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jayzlookz 09-01-2012 09:51 AM

Basement foamboard help/questions
Hello. I live in GA and I am looking at finishing my dry basement. When I bought the house I had the builder frame the basment for me and run the electrical. Now that I see the benefits of foamboard I am having problems trying to glue it on the walls. The distance of the framing to the concrete is only an 1" in most areas. I have tried using the 3/4" foamboard but I had to cut it in half for it to fit between the framing studs. After I put the glue on the board I could not get the foamboard through the studs without the glue coming off on the studs since it was so tight trying to squeeze it through the studs. Are there any other alternatives outside of tearing the framing down and putting up the foamboard? I have talked to a few other local people and they are saying as long as my wall is dry to just but up faced batts and as long as it isn't touching the concrete I will be fine. Is this true? Thanks for any advice.

notmrjohn 09-01-2012 10:23 AM


Originally Posted by jayzlookz (Post 1000956)
...just but up faced batts and as long as it isn't touching the concrete I will be fine. Is this true?

Can you put the glue on the wall? You mite have to cut your panels narrower, into thirds. Lots more seams to tape but... Lines of glue towards left edge, hold left side of panel out, right against wall, slide over, push left side in, right out, squirt glue in along right.You really only need enuff glue to hold panel snug to wall. If you got bad bow out towards center of panel, could poke a hole use a bent wire or flat metal to pull the panel out some and squirt glue in, then tape least you have some space, some still nail frame or furring directly to wall with foam between studs some do put up the foam and then nail thru to wall, punching nice holes thru the barrier. Mite have to cut panels shorter too. You may be down there a while.
Sure woulda been nice to have wider space, it would also help in insulating basement. Your panels, impervious panels right? are more of a moisture barrier than insulation. Once you got that up all nice and snug and taped you put unfaced bats between the studs. That's your insulation. The more space behind studs the thicker bat can be, they shouldn't touch the foam panels. No vapor barrier on inside or outside of stud wall. You do not want to trap moisture between the outer and inner walls or inside inner wall. Then cover with dry wall. If you are going to panel wall, mud over nails/screws, but don't tape joints, prime and 1 qwick coat paint.
Idea is, panels resist outside moisture, inside moisture can pass from room thru wall, but can also pass back instead of getting trapped.

Gary in WA 09-01-2012 07:07 PM

The adhesive pattern keeps the air from the concrete wall:

The thickness of foamboard is important for dew-point condensation but needs to be vapor permeable;

What is your Zone?


jayzlookz 09-02-2012 08:04 AM

Thanks for the responses. I'm in zone 3A. I will try to cut the foamboard into 1/4 pieces and see if that works easier for glueing. My wall is 9 1/2 feet tall, do I need to go all the way to the top? Lastly, in some of the corners the framing is right on the wall. What can I do about that since foamboard won't fit in there?

md2lgyk 09-02-2012 09:22 AM

The framing should not touch the walls anywhere. If it does, it needs to be removed and correctly reinstalled.

