When working with faced fiberglass insulation, how does one best slice a batt lengthwise so there is a staple tab remaining of the facing, for insulating bays narrower than the common bays?
I am asking because I haven’t yet worked with kraft-faced fiberglass, but am doing a takeoff and planning an installation in an unfinished (but studwalled) basement.
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Replies
Man - if you need that Q answered for an estimate - you need ... oh never mind... :-)
Get one of those utility knives with the long retractable blade - you know the blade snaps off every 3/4 of an inch or so. Cut by eye. It doesn't take too long to get good at it. If that doesn't work for you, use a 2x4 as a "rip fence".
Generally though, I've found that I can hire an insulation contractor to do a house for maybe $200 more than I can buy the material. The big contractors get volume discounts and it's hard to compete with.
BTW - my first job in construction was as an insulator - not necessarily proud of the fact... How long ago? I think gas was thirty-some cents a gallon ;-)
There is no such thing as an insulation subcontractor here where I am. One must do everything oneself. We are in a village of 3000 with a 50 mile ride to the nearest Wal-Mart.
I am trying to understand how the 50 or so stud cavities of odd narrower width are going to be insulated in a Superior Walls basement. We can buy faced rolls at the right length to do 14.5 and 22.5 cavity width (ours are 22.5) but am just wondering how it will go when we need to rip a 22.5 roll to do a cavity of, say, 17 wide, and still have an edge tab for stapling.
I am sure that cutting insulation is easy with the right knife, a good blade, and the right work table. I am just looking to hear about the technique of cutting and getting a new staple edge at the cut.
My experience ... I could be doing it wrong ...
You don't get a new staple flange when you rip it to width. So you rip slightly wider than you need, staple one side, and let friction hold it in place. Better to rip a half inch too wide than a half inch too narrow.
Easiest way to cut kraft faced insulation is with a sharp utility knife on a wood surface. You can do it on concrete but it eats up the blade. The trick is to mash the insulation flat with your knife hand and the handle of the knife while you draw the blade down the paper. If the blade is sharp and you mash it flat enough, it cuts easily and cleanly.
I have seena utility knife in Lowes that is made specifically for cutting insulation. It has a wide plastic guard on the handle, like a hand guard on a sword, that helps to mash the insulation flat. I have never seen it used so I don't know if it works, but I suspect it helps.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Oh - OK - what Ed said. When the bat is "ripped" it is only stapled on one side. If you really wanted to staple both sides you could "rip" it 1" wider than necessary and then compression fit the bat and staple the cut edge. Now someone is gonna chime in that the batt would be compressed and that would reduce the R-value, however as always, one has to insert a little common sense.
Would compressing a bat to fit in smaller bay necessarily reduce the R-value? I could see if you were compressing it to a smaller thickness, but I wouldn't think that width wise would matter...
No, with standard density batts, slightly compressing the batt actually improves its per-inch R value.
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No electrons were harmed in the making of this post.
Lay the batt down on a piece of plywood. Place another piece of plywood or 1x along the line you want to cut. Press with your knee while you cut with a sharp utility knife.
Cut about an inch wider than you need, then just separate the FG from the kraft on the cut edge and staple the edge down, compressing the FG against the stud.
Or, better, don't worry about it -- just staple the FG enough to hold in place, then cover with plastic vapor barrier.
No electrons were harmed in the making of this post.
Don't use faced ins.
Then use a poly VP over entire wall.
Done.
Why so many odd sized bays Gene?
Eric
It's Never Too Late To Become What You Might Have Been
[email protected]
This is one of the worst mistakes that is commonly made when insulating basements. Poly is a vapor barrier. Basement walls are exterior clad with a vapor barrier and have huge supply of moisture outside that in the soil. If you put a vapor barrier on the inside of a basement wall, then it cannot dry to the interior or the exterior. This makes the wall intolerant to the smallest intrusion of moisture. Any leak of the exterior system or even the moisture in the basement walls from construction can cause mold growth in the stud wall.
For every person that now writes in about how they did it and didn't have a problem, I can show you a picture of ugly, ugly problems that had to be repaired by someone else that experienced what I'm talking about.
Please don't recommend this practice. It is very costly to repair this simple mistake.
thank you for the excellent question. I'm certainly no expert on the subject. These are just some of my observations.I think I've seen situations where the insulation was not stapled at all. It goes in pretty tight and seems to stay put.I've encountered situations where I've tried to figure out how to get the insulation to fit around plumbing, electrical conduit, etc. and one of the things I have to be careful about is I will try to pack it in and I think this can cause problems and maybe even push outward and put pressure on the sheetrock and result in bulging in the sheetrock.Getting to your question, all I've ever seeen is the insulation gets cut and stapled on the one side and that's it. That's just my experience.There's a lot of experience in these rooms and maybe someone else has come up with a procedure to cut the insulation a little wider, remove the fiberglass, and then have the edge you're referring to (I just haven't seen it done that way)
U R right.
Brain fart.
So is using paper faced in the same situation ok?
I would think no vapor barrier on the living side.
EricIt's Never Too Late To Become What You Might Have Been
[email protected]
To the guys who said use a plastic vapor barrier - that used to be in vogue here in NC. Then with all the paranoia about mold and trapped moisture, it is not so popular any more. Now, most everyone is back to using paper faced bats - the idea being that you really don't want to trap moisture and do want some drying to both the inside and outside.
Probably works fine in dryer climates.
PS: here is an example of the knife I said I recommended:
http://www.cleansweepsupply.com/pages/skugroup15425.html
Using a kitchen knife sounds OK, but nothing beats a razor blade.
Edited 11/3/2005 7:44 pm ET by Matt
I just bought some johns manfield insulation at Lowes (rebate of $75 for $250 purchased) and they now have "perforated" batts. THere are 2 or 3 batts in the bundle that are perforated lengthwise so it is easier to cut the batts to the necessary width. There are a couple of perforations in the batt so you can get close to the width you need. I found you still have to slice the fiberglass side with the utility knife but it I didnt need to squeeze it down with 2x4's as I usually do. There are slightly visible track marks on the insulation side that line up with the perforation lines so you can see where you are slicing. As others said, just make it slightly wider and you can still staple the sides.
Hope this helps.
If the cavity is wider than a few inches where a friction fit is OK, I have always just cut the bat about an inch wide of the cavity and loosened the FG from the facing as it was going in, so the facing can be stapled without insulation behind it. Probably not necessary, but I'm anal. (I know this because my wife and daughter remind me of it regularly!)
Same thing I do, cut it and extra inch wide and you can staple both sides.
I would think that with all those mega homes in Lake Placid there would be an insulation contractor who makes the trip. I have one that takes the ferry over here from the mainland. Their blown walls and ceilings are way better than anything I can do myself.
In cutting R-38 batts for my 2X12 rafters, I found a much easier way to cut it both horizontally and vertically. Go to a local Good Will store and get a 12" kitchen knife with a hard blade (if you've got a portable hardness tester, this will help), so it'll hold an edge, and a large comfortable wood handle. Sharpen to a razor edge on your sharpener of choice. I found that a very fine carborundum belt on my 1" tabletop belt sander would do the trick. Then, as mentioned above, I took two long pieces of plywood, put them sideways edge-to-edge with about 1/8" of space between the edges and attached them together at each end...then put this over the batt, press straight down and drew my knife between the ply edges and usually in one swipe I could get a clean cut. But the trick is to push the ply straight down and not let the batt get pushed sideways, or the cut will be uneven. And the knife will have to be resharpened every few cuts.
BruceM