So what do you do about insulating the walls in a room that’s being gutted in a 150+ year old house where the studs are really 4″ deep? If you use fiberglass, 3 1/2″ is too thin (big air gap between the face and the new sheetrock), but if you use 5 1/2″ you lose R value when you compress it to fit into the space. I’m thinking slightly compressed insulation w/o air gaps is better than uncompressed with big air gaps, but my contractor disagrees.
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spray foam.. My choice or dense pack celuliose. Fiberglas is a lousy insulator!
no problem!
Your contractor is wrong.
Frenchy is 100% correct.
Spray foam is definitely best, but sidesteps the question, and is often way too expensive for a single room. Blown cellulose of chopped FG would also be better than batts.
For the two options you presented though, you are right.
Just today, I was working a room that had been insulated only with R-11 in full 4" frame. I considered leaving it as it was, since it was only a 14 wall, and partly filled with windows.
but I took the time to check it some. The space on the outside of the wall, between FG and sheathing was cold, drafty, and WET. the cold air circulating there was not only a source of heat loss, but the dew point was maiking for a lot of condensation
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I agree fully with the blown-in stuff. But, if it is too small for blowing in, consider the following.
I read in another post some time ago (and I don't feel like fighting the search engine here) that the EFFECTIVE insulation value of "6-inch" batts put into 2x4 walls was better than the "4-inch" stuff. The higher density apparently is more than offset by better sealing of drafts.
So, easiest thing would be to get the batts used for 2x6 construction and use them.
BUT--be sure that the stud spacing equals the 16 or 24 centers for which the batts are cut. You don't want loose fits, or the cold air will just whistle around the batt.
(Oh, yes--you might be surprised at how reasonable blown-in insulation can be, even for smaller areas.)
Edited 1/9/2009 5:25 pm by JohnD1
the 5.5" is a better choice. You'll do a little better than if you used the 3.5" stuff. Of course, convincing your contractor (or even some people here) of that is another matter.
What about cutting 2" rigid foam (polyiso) to fit in between the bays? Foam the cracks, and the R value will be higher than fiberglass. A little time consuming, but I have done it in my own house and it isn't too bad. As for cutting the foam, I went to the salvation army and bought a cheap set of serrated steak knives. They made way less dust than anything else and they were 4 bucks.
I meditate, I burn candles, I drink green tea, and still I want to smack someone.
table saw works well, too.
Dan: If you lke living dangerously, grab your wife's electric caving knife out of the kitchen to cut your foam. (BSEG!)
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Dan I used to do versions of that but I found that I could use a sheetrock square and utility knife, (fresh blade not some old rat that had been used to cut tarpaper and sheetrock) score the foam and snap it. that made no mess and was a lot faster.. (hint, score the ends completely as well)
Quick and easy, use the R19 batts--but first seal the stud bays with can foam. Run a line of foam along each stud against the sheathing, and especially down near the mudsill.
You're trying to stop air infiltration.
if you where to use 2in foam and rip them to width and double up you would have you'r 4in,if it where my place i would spay foam, i did my place and not only did my gas bill go down my house is quieter then before and no drafts.jimbotg
If it's similar to the 100 year old houses I've worked on, there are plenty of gaps in the wood sheathing if there is sheathing. My last house just had siding. We just used R-13 and thought the airspace would let the wood behave as it had for the last 110 years.
I found out after a while that some areas would get water into them and the fiberglass would get wet, and stay wet for a while. I wound up removing the siding in those areas and putting up felt to protect it.
In our current 1920's house we have brick siding so things stay dry, but there are 1/4"-1/2" gaps in the wood sheathing, and the wind still blows through. We decided that spray foam was too high for our current budget so we have installed 3/4" poly foam board and foamed the cracks prior to installing R-13.
There was a suprising difference with just the foam board prior to insulating. This is a current project so the cold and wind are very apparant. The cost was more in our budget, we got R-15 effectively in the walls, and no drafts blowing through the fiberglass.
I think that this is an effective alternative bridging the cost and energy effectiveness factors.
Hope this helps,
Ott
Waters has the right idea. I've done something similar on my house and the difference is significant. Any way you can stop air movement is best.
An alternative is to install 1/2" rigid against the sheathing then install the 3-1/2" batts. Foam around the rigid would be very beneficial.
Given the small space, why not try one of the DIY spray foam kits?http://www.fomofoam.com/If not, dense-pack cellulose seems like next best option, followed by 1/2" rigid cut in place, sealed at edges w/spray foam (from can - cheap), then your 3-1/2"R values are somewhat meaningless if you have air infiltration problems...
Edited 1/10/2009 9:58 am ET by GraniteStater
Hmm ... I dunno ... sometimes e.g. R-13 insulation lofts more than 3 1/2 inches. But to answer your question ... an R-19 would be better than an R-13 ... denser means better air leakage control.
But ... I've heard people talk about the notion that a 5 1/2" batt in a 4" cavity might exert too much stress on the drywall. Don't think I agree, though. Compressing 1 1/2" is really pretty small. I'd do it. My guess is you'll be at maybe R-15 w/ the R-19 Batt.
Altrnatives would be the cellulose ... wet applied. Or foam if you can afford it.