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Nola_Gal 07-19-2011 06:59 AM

Foamboard in Attic?
I live in a hot and humid climate in an old, old house. Right now I have probably close to R-40 in the attic with kraft paper facing down to the living area.

Unfortunately, I'm realizing that the this hasn't created much of an air barrier, especially considering that the house is balloon framed and has numerous cavities over closets etc. Most of the walls are plaster and lath. All of the ceilings were replaced with sheetrock. On the interior, I've been caulking and foaming all the cracks and openings I can find (around vents, pipes, doors, windows, along top of picture molding etc.)

What I'd like to do now is use foamboard (foamular or something like it) in the attic. I'm thinking that I could pull back the fiberglass, cut the foam to fit the joist cavity, caulk or foam it to seal it, then put the fiberglass back on top.

Does this sound reasonable? Would it meet code? I've read that for interior installation it has to be covered with plywood or sheetrock. Would that apply in the attic?

I can't afford spray foam and I think while it may take many weekends to accomplish, this I could do myself. Any info would be appreciated!


AGWhitehouse 07-19-2011 09:43 AM

The 2009 International Building Code does not allow exposed foam within an attic space without an approved thermal barrier (sheetrock, plywood, etc.). Fiberglass batt. would not suffice as a thermal barrier.

I would suggest laying tyvek over the top of all your fiberglass batt insulation. It will provide you with an air barrier (if you tape the joints) that will boost the effectiveness of the R-40 you already have. Doing the foam technique won't give you the best bang for your buck. The tyvek will.

Don't use plastic though! You need to use a vapor breathable membrane (>10 perms minimum). Tyvek has >50 perms and is an approved air barrier.

Nola_Gal 07-19-2011 04:09 PM

Thank you! I had a feeling that was the case but wasn't sure. The Tyvek seems like it will be much easier as well. :thumbsup:

Gary in WA 07-22-2011 08:17 PM

I'd start by air sealing the attic, remove the facing from the insulation, or turn it over so the facing is up, add Typar- rather than Tyvek- less permeable, which you want. Then air seal the crawl space or basement to stop the "stack" effect.


Nola_Gal 07-22-2011 09:30 PM

Sounds good. I will be calling around tomorrow looking for Typar.

I live in the upstairs part of what is now a split level house. When originally built, the downstairs was a framed in but unfinished 'above ground basement' (raised cottage?). After I bought it about 10 years ago, I had the downstairs built out and it is well insulated and pretty tight.

What I did find was that just above the picture molding (which is in the hallway and most most rooms) there was a gap where the plaster didn't meet the molding. I have about 75% of that caulked now and will finish it this weekend along with the other random openings around pipes and vents.

In the attic, I found I have cavities (dropped soffits?) that you could raise a small family in! :eek: Right now they are covered over with the insulation so I didn't see them until I started pulling it back. Should I do anything to seal those or will the insulation and the typar take care of that?

Thanks again.

Gary in WA 07-23-2011 08:55 PM

Any attic chase, horizontal or vertical, should be blocked with insulation to prevent convective air loops or air movement. Batts in a plastic bag, rock wool folded, etc..... more reading for you on stack effect:


And air sealing:

Stop all air leaks first, then Typar, make sure you have the minimum venting for your roof;


TrapperL 07-23-2011 11:00 PM

Nola Gal, if the quest is to lower the utility bill, consider having the attic space sprayed with a radiant barrier paint. I've inspected homes while the outside temp was over 100F and it was reasonably cool in the attic. The stuff really works as advertised. It eliminates the need for thick insulation. It also does not compromise any moisture issues. I assume it is a high humidity area where you live. If so and you have central A/C, have a licensed A/C tech install a fresh air line from the outside to the return air. It will push any humidity out of the house, balance the air pressure in the house, and bring in fresh air. Usually a 6" line will provide enough air to accomplish the goal.

AGWhitehouse 07-24-2011 01:14 PM


Originally Posted by GBR in WA (Post 691665)
I'd start by air sealing the attic, remove the facing from the insulation, or turn it over so the facing is up, add Typar- rather than Tyvek- less permeable, which you want. Then air seal the crawl space or basement to stop the "stack" effect.


The difference between Typar and Tyvek is negligable for this application. The vapor perm rating of Tyvek is 5 times that of typar which will be good for the ability of the ceiling to dry. Both systems are certified air barriers which is what this applications needs. So go with whichever is cheaper at your local store. Why do you suggest removing the facing and turning it up? your article notes that whether it is up or down is ok as long as it isn't on both sides. Seems like alot of extra work for no gain.

