was ultimately removed.

Summer is less of an issue with both air leakage and condensation.

If you cut those strips of plastic so they came up and over each joist where you could run a bead of silicone to join them and/or loop up and over several joists to form a better air seal, it would be better.

Yes I have seen ugly old insulation and yes I do recommend it be removed.

But do air seal all major leakage paths.

Bud
 
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Old 05-17-14, 07:40 PM
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Ok, cool. At least it's not as big of a problem during the summer. Taking care of it in the fall is much more doable.

I was about to say it'll just be plastic up and over the joints and then insulation until the fall. Then I remember the other portion of this project is nailing up new 2x6's against the original 2x4's joists that are running lengthwise across the bedrooms (15'-20') and sagging in the middle (nothing is easy with this house).

So instead I'm guessing it'll be easy strips between the joists to hold the insulation up while we rip down the lath and plaster and nail up new 2x6's and then a full sheet of plastic underneath the joists before we sheet rock.

Btw I think I read I should use 6 mil plastic?

Thanks for the help
 
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Old 05-18-14, 04:40 AM
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A little extra complication there.
Only one vapor barrier. A gap between two provides a place for moisture to be trapped.
A 2x4 ceiling on a house with plaster and lathe doesn't sound right over that gap. Plaster implies an older home and 2x4 as a truss would be a newer home.

I'm trying to think of a better approach that would minimize your steps and I'm not doing very well. If you cobble in the plastic vapor barrier and then have to come back and sister larger ceiling joists to the existing 2x4, that seems like a headache.

Confirm the age of the house? Confirm the span those 2x4's are supporting? And perhaps a picture or two of that attic.

Bud
 
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Old 05-18-14, 05:29 AM
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I guess I was over estimating the size of the second bedroom (that we're not currently working on now), because I thought it was longer. It turns out both bedrooms are only about 13' long. I don't know an accurate age of the house, maybe 1920s or 30s? My grandmother moved here in the 1970 maybe?

Makes sense about having two vapor barriers. I guess we'll just deal with some falling insulation, or temporarily put up insulation supports while we take down the ceilings.

I'm uploading some pictures, the first is the current room we're working on with the 2x6's up against the 2x4's.

The second is the 2x4's with the lath/plaster. The plaster looks in decent condition there but you can kind of see the sag in the joists. Unfortunately I just finished re-insulating the duct work and running new flex duct (which is why some of the taping isn't finished), so I couldn't get a wide open picture of the joists.

Third picture is the only vent we have in the attic. I post this because you mentioned baffles being needed at the edge of the roof joists. I'm not sure if we even have vents in the roof overhang. Is that possible? My grandmother (a very long time ago) installed brown tin "trim" over the real trim on the outside of the house. And either the contractors covered the vents entirely, or there weren't any to begin with...

Fourth picture is the drop(-in) ceiling. It's actually nailed up to 1x3 boards which are screwed into the lath/plaster.

Thanks man
 
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Old 05-18-14, 09:26 AM
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The staple-up tile ceilings were a common quick fix back then.

If you tuck unfaced batts into each joist cavity they would be easy to remove later when the old plaster has to come out. Although, taking a second look, I'm not sure what you have for a span between joists, complicated by the 2x6 sistered along side. With a 2x4 and 2x6 sistered side by side you get an odd space to fill and when insulating, those details count. What is your space between joists with the 2x6 added?

Take a look into the soffit area to see what is there. I suspect there never were any vents. If wood, then some can be cust in.

Bud
 
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Old 05-19-14, 04:55 AM
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There's 13" of space between the joists (essentially 14.5" on-center from the 2x4 to the 2x6). As I said the I guess we would have to trim an inch or two of insulation on every roll. It will be a major pain, especially because it is either cut too wide or too narrow.

At this point I'm thinking about not insulating this summer. Just let it go until we can take the ceiling down in the fall...It would make it easier to wire lights and outlets from the attic and we wouldn't have to deal with itchy fiberglass dust falling on us in addition to everything else. It's just inefficient cooling it, but the central air never had a problem cooling the second floor, it's downstairs that's the problem.

