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redwood99 05-18-2008 09:32 AM

Retrofit to Super Insulate Walls?
If I have a house with 2 x 4 studs and R-11 insulation, and I want to get those walls to say, R-20, are there any established techniques?

I was considering the following:
-Remove old sheetrock and replace 50 year old insulation
-Add a layer of OSB
-Add a layer of 2" EPS like Formular or similar
-Add another layer of OSB
-Either finish the OSB (probably not good looking), or add another layer of sheetrock.

The house is small - like 1100 s.f. and about 60 years old. If I can't bring it up to ultra-efficiency sort of standards, I don't want it. This would be part of a total gut job.

Dumb idea? Better ways to do this?

clasact 05-18-2008 09:54 AM

your best bet is your First choice remove the Sheetrock and replace the insulation and while your at it reseal around your windows and doors and electrical outlets you could also add a layer of foam board in their.The other option would be to remove the Sheetrock and have either blown in or foam insulation put in

redwood99 05-18-2008 10:05 AM

I'm just guessing though that with 3-1/2" studs, there is only so much insulation you can pack in there, and it won't get anywhere near R-20. And, I think if you compress say 6" batts to fit, you lose the insulating value?

clasact 05-18-2008 10:12 AM

true if you compress in to much you lose what your trying to accomplish thats why I put the insulation between the studs the a layer of foam board with foil backing on just like the drywall then the drywall.Also look at the outside as far as siding or whatever to outer coat is you may be able to increase your R factor their to

AtlanticWBConst. 05-18-2008 10:24 AM

Consider spray Foam Insulation over fiberglass. The R-value is greater per thickness (It ranges 2 to 3 times greater than most other insulation materials of the same thickness).

In addition, it eliminates drafts.

Some information:


redwood99 05-18-2008 05:36 PM

Ok - - some good tips there, and thanks for the info on foam. I somewhat wanted to avoid that very high price of the spray-in foam. And, where I am located there are not usually any "specialty" contractors, or firms that do highly specific applications like that. I prefer mundane technologies that are more easily contracted for labor.

So, assuming it's not completely "crazy" to apply a second wall sandwich over the first one, I have worked with rigid EPS and one thing I never found was a good adhesive for that stuff. I tried contact cement once and it burnt right through the foam!

Anyone know what adhesive is used to make SIPs? I would imagine the same would work for this application?

krankykitty 05-19-2008 01:04 AM


I don't know if this applies to your house... but my 75 year old house has tongue and groove walls. Oddly, the walls are covered with sheetrock in 1 room (keep thinking about tearing the sheetrock down, but I am also wondering why it is there in the first place... but I digress...)

In any case, if your walls are pretty solid, spray foam insulation can be added by drilling holes in the wall (I removed some wide crown molding so I wouldn't have to patch holes) and shooting expanding foam in. It worked well in my drafty bedroom. I can't swear it will work well everywhere.

There are a couple of disadvantages.

Depending on what is in your walls, if studs are in the way, etc, there can be voids the foam doesn't fill.

The other one is a biggie, and a big reason people swear off this... if you get too vigorous shooting foam in (usually hoping to avoid leaving voids) the foam can expand so much it pops sheetrock right off the wall. Sounds crazy, but I actually had a friend do this... iI thought it was an urban legend right up until then.

But, if you are going to gut the rooms anyway, spray foam insulation works great... and has the benefit if being good for sealing around windows and doors.

There are contractors who will do this work, but I did my own. I had a pretty accurate idea of how my walls are built from another one I had taken apart. So I calculated the volume of space in between each of my studs. Then I got hold of the foam manufacturer to find out how much the foam usually expands. Turns out this is dependent on temperature. So, as silly as this sounds, I borrowed a (sorry, I don't know what you call it) spray meter thing with a gauge on it showing how much liquid, in gallons, you sprayed from a friend. (A lot of contractors come on here, hopefully someone knows what that widget is called.) In any case, I sprayed the crap into a couple half gallon milk cartons, and waited to see how it would expand.

It was a warm day, and it expanded a LOT.

But once I figured out how volume sprayed was related to the volume it filled, I was good to go. I converted the spaces in the wall to, you guessed it, gallons, and kept an eye on the meter thing while I sprayed into the holes.

I did have one "oops" where some of it expanded right out of the hole. If you try this on your own, tape some paper and such around that hole, and throw a tarp on the floor just in case. The stuff sticks to everything, and is almost impossible to clean up.

My buddy's sprayer had replaceable plastic tips for the sprayer. Make sure you have some extras if you use a two part system like I did, cause if you stop spaying for longer than about 30 sec, the stuff hardens in the tip.

The whole deal, including cleaning up the oops, took a long afternoon. And it really seems to have helped the draftyness in my bedroom.

Like I said, not sure if it applies to you, but it's just a thought.

Good luck :)

jeffa 11-14-2010 09:08 PM

I think best way is first to yank off drywall, get good vapor barrier, frame in another wall inside, with stud offset from original wall. Then insulate interior framing. Drywall back up. Have to be handy w/ electrical cause you'll have to move boxes. Not a big deal.

Overall a big job though. Room by room, wall by wall.

make sure first that roof is squared away - most important.

Wha ty face is what whole country faces. White elephant energy hog buildings from sea to shining sea.

Also, don't know what you have on exterior, but if siding or if needs replaced sometime, you could wrap, seal, put 1/2" to 3/4" foam on outside whne you do it, and then use perhaps insulating siding (R3 or so) .

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