Hi, all. Thought I might see if someone would take a shot at this insulation question.
I’m rebuilding a set of built-in drawers in my 1939 Oregon house (wood lath and plaster, no insulation). This gives me an opportunity to slide behind that wall and install insulation. Once the built-in goes back in, there will be no easy access, so I’m wondering what a good choice for insulation material would be in this application. I’m concerned that the stuff stay in place over time… Thanks in advance for any advice.
Redm
Replies
insulate a wall behind a wall? Why not insuoate it the same way you are insulating any other wall in the house whatever that is? Simple.
What am I missing here?
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
For small areas fiberglass is probably best/simplest. But jam it in -- a double layer (two 3" batts in a 2x4 stud bay) of unfaced, eg -- and then install a plastic vapor barrier, taped around the edges.
The other option would be sheet foam, as much thickness as will fit in the wall, and foamed with canned foam around the edges and in the cracks.
red alert!Jaming doubled FG into a space reduces its effetiveness. no benefit whatsoever to doing that
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Wrong!!!
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I can't believe that DanH said that!
Believe it. Standard density FG is not at anywhere near the density needed to achieve optimal insulation value, especially if you factor in any infiltration. Probably tripling it's density would be about optimal, but double is a reasonable approximation.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Hmmm...I always thought that the insulation value was due to the air pockets, so denser would not be better. Please explain! If high density made for better insulation, wouldn't lead be a good insulator? Or just filling stud bays with sand--same as fiberglass only denser?
Dan,
Ya got any proof type references, 'cuz here's my thinking; everybody in the insulation industry knows that all the consumers know that with insulation, the bigger the R the better. Except the FG industry doesn't think they need to come out with a bigger and better version that just needs a bit more material stuffed into the same space.Since I prefer borate treated cells I don't follow FG science much, you might be right, but you haven't convinced me yet.SamT
Look at "high density" FG vs standard FG. The R value is about 50% higher for insulation that's about 3x as dense. Plus, the denser insulation better controls the infiltration problem that often torpedos FG insulation value, so the net effect of the increased density is even more."Bigger is better" when selling a house by the SF, but few potential HOs ask what R value insulation is in the walls, and the less dense stuff (whatever just meets code) is cheaper and easier to install, meaning more profit for the builder. The FG industry is happy to provide the low-density insulation as well, as it's cheaper to make, package, and ship.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
The industry CAN make denser insulation that is better, but you go WAY out on a limb to assume that by just individually jamming it into the space, you can achieve that same results that specially spun and woven at the factory materials can do.
All you achieve is creating spaces that are piunched, pulled, shoved, and have more gaps for infiltration alongside of spots that are alomost solid glas fibre and better at conduction than at insulatin.I saw a study on just this very assumption done back in the seventies. They packed 9" FG into a 5.5" space and 6" FG into a 3.5" space and measured effectiveness vs the standard and found no gain - only a waste of money. So if you are going to indict the industry on charges of ripping people off, they would certainly be amoung the first to be recommending overuseage and use of higher density, but dollar for dollar, it does not pay of and in some cases can add other problems - like how do you get the sheet rock to stay on the wall and how do you eliminate cold pockets from over-compression that adds to conductive heat loss.your assumptions on this are just that - assumptions only - with no value in this case.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
HEY!, you just had to say that and get me wondering if I'd read right somewhere in the past.
Seemed I recalled reading that a 6" batt stuffed into a 2x4 wall, tho' losing dollar value, did increase the Rvalue over a standard 3 1/2" R11 to something more but less than the R19 of the 6", but now I'm not so sure.
