Insulation Question

[Benign Vanilla]

We have an attic that has 18 year old blown cellulose insulation. In many areas the insulation is compacted, and as such I assume worthless. We want to re-insulate and I am thinking of going with rolled fibreglass batting, but I have some questions.

Should I lay the insulation down over the top of the current insulation, or should I force the batting into the joist space further compressing what is there? Can I over insulate? I realize I need to keep my soffet vents open, but aside from that, is there such a thing as too much insulation? I was at a minimum considering running two layers perpendicular to each other to be sure I get good coverage. Good idea or bad?

BV.

[Slumlord]

Cellulose insulating cabability improves as density increases. If you want more insulation, use more cellulose, not fiberglass. Fiberglass, batts in particular, allow convection current to circulate through it, reducing its effectiveness.

[SQLit]

I just blow more over the setttled stuff. Cellulose looses about 1 R per year from settling. Since I break out from fiberglass and it takes more inches for the same R as cellulose and I can not find rock wool in my area at an competive cost. I used cellulose. I found an contractor that installed an R-19 over my existing R-25 for less than what I could buy the insulation for. I also had them put R-30 over the garage. Newer home, 1999, old owner had $250 for the high, mine was $154, I have lived here for just under a year.

Check you area for insulation thickness. Lots of sites have the info. More is better, but there is an optimal thickness and after that your spending money for an diminished return. The 90 idea is an good thought.

[Benign Vanilla]

For a number of reasons, including laziness, I don't want to use more blow insulation. Thanks for the response though.

BV.

[Benign Vanilla]

We have a number of reasons we don't want to use more blown insulation, so the batting is my only bet. We looked at the Depot today, and I think I may go for two layers laid perpendicular, of R19.

BV.

[TURTLE]

This is Turtle.

Putting batts over blown in insulation is a poor job fixing to happen. I would just blow in a another R-19 on top and let it go. If your going to use batts you will have to take the blown in out and fit the vapor bearier down to the attic floor and install the batts and then if you want more put more batts or blow some more in. Having a vapor bearier half way in the pile of insulation is a moisture build up mistake waiting to happen. You have the vapor sheeting and then you have all the insulation you want on it.

TURTLE

[Tom]

But, don't they make a batt with no vapor barrier. I would think they would work. I blew cellulose in my attic once and I thought it was much easier to put in than the batts that I installed in another house, before. Rented the blower for nothing with a minimum purchase of cellulose.

>

[Astro]

I'm in the process of doing exactly that. the existing batts have vapor barriers that are either totally dried and brittle and torn up or missing entirely. That's covered by about 6" of blown in fiberglass. Some places the they layed down two batts, both with vapor barriers. Overall it's a real mess.

It's been a real PITA. Rake up the blown fiberglass. Pull up the old damaged batts. Replace non-IC fixtures and seal air leaks. Fit in new batts. Put in additional cross batts w/o barrier. Total ~R40 (in theory). Fortunately it's cold out now, so spending hours in the attic in rubber coated clothing, face mask and respirator isn't TOO uncomfortable....

Having done all that, I can feel a big difference. The fixtures make a significant difference since the old ones both allowed a flow of cold air and acted as little cold radiators. The double, cross-layered batts has really tightened things up.

Were I to do it again, I'd probably go with a nice thick layer of cellulose