notmrjohn 09-02-2012 11:58 AM

jay, foam hasto completly cover wall, all the way to top, bottom, side to side, no gaps, no holes, no open seams, caulk or spray foam arond any pipes, wires etc. Otherwise its like closing a window on a cold day but leaving the door open.
md sed it,"The framing should not touch the walls anywhere." Not only can you not get foam back there, the frame itself acts as a conductor of temperature and moisture. The frame should not touch foam, insulation in frame should not touch foam. You want an air gap between basement wall and interior FOAM wall. This is not same as any air gap between foam and basement and serves different purpose. ideally there is no gap between foam and concrete but..., proper adhesive pattern does not keep air from wall, it prevents air from circulating top to bottom causing condensation on structural wood members. Over stating the case, we don't care how much air or moisture is behind foam, just so long as it doesn't get into room or con dense on anything it could damage, like wooden structural members.
The foam should NOT be vapor permiable, we are trying to keep water vapor fro coming thru basement wall and into basement.
GBR, let's you and me re-read that 2nd link, the "News story#2: basement walls don't need to dry to the interior" part, I mighta missed something and at 1st glance it seems to contradict it self. But here's the main part, the artical starts by quoting Dr.Lstiburek, THE expert and author of THE book, "“It is important that interior insulation ... [on basement walls] be... vapor permeable)" But way down at bottom it says, ' Lstiburek now says that the advice he gave in the Builder’s Guide was wrong. Lstiburek said, “I made a mistake. It’s OK for the concrete to be wet. The concrete doesn’t have to dry to the inside.”
The idea of permeable barrier was that the concrete had to be dry, you had to get the water out of the concrete wall. But author of article made a good point, other side of wall is soil, full of moisture, without a vapor barrier the wall just wicks the moisture out of soil and into basement. The only way to prevent that is barrier on outside of wall. Without an interior barrier basement wall is trying to suck intire earth dry and pump the water into basement.
jay like I sed B4, tape every one of those seams between panels. I don't wanna have to come all the way over to your place for a drink after your basement sucked the earth dry.

jayzlookz 09-03-2012 12:03 AM

Thanks of the helpful advice. This really sucks because just looking at my basement it seems that I have to remove all of the pre-existing studs and move the electrical in order to get the foamboard behind it and the corners off the wall. I cannot believe the builder framed so close to the wall and that foamboard is the only good way to prevent moisture. More money, jeez.

notmrjohn 09-03-2012 09:42 AM

I'd forgotten about that electrical. Exactly what do you mean? Conduit or wiring directly on basement walls or in framing? Course we now know it can't be on walls. If there is enuff room behind your new frame to get fastening tool back there, run and fasten wiring other utilities on back side instead of in frame. If insulation is no thicker than frame you won't have slice and poke it around wiring. Without hiring tiny little guys with tiny little tools i can't see how you'd get back there. Depending on how much space you're willing to give up,you could leave a narrow work gallery behind there. Maybe a strip of thin plywood fastened to side of stud, projecting back a bit, with hole in that end for wire.
"... cannot believe the builder framed so close to th'e wall..." There's still some just fastening furring strips to basement wall, then plastic sheeting foam or furring over sheet or foam, poking nice holes thru it. Many still think that foam is primarily acting as thermel insulation. Foam is not the only good way, but here it is easiest effective way. imagine how non easy some of the others would be. More money? Where? Oh, I see.

Gary in WA 09-03-2012 07:40 PM

R-5 continuous or footnote "f"- none, depends on location:

Sorry to confuse anyone as I was... my thought I was trying to bring across was the thickness of foam is important to limit condensation in the cavity; if not thick enough, the framing/cavity insulation will get wet from excessive basement humidity. The air space behind cavity insulation (air permeable- fiberglass, cellulose, etc) will negate some of the R-value unless the air is PERFECTLY still (requires sill-sealer under the existing mudsill). Remember to fire-stop walls (spaces between foam board/framing) every 10' of length and to the floor cavities above per code;

Poly sheeting adhered to the concrete could work but use foam board to cover or you may still get condensation from the basement air on it. "A" here; http://www.buildingfoundation.umn.ed...jectReview.htm

I wouldn't use foil-faced polyiso because the foil may react to the alkali (and deteriorate) in newer concrete releasing it from the glue still attached to the concrete wall (I'm still researching that point). Then you would have unfaced polyiso that absorbs 7-1/2 times more water than XPS. Your R-value would quickly go south as in Table #7:
I'd be concerned the water would wick/gravity down and puddle under the framing adding mold. Maybe not, per BSC ; page 60- if thick enough to warm cavity above dew-point with any wood framing; Also, polyiso is on pages 37, 40, 53 and 57. The faced PIC behind XPS would be problem free in my book, personally.
You for sure want to keep all basement air from the concrete, Wall#3, page9-14 here, XPS did well;


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