be now I'm wondering
September 1, 1842. Mr. Thoreau dined with us yesterday. He is a singular character — a young man with much of wild original nature still remaining in him; and so far as he is sophisticated, it is in a way and method of his own. He is as ugly as sin, long-nosed, queer-mouthed, and with uncouth and rustic, though courteous manners, corresponding very well with such an exterior. But his ugliness is of an honest and agreeable fashion, and becomes him much better than beauty. He was educated, I believe, at Cambridge, and foremerly kept school in this town; but for two or three years back, he has repudiated all regular modes of getting a living, and seems inclined to lead a sort of Indian life among civilized men — an Indian life, I mean, as respects the absence of any systematic effort for a livelihood.-Nathaniel Hawthorne, from American Notebooks
RezI was getting ready to make the same comments.And I found this on Owenings Cornerning's website."Bob writes from West Orange, New Jersey: "My friend compressed R19 fiberglass batts intended for a 2x6 wall cavity into a smaller 2x4 wall cavity. The wall is now covered with wall board. What is the effective R value of this improper installation? What problems will this cause? What do you recommend?"Answer: Stuffing a 2x4 wall with R-19 will decrease the R-Value to about R-13, so your friend will not receive the full benefit of the insulating value he or she purchased. High Density R-15 insulation would have been a better choice. The insulation shouldn’t cause any problems and replacing it will be a hassle since the cavity is already covered. With walls, we typically have only one opportunity to insulate them for maximum energy efficiency. "So what you say right is correct. But there are now higher density products that do a better job than compresing 6" into a 4" space.And Piffin's example has MUCH more compression..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I guess the other thing to factor is the cost
I was looking at the Johns Mansville r-15 not too long ago, and it wasn't anything stocked locally.
I'd have to check the number but I think it was 40% more than the standard stuff you find stocked.
-----------------------------------------------------------------------------
"If you come to a fork in the road, take it"
There ya go!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
My memory was that the R19 compressed to 3-1/2" gives you twelve point eight somethingor other is all. By buying the R-13 that is designed to be optimal in the first place, you do better than the R19 squashed.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Jaming doubled FG into a space reduces its effetiveness. no benefit whatsoever to doing that
Sure hope that's not the case, else I spent a buncha dough on densepack FG for my house for nothing.
(In point of fact, it seems to be working pretty well...set at 75, the AC doesn't run much at all in a ~2900SF 2-story on a 98-degree day, provided the damn kids don't flap the door too much.)
Jason
There is a big diff between using a product designed and formulated to be efficient for a space and misusing twice as much of a different product
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I wouldn't bother, particularly if you are in a temperate part of Oregon. The built-ins will block air infiltration. What will you gain by insulating a small section of wall? Walls are just not a major problem.
The built-in is less effective at blocking air infiltration than is intact plaster, plus air infiltration will draw dust into the drawers. At the very least there needs to be an infiltration barrier (plastic or housewrap) behind the unit.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Plastic would be a vapor barrier, and probably is not a good idea, as the moisture might condense on the surface, and puddle at the bottom. An air barrier is a decent idea, though I was assuming the plaster was going back up.
I really enjoyed all the back and forth info on insulation but....................... I recommend Cellulose blown in. Most places that sell it will let you use the machine. The advantage is you can insulate any nook or any cranny through an inch and a quarter hole in the wall. Plus Cellulose is recycled and non itchey.
Thing is that he's got the wall opened up -- nothing to retain the cells -- and only 2-3 stud bays (I'm guessing) to fill. Too small of a job to make cells very efficient, at the very least.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Thanks, DanH and all others who posted replies here. You understood the situation perfectly. I should have made it clearer that removing the built-in will give me access to about 20 feet of wall, an amount probably worth doing from an energy perspective especially since I won't be able to access it again. The discussion of the R-value of compressed fiberglass is interesting, but since the stud cavities are only covered on one surface there is no way to compress the material, even if I wanted to do so. Unfaced fiberglass is probably the material to go with, but I don't have enough experience to know if it will stay in place over time. Stapling some netting over the outer face of the studs would be extra insurance against the batts falling out of the cavities, I guess.
Again, my thanks to all.
Redm
I can't belive nobody has mentioned spray foam yet. SHAME on you. Actually Redm R value is only half the equation, air infiltration is the other biggie. The current issue touches on this a bit. You could get a foam kit for a couple hundred bucks.http://www.taunton.com/finehomebuilding/how-to/articles/best-way-to-insulate-a-rim-joist-with-expandable-foam-kit.aspx?ac=ts&ra=fp
BTW since this is a knee wall I would do the roof rafters so you dont have to insulate the floor behind the knee wall.
Your right and looking back at my comments it's probably too large and complex and wouldn't be cost effective.When I remodel and have spaces that need to be insulated I just use the appropriate material. Sometimes I just have to stuff insulation in a space and I don't worry about whether the R value is less because of how it is stuffed in there. I'm just glad that there is some kind of insulation there. I do follow rigid guidelines when installing new insulation. Thanks for your feedback and input.