Insulation question

[mithesaint]

I'm in the process of finishing my basement, and found a deal on insulation, but I'm not sure if this will work.

I'm insulating the walls, and the studs are 16" on center. The cavity is approx 11" deep. Lowes has R-30 on sale, but it's unfaced. Since the cavity is deeper than the insulation, will the insulation sag over time if it's unfaced? I don't need a vapor barrier, but I don't want the insulation to sag either. The stud wall is 2x4's with a space behind them for septic pipes etc, so only the front 3.5 inches of insulation will be in contact with wood. The rest will be floating in the air basically.

Thanks.

 

[Swedishchef]

Is it fiberglass insulation? If so, I believe it will sag. ROxul on the other hand tends to be more rigid but I am certain it too would sag over time.

 

[Frozen Canuck]

I suggest you use insulation stays. They are essentially long pins with a base that can be glued to a wall (used mostly in commercial work with foam panels).

Most batt products will sag (fallout) when half or less than is involved in contact with the studs. R 30 batts should be 7-8" thick & your studs are 3.5".

If you can't find a local source look into masonry supply houses as the mason's are usually the ones applying the foam. Typical between a block wall & a brick veneer.

 

[Highbeam]

Use faced batts. R-19 batted, faced, FG insulation will mostly be contained by the 2x4 studs but will hang out the back a little. It is cheap at about 35 cents a square foot. You don't need R-38 in a basement wall. You do need facing to keep your batts in place.

I am doing the same thing right now in my pole barn. I have 2x6 framed walls with offset from the outside sheathing by 2.5". The facing is doing a fine job at keeping the batts up. Over time..... who knows.

Since you have 11", you could run back and forth behind the studs with string stapling it to the back of the studs for a little extra support.

 

[woodgeek]

I don't like FG in a basement app. I'd at least use some rigid foam against concrete, taped along the seams, and keep the FG inside that. Or, just skip the FG and run with the foam.

 

[mithesaint]

Thanks frozen canuck. That was my back up plan, and I think I'm gonna do it that way. Just need to track some down.

High beam - The R-30 was only about $0.46 / sq ft, and I'm trying to insulate as much as possible. That wall is on the windy side of the house, and I'm trying to create a space that takes a minimum of energy to heat. Granted, only the top three feet or so is above ground, but the top 5 feet will be affected by frost, so I'm trying to keep it as warm as possible.

woodgeek - I already have foamboard against the wall, and will be keeping the fiberglass inside of that. That wall will have an R value of almost 40 by the time I'm done.

Thanks.

 

[Seasoned Oak]

I don't like FG in a basement app. I'd at least use some rigid foam against concrete, taped along the seams, and keep the FG inside that. Or, just skip the FG and run with the foam.

Im with you Wood Geek, Id skip the FG altogether in a basement as well and go RIDGID FOAM all the way,its the perfect place for it. No thermal breaks to boot

 

[semipro]

If you do use FB batts in a basement most experts recommend not using faced batts. The facing acts as a vapor retarder and can result in water being trapped in the wall space. Most recommend foam and/or unfaced FB or Roxul batts with mold resistant drywall and latex paint (no oil or wall paper).

 

[woodgeek]

Gotta agree with highbeam, not clear why you need R-40 in a basement wall. If they are below grade, they run a lot warmer than above grade walls, so, your effort is like making an R-80+ above grade wall. And since R-value is reciprocal, R-40 is not 4 times the savings of R-10 (a typical code number) versus uninsulated, instead it is negligible savings. My guess is that little airleaks around the sill, or detailing of insulation on the rim joists, or losses out the slab would have a much larger impact than going from R-20 to R-40 in a basement wall.

IOW, unless this is very recent construction with underslab insulation, thermal breaks between the slab and wall, careful detailing of the rim area thermal bridges, then it will still not be an ultra low loss space. It is like superinsulating one of four walls in a room, the heat just goes through other paths. In a retrofit situation, an inch of exterior foam and stucco to cover the above grade areas would have a much higher impact.

All basements also eventually get wet, pipes leak, laundry machines malfunction, etc. And someone will be unhappy with all that wet FG down there doing no good. If the foamboard is R-10 without bridges, I'd call it good enough and put my attention elsewhere in the envelope. IF you wanted to overkill it, bring the foamboard up to R-20 and be smug about having the most insulated basement walls in OH.

 

[maple1]

I'm also not sure about having piping on the cold side of R-30? Might there be a chance of some freezing? Plus being hard to get at if a cleanout is needed?

 

[Swedishchef]

Gotta agree with highbeam, not clear why you need R-40 in a basement wall. If they are below grade, they run a lot warmer than above grade walls, so, your effort is like making an R-80+ above grade wall. And since R-value is reciprocal, R-40 is not 4 times the savings of R-10 (a typical code number) versus uninsulated, instead it is negligible savings.