Gary in WA 07-24-2011 04:24 PM

In her cooling climate the ceiling would be much colder than the attic with more moisture in the warm air. Any moisture through the housewrap from the attic would condense on the vapor retarder facing paper at the ceiling, going from warm to cold, hence turn the paper up, to stop the moisture at the warmer attic (from going through the insulation, also condensing). The Typar is tighter/less perms than Tyvek to better stop moisture vapor (molecules way smaller than air) going to the cooler ceiling. In hot climates, vapor retarders go outboard of the cooling living space- paper facing down toward the crawl floor/covered dirt, exterior walls foil-faced foam board outboard of sheathing, and paper facing up in attic.
Vapor diffusion retarders,pp.2, vapor pressure differentials, pp.6;


AGWhitehouse 07-24-2011 09:16 PM

I understand that it is better to have a vapor barrier on the exterior side in climates like hers, but your posted article (the atlanta one) didn't say it needed to be remedied. Did you read it? It said it can be at the interior, exterior, or none, but never both.

If the existing system has the vapor barrier at the inside face and they've had no issues with condensation then I see no need to completely dismantle it and TRY to rebuild it. I say "try" because Typar is still permeable enough to let in the vapors and you will never seal an attic space tight with a retrofit application.

My suggestion is to leave what exists alone and add unfaced batts and tyvek. When moisture gets in (and it will) you want it to have a quick way out. Tyvek is very permeable with moisture but will greatly reduce the air movement through the batts.

Gary in WA 07-25-2011 10:31 PM

Yes, she could leave the facing down. It will be colder touching the cooled ceiling, condensing any moisture coming through the housewrap, wetting the insulation there. If it was near the housewrap, it would be insulated and closer to the temp. of the attic warm air, stopping the moisture before it gets to the insulation keeping it drier. Wet insulation degrades the R-value:

I personally would use Typar just because it is 5 times less permeable for moisture to get through. Why would you want 5 times more moisture in your insulation? Or 5 times easier for moisture to get to your insulation?

Atlanta, with 1667 cooling degree days was the closest one from BSC for her area, 2655 cooling degree days, about 60% more.


AGWhitehouse 07-26-2011 07:28 AM


Originally Posted by GBR in WA (Post 693667)
I personally would use Typar just because it is 5 times less permeable for moisture to get through. Why would you want 5 times more moisture in your insulation? Or 5 times easier for moisture to get to your insulation?

You're assuming a perfect installation of a vapor retarder in an existing attic over the top of existing insulation...That's pretty much impossible. The only way to effectively create this barrier would be to remove the roof sheathing at the eaves so you could properly seal the edges of the membrane. Based on that you need to assume moisture IS going to get in, so by putting a membrane that restricts its ability to get out you will be tempting the insulation to be more moisture laden than with Tyvek. A relatively negligable difference, but a difference none the less.

It's all relative in reality...if 1x moisture gets in with your retrofit system, then 1x will be dried off at night and during cool periods. If 5x moisture gets in with my idea, then 5x will be dried off at night and during cool periods. If condensation is a real issue in this case, the OP would have posted about stained ceilings and drippage. All i'm saying is you're presenting an awful lot of HOT and SWEATY work (it's an attic in the South!) for no noticeable gains.

Nola_Gal 07-27-2011 09:34 PM

Progress being made...
just wanted to check in and let you know I'm still following the thread and doing a lot of the reading from the sites listed. I probably won't be back in the attic for more sealing until this weekend.

One question about the openings and soffits in the attic...I've seen pictures showing how to use fiberglass in plastic bags to seal openings in the attic, but at least one of my openings is huge...I'll post a picture this weekend when I get up there, but it's probably at least 3'x4' and parts are probably 4'-5' deep. I think it runs between the hall bath and the utility room where the washer/dryer are located. There are some plumbing pipes that run through it and I think also the gas line. (The dryer vents directly to the exterior wall and not through this opening.) It butts up against the chimney chase (chimney not in use).

I guess what I'm getting at is that I could probably fill several large black plastic garbage bags with fiberglass to fill it in but I want to make sure that's what you mean. I could also use the smaller filled bags to seal off the openings to the wall cavities the empty into this space, stuff/fluff unfaced R-30 down there to fill it up and then and then just close it off at the attic floor level.

I know a picture will probably help you visualize it better than my description. I don't want to exaggerate too much, but this would have been a great house to use as a safe house.

I will go back to reading. I think I get the concept of the stack effect, though I have to think of it backwards in my case in the south. Just started reading about convective loops and know that understanding that concept will help me understand the fix for all of these secret spaces that I'm finding! :detective::detective:

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