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Old 10-12-2010, 10:51 PM   #1
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rigid foam insulation on interior


Hey folks. We have an 1880's balloon framed fixer upper that has never been insulated. It was an abandoned crack house when we bought it, so in need of a lot of work. We're in Pennsylvania.

Very structurally sound, but not very pretty yet. We've gutted most of it (while living in it--NOT recommended), and have removed the plaster and lath. Now it's time to insulate and drywall.

The external wall studs are a full 2 3/4 x 3 3/4 inches, and most stud bays are 13 inches wide. Diagonally run 1 inch wood sheathing boards are 1 inch thick, Some sort of asphalt shingle looking siding on that, then aluminum siding. Trying to insulate as well as possible, but also have budget restraints.

I've been thinking of R-13 or R-15 batts in the bays, then possibly using 1/2 inch--or even 1 inch--rigid foam on the inside. Taping seams, then covering with drywall. This could get me R-17 to R-20 with the 2x4 studs and also act as a thermal break for the wood. Removing siding and adding foam sheathing isn't an option

Early in the planning stage, but many questions.

1. Is it OK to use rigid foam on the inside?

2. If so, should I use a 6-mil vapor barrier or would this allow water to collect between it and the panel?

3. Is the panel "hard" enough for drywall, or would the finished wall feel "mushy"?

Thanks for all replies--Bill




Last edited by itin1200; 10-13-2010 at 01:15 AM. Reason: typo
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Old 10-13-2010, 07:28 PM   #2
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rigid foam insulation on interior


no need for a vapor barrier, thats what the ridged foam will be, assuming you tape it up properly.

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Old 10-13-2010, 07:46 PM   #3
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rigid foam insulation on interior


Hey sounds like my central Pennsylvania project!

I'm no expert in this but I have read that different rigid foams have very different abilities to block vapor.
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Old 10-14-2010, 02:53 AM   #4
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rigid foam insulation on interior


I'd install something good in the walls, like cellulose, cotton or mineral (rock) wool. Leave the fiberglass at the store. I don't know if the foam right under the sheet rock is a good idea. My gut says it will compress and then the wall will get spongy/sloppy. My bother-in-law hangs drywall for a living and insists on gluing the drywall to the studs so it is a solid wall. Any way to fir out w/ 2x2s, either parallel to or perpendicular to the studs, then insulate between them with "something good"? More time, but likely less $$ that the foam. Besides, foams tend to give of gasses, hence they are usually used on the outside (to poison your neighbors' air). Most foams are not "vapor barriers" (unless foiled faced) but will retard vapor. That is probably all you need, though. Myself? Fir it out, and use the Airtight Drywall Approach to let the wall breathe to the inside. No foam.
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Old 10-14-2010, 07:15 AM   #5
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Don't use fiberglass. Dense pack it. Its worth additional cost now for savings forever. Its true that you'd need to double check the foam for being a vapor barrier.
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Old 10-14-2010, 07:34 AM   #6
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Is there a way to create a thermal break on the warm side of the studs without (a) longterm outgassing, or (b) building a second wall.

Anybody familiar with this aerogel stuff in the real world?
http://www.jetsongreen.com/2010/02/a...nsulation.html
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Old 10-14-2010, 12:28 PM   #7
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Anybody familiar with this aerogel stuff in the real world?
http://www.jetsongreen.com/2010/02/a...nsulation.html
Wow. Pretty amazing stuff, if real. I'd check on buildingscience and/or greenbuildingadvisor, etc.
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Old 10-14-2010, 01:26 PM   #8
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rigid foam insulation on interior


If you have it stripped to the bones and it was me, I would get a wet cellulose spray into the unusual open joist spaces and then cut off the excess. Apply the cellulose after you are doee with any electrical, etc. Far better than any fiberglass. You could possibly do it yourself if you rent the equipment and find the cellulose, but a contractor could do it quicker and cheaper in the end. Cover with a vapor barrier. Just make sure you have everything open an accessible and just stand back out of the way.

You can then use an untaped extruded foam on the exterior to eliminate the "thermal short circuiting" caused by the wood joists.

You may have to look into any fire stops for your type of framing, the cellulose could eliminate them since it is superior to fiberglass. - Depends on local codes.

DIY does not mean that you have to do everything yourself if there are areas where you can get something better, faster and cheaper and dedicate your time to other things that are better suited to the project.

Dick
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Old 10-14-2010, 01:58 PM   #9
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rigid foam insulation on interior


OP said they did not want to disturb the exterior. Unless you REALLY trust that exterior is shedding water properly, I would not use cellulose in the wall cavities. If there is doubt on this score, I'd rather have the cavities full of closed cell foam, or roxul, or fiberglass, in that order of preference, to try to prevent wetting the cavitiy and helping it dry. Cellulose does dry as well, I hear. If upfront price is really important fiberglass may be the winner. But care is needed to go a really good job on installation, without leaving any gaps or creating any compression.
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Old 10-14-2010, 03:24 PM   #10
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rigid foam insulation on interior


I have seen enough of fiberglass and moisture after over 1000 damage claims from Katrina. Fiberglass technically does not absorb moisture, but it holds it and never dries out unless it is removed and physically disturbed in the presence of a heat source (or disposed of in a land fill). I saw many homes with 6"-12" of water flooding and no roof damage that had the sheetrock (previously "drywall") ceilings falling in because of the moisture weight. Obviously, all of the walls had to to stripped and removed and the entire interior re-done all because of a few inches of water a few days of heat. It hurts to see the results due to the preformance of the highly promoted products.