The new building code in certain provinces in Canada requires that basement walls be insulated top to bottom with R19 (in some zones). It has gone nuts. R50 attic, R29 above grade walls.

Personally I believe insulation should be top to bottom on a basement wall. Where I live the front goes atleast 4 feet in the ground....

Andrew

 

[woodgeek]

Yeah, but the frost line is a lot deeper in parts of Canada than in OH. Concrete conducts, so, I am not saying just do the top half (on the interior). Some folks down here are getting great outcomes insulating the exterior.

 

[Swedishchef]

Yeah, but the frost line is a lot deeper in parts of Canada than in OH. Concrete conducts, so, I am not saying just do the top half (on the interior). Some folks down here are getting great outcomes insulating the exterior.

The new thing around here is using ICFs. They can range from R18 to R35. If you can keep your concrete warm, it is better than preventing air/cold air leaks from the inside outward. A buddy of mine spray foamed the entire house. Man oh man it is efficient and air tight ( needs a nice air exchanger).

 

[mithesaint]

Gotta agree with highbeam, not clear why you need R-40 in a basement wall. If they are below grade, they run a lot warmer than above grade walls, so, your effort is like making an R-80+ above grade wall. And since R-value is reciprocal, R-40 is not 4 times the savings of R-10 (a typical code number) versus uninsulated, instead it is negligible savings. My guess is that little airleaks around the sill, or detailing of insulation on the rim joists, or losses out the slab would have a much larger impact than going from R-20 to R-40 in a basement wall.

IOW, unless this is very recent construction with underslab insulation, thermal breaks between the slab and wall, careful detailing of the rim area thermal bridges, then it will still not be an ultra low loss space. It is like superinsulating one of four walls in a room, the heat just goes through other paths. In a retrofit situation, an inch of exterior foam and stucco to cover the above grade areas would have a much higher impact.

All basements also eventually get wet, pipes leak, laundry machines malfunction, etc. And someone will be unhappy with all that wet FG down there doing no good. If the foamboard is R-10 without bridges, I'd call it good enough and put my attention elsewhere in the envelope. IF you wanted to overkill it, bring the foamboard up to R-20 and be smug about having the most insulated basement walls in OH.

Totally agree that it's overkill. I don't need that much insulation in that wall, and I am going to lose heat elsewhere in the room, probably through the slab. I was going with the R-30 in the wall for two reasons: I have the space in the wall, and it's not that much more expensive. If there was a significant price difference, I would put R-15 or R-19 and call it a day. I already have an inch of exterior foam, 1.5 inches of interior foam and I've insulated and sealed the joist spaces and the sill, so I figured it would potentially be worth it in the long run. The difference between R-19 and the R-30 I bought was $10 for the entire wall. Will it ever pay back? I don't know. I'm considering returning the R-30 and getting faced R-19 to make installation easier. The rest of the walls will get R-13 so I know it won't make a huge difference to have R-30 in that one wall. It just kills me to purposely leave a space in a wall cavity uninsulated.

Maple1 - the pipe behind the wall is the main drain leading to the septic. The cleanout is in a different part of the basement, and I'm not worried about it freezing due to almost 3 inches of foam and a concrete wall between the pipe and the outdoors. No water pipes in that area.

Thanks.

 

[velvetfoot]

I wonder if you should put slits in the facing-I think the latest is no vapor barriers in basements, but it seems to change from year to year.

What I'd be interested in is if you're going to insulate the floor in any way?

(I'm kind of fixing up the basement, slowly and have insulated most of the walls with foam and covered with drywall. Of course, with an insulated basement, a heat pump hot water heater won't work as well. Then too, space had to be made in the garage for the truck and guess where that stuff goes-the basement. Then, it has to be heated. ayi yai yai (sp?) Sorry for the digression.)

 

[woodgeek]

Don't mean to bust you....we all do weird things when presented with a weird feature of our houses.

It sounds like there is a stud wall a foot out from the foam on the concrete. Weird. Who built it like that? Can you rip it out, tapcon some wood strapping to the wall through the foam, and put drywall on the strapping? Then at least you'd have a larger room, what 10-15 sq ft?? A $1000 value on resale??

 

[velvetfoot]

I think it's kind of like a pipe chase.

 

[woodgeek]

I got that. Unless there is a 6" pipe running horizontal across the middle of the whole wall, I would consider a 'bump out' around the pipe, or make a real closet that has the pipe in the head space or whatever. Always want more open floorspace and closets. An big cavity is useless, filled with FG or not.

If the pipes are low, do a half wall with a 12" deep shelf along the top.

 

[mithesaint]

Woodgeek - there is a 6 inch pipe running horizontally across the middle of the wall. It also runs slightly downhill. Too low for a closet, too high for a shelf. Figured that just building the wall to hide the pipe was best. It still leaves a 25x25 room so l'm not worried about the lost sq ft.