Adding vents is also an option. The one "how-to" I found googling, said just adding them to the backside of the house should be sufficient?

I feel like this should be added to every single post on this website, but it's crazy how one little job morphs into a huge never ending project if you want to do everything right.

Btw, just thought I would throw this out there. Other than the crappy blown-in insulation in the attic, the rest of the house has/had ZERO insulation. It's just the brick exterior, then a couple inches of air gap, those large square stones you see in the vent picture, then an inch of plaster(?). So Idk if some of what I'm seeing in the attic was designed that way? The other part of our project is attaching a couple layers of 2x4s (3 horizontal ones at the top, middle and bottom of the room. Then vertical ones 16" on center, both layers laid "flat" on the wall) to the walls so that we can add insulation.
 
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Old 05-19-14, 06:35 AM
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The other thing I saw in another post that I might benefit from now is a radiant barrier? It seems to take the place of a baffle sort of, and the only thing I would have to deal with is blocking insulation from falling down into the vent soffit.
 
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Old 05-19-14, 07:20 AM
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"I feel like this should be added to every single post on this website, but it's crazy how one little job morphs into a huge never ending project if you want to do everything right."
Certainly not all DIY jobs turn out that way, but it is a case of accumulating knowledge and experience to know when that is going to happen.

I'll add a couple of links on bricks, they are a pain as they need ventilation and sometimes heat. Remove either in an attempt to make the home more energy efficient and risk problems with the bricks. These articles will help a lot. It is not a case that you can't do it, just do it right.
BSD-106: Understanding Vapor Barriers — Building Science Information
BSI-047: Thick as a Brick — Building Science Information

I worked on an attic where they had sistered 2x8's against 2x6's and same dimensions as yours. They had stuffed the r-19 into the smaller space and the results were about zero insulation. Blown-in cellulose is about the perfect choice once the ceiling below and other work is complete. If you fill to the top of the 2x6 you can then utilize those batts over the top. To utilize the batts with the space you have and fit it in properly it will take a ton of detailing.
Example: Cut the current batts down by 1.5" so they fit tight between the 2x4 and the 2x6, then trim the piece you removed to fill the small space above the 2x4 and be neat. If you decide to cut, post back and I will make it easier.

I'll let you read.

Bud
 
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Old 05-19-14, 04:37 PM
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Interesting articles, I like the one on bricks especially, thanks. There are a few sections where the bricks are on unheated areas, I'll have to check them out tomorrow to see their current condition.

A couple of things, of course I did forget to say that most of the second floor exterior is actually stucco, it's the first floor that's brick. I just repainted the stucco with three coats of elastomeric paint last summer.

Second, the vapor barrier article was good, although I had trouble trying to match up the different scenarios to my own. There may be a couple more layers between the stucco/brick and the inner wall that I don't know about.

It also recommended against polyurethane vapor barriers in air conditioned buildings which this is a few months a year. I'm starting to think no vapor barrier is necessary since there wasn't one originally? Looking at the map in the first article, I'm right on the line between cold and mixed-humid in NJ, although probably more in the cold area.

What you're saying about the stuffing the isolation in, is that it removes all of the air from it, which is actually what insulates and not the fiberglass material itself, correct? I probably will end up cutting it, maybe just once though, and then fitting the extra piece right on top of the 2x4 without cutting it down to the same height.

Thanks man
 
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Old 05-19-14, 05:39 PM
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If you choose to not trim the small piece that will fit on top of the 2x4 you will be stuffing a 3.5" piece into a 2" deep space. It will bulge up and create a void on each side by lifting the second layer of insulation. small job to trim that to a good fit.

As an energy auditor I often get to look at the end results with an infrared camera and it doesn't take much of a gap to create an air path and significantly reduce the insulation performance of a job.

If you study those articles you will know more about bricks than I do.

Bud
 
 

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