Since fiberglass is not as fireproof (melts first) and has less insulating value, I have to recognize that I made a few mistakes of my own projects in the past. The total concept of batts and fitting into joist spaces where there is always air leakage as evidenced by the dark areas seems to be pretty odd.

If the exterior does not want to be disturbed, rigid can be used as an extra interior barrier (and eliminator of the stud "thermally short circuiting") and then be covered with an interior "vapor barrier". I use the quotes because a vapor barrier is not absolute but is only a specific number decided upon after many months of argument. When it comes to poly, for a given type of plastic, it depends on the thickness, but of course the definers never contemplated the cuts and nailing.screwing. Poly vapor barriers are commonly destroyed by slitting.

I suspect this particular project may not be suitably open and accessible enough to a sub-contractor application, other DIY options are always available.

Dick
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Old 10-14-2010, 03:33 PM   #11
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rigid foam insulation on interior


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Originally Posted by steveel View Post
OP said they did not want to disturb the exterior. Unless you REALLY trust that exterior is shedding water properly, I would not use cellulose in the wall cavities. If there is doubt on this score, I'd rather have the cavities full of closed cell foam, or roxul, or fiberglass, in that order of preference, to try to prevent wetting the cavitiy and helping it dry. Cellulose does not dry as well, I hear. If upfront price is really important fiberglass may be the winner. But care is needed to go a really good job on installation, without leaving any gaps or creating any compression.

[Edit: Oops, originally I neglected to add the "not", where it is now bold above.]

Dick, your experience of fiberglass in katrina's aftermath is interesting, but you neglected to compare it to similar installations of cellulose in the same environment. Also, unless I'm missing something, the OP is in central PA, which has little history with katrina type events so I'm not sure how relevant those anecdotes are.

My question is: if you fill side by side cavities with fiberglass and cellulose in central PA, and then add equal amounts of water, which will dry faster and with less damage overall? I don't know the answer from any personal experience, but I've always heard that properly installed fiberglass dries faster than properly installed cellulose under otherwise identical conditions. Does anybody know of tests? Gary, you listening?

PS yes, I agree that just askign this question instead of fixing the exterior weather barrier is less than ideal, but hey.... it's an imperfect world

Last edited by steveel; 10-14-2010 at 03:41 PM.
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Old 10-14-2010, 04:00 PM   #12
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rigid foam insulation on interior


Itin: I don't think choosing insulation based on possible massive water intrusion is exactly the best strategy. My thoughts are (no tests done, no experience seeing disasters) that if you get massive water intrusion with any insulation you are in deep shinkie. Maybe closed cell foam would survive the best, but you'd still have to strip the walls and wait for a long time for the wood to dry, IMO. If your exterior is likely to leak, then not fixing that is not an option; sorry about that. I think the idea of wet packed cellulose is a good idea, but if I did not mention it before, you probably do not want a true vapor barrier in PA. The Airtight Drywall Approach is probably the best option. Buildingscience.com has maps of where to/where not to, but true VBs are probably not recommended for PA. BTW: What is under your alum siding is probably good old 15 pound felt paper, STILL one of the best sub-siding materials available. Good luck. j
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Old 10-14-2010, 04:05 PM   #13
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rigid foam insulation on interior


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Originally Posted by jklingel View Post
What is under your alum siding is probably good old 15 pound felt paper, STILL one of the best sub-siding materials available.

I agree with jklingel's post, and just wanted to add that the above part is true assuming the paper was properly installed with correct attention to flashing details. As we all know, corner cutting is not just a modern day problem. Also, massive water is one thing, and a little bit on a regular basis faster than stuff dries out is another

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Old 10-14-2010, 04:14 PM   #14
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rigid foam insulation on interior


steveel -

I omitted my other work. Before and after Katrina, I did examinations of home problems in a similar cold climate that had moisture and mold problems and could pin down the problems with a poke or two of my 4" long moisture probes and some past experience it was easy to find the sources. Most were due to the poorly installed windows (I have a Certification in window installation from a national association), so the source of the leak was easy and the fiberglass created an on-going problem that could never be corrected until the wall was stripped and the installation removed and replaced. The insulation with as little as 1% moisture had the insulating value that was reduced by 50%, which changed the location of the dew point in the wall and had future effects. Apparently, the exterior structure of the fiberglass has the great ability to hold water and repel additives.

I became disenchanted by the antics of the pink panthers in code writing meetings and the attempts to politically hide and possible problems. Somehow, they strangely came up with a buy pink attitude similar to the anti-China campaigns, when Buick supposedly sold as many cars in China as in the U.S. (third to Mercedes and BMW in a poor-quality oriented nation) - It is all smoke and mirrors and advertising. If you want batts, use mineral wool.

Dick

Last edited by concretemasonry; 10-14-2010 at 04:18 PM.
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Old 10-14-2010, 04:42 PM   #15
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So the windows and flashing were the real problem. we agree there.

You saw a lot of wet fiberglass in that situation. OK no argument.

QUESTION: Did you also see cellulose filled cavities around similarly leaking windows? Were they in better or worse condition, or seem to be more or less likely to become problems?

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