attic insulation questions

[nospam.house]

I need to insulate the attic, and I have some questions/concerns I hope someone can help me out.

I have 2x6 in the attic, and it is about 80-90% covered with really old what appears to be unfaced R19 fiberglass batts. It looks very dirty (I replaced the roof so lots of dust falled on it) and aged. Some of it is only half the height of the 2x6.

I've gotten some bids, and it is about $1400 for blow-in fiberglass, and $1100 for blow-in cellulose of R30. All of them said I can leave what I have up there, and just blow on top of it. (I am in San Francisco area and the recommended attic is R38)

1) Is it good to blow on top of the old/aged/molded fiberglass? Should I remove it and start clean? Does it insulate better that way?

2) fiberglass guys claims that cellulose will rot the wiring and plumbing if it get wet, and will degrade. It is also very dusty which is a big concern for me. Cellulose guy says fiberglass has health risks. I have heating duct in the attic, and I am concerned about the fiberglass, or the cellulose dust being drawn into the duct and gets everywhere. Fiberglass guy says because my house is relatively old (1950ish), he wasn't sure if I have tube/wire electrical wire up there and cellulose is not safe. The cellulose guy said I don't need to worry about it.

I am thinking about replacing the fiberglass wrapping around my heating duct with more modern ones to seal off any gaps before I blow the insulation up there. Right now I am leaning toward fiberglass as it won't age or settle, and if I get a roof leak it won't get destroyed. But how do I know if the installer won't fluff the blow-in?

3) The cellulose guy quoted me 8.1" for R30. I just don't like that 8.1". I mean how the hell is he going to make sure that the attic is 8.1, not 8, or 7.5? by eye balling it? Seems like I am paying by the inch yet I have no easy way of verifying it. (I can't really walk in the attic after it's done..) One of the fiberglass guy said they've done this for so long, that they just know if it's 12" or not. Is it true? Or do they basically do "ah, it looks like 12", done, when in fact, it may very well be just 10")

Which weights more? Cellulose or fiberglass? If I go with R38 (doesn't add that much to the cost), Is the weight of all that insulation cause any problem with the ceiling in the long run?

Thanks!

Raymond

[Steve Barker]

Cellulose is the only way to go. Attics or walls. It's fire retardant, and has more r value per inch. And there's no reason for it to get wet, but if it does, it just dries out. As a matter of fact, it is applied wet.

check out

[Joseph Meehan]

Both are fine.

Beware of any contractor who knocks the other product.

I would choose the cellulose as it does have some advantages that I believe are worthwhile.

[Bob F]

I've never seen it applied wet.

Bob

[Bob F]

I just bought unfaced batts and put them in myself. It only took an afternoon.

Bob

[nospam.home]

Well I've been thinking about that too, but at my local HD, the cost of the batt is about $0.94 per sq ft, that's about $1400 for my

1400sqft home. Plus that's a lot of material to haul. I calculated 30 bags. Do you have a truck? :)

Raymond

[trader4]

I'd go with fiberglass batts too. That helps address your concern about fiberglass getting into the A/C system. When it's in batts, that's less of an issue as opposed to blowing stuff around all over the place. Also, whatever you do, if you have soffit vents, make sure they don't get blocked. If you don't have baffles in place, I'd put them in before the insulation.

[trader4]

Oh, and you also said one contractor said you might have k n tube wiring? Shouldn't be, if the house is only from the 50's. But I'd figure that out first. Not sure I'd put anything on top of k n tube, because if it's there, sooner or later you'll have to address that and if you bury it in insulation, it just makes the rewire harder.

[Nexus7]

Don't worry about it, the attic is going to be a dirty place after all these years. It should always be ventilated to the outside anyway. Dirt won't affect the R-value.

It won't insulate better than if you had all new fluffy insulation to the final height, but so what, you can always blow extra. Are they going to charge you for the final height, or just the addition? It isn't practical to remove te old stuff, there's decades worth of dust that'll ve kicked up. You hhave to wear a breathing filter even in a settled attic, so this'll be a nightmare.

Is it supply or return? A supply is at positive pressure, so nothing is getting drawn in unless there are holes (not likely).

Look into what you have. As another poster has mentioned, it is a good time to upgrade wiring before you blow more insulation, if indeed it needs upgrading. If it is conduit, you can upgrade wiring from the inside of the house.

Oh, you're willing to do some work yourself! In that case, take a can of expanding foam such as Great Stuff! up there and lay a bead around electrical box openings in the ceiling. Wear a nose mask.

You should also give consideration to blowing cellulose in yourself.

1400 sq ft is about 1.5 hours of actual blowing. You'll need a couple of helpers, but you can blow as much as you want, and it is fun!

[Steve Barker]

It's applied wet in the unfinished walls. Otherwise, it would all be on the floor. And my job also included a wet application in the attic, because it then becomes what they call "stabilized" and won't blow around when I turn on that massive whole house fan. I gave it a full two weeks to dry before covering the walls.

[Steve Barker]

Knob and tube was used up into the late '50's in the rural areas.

[Esche]

I just talked to one of the gurus of accurateBuilding.com who also show up at the Leonard Loped show on WNYC every month. I told Al that I consider to put cellulose into my walls. He said don't use cellulose, because the additives can have some negative effects; especially if then not evenly distributed. The copper sulfides (Ithink for fire retardent) might corrode the nails that get in touch with the insulation and he was suspicious about the fungicides.

He recommended: * Mineral wool * Fiberglas * Perlites

I heard good things about perlites, which don't need additives and doesn't have issues with moisture, rodents, and is very fire retardent. So I am looking into that. What I heard is that you can just poor it in.

Does anybody has experience with using perlites (or vermiculites (same category of material)) for insulation?

Thanks, Wilko

[Steve Barker]

The stuff I have doesn't have copper sulfides. It uses boric acid, which is also a good pest repellant. check out

[Bob F]

If you have knob&tube wiring, you don't want to insulate the wiring. It won't meet code.

Bob

[v]

My local (non-HD) yard offers free local delivery. This is the same yard that does a huge business with all the home builders in the area so there is always a delivery going to my area in the next day or so. Or all the HDs in my region rent trucks by the hour for DIYers to haul the stuff home; I presume they do that in most/all areas?

Don't let the mere delivery throw you. You also DON'T HAVE TO BUY/DO IT ALL AT ONCE! Heck, do six bags each day (or week) if ya wanna.

Reply to NG only - this e.mail address goes to a kill file.

[v]

Don't be so anal.

You pay for the needed volume to put the needed depth over the area in question. It all goes in. So what if you eyeball whether it is level, it will still ON AVERAGE be the specified depth, and if one spot is 1/2 inch low than another spot will be a 1/2 inch high. So what.

Don't try to cut it so fine.

Reply to NG only - this e.mail address goes to a kill file.

[Just Joshin]

Very true, I think if you want R30, you should aim higher. Also, I was told it's average thing, some areas will be higher, while others might be lower.

Just what I was told....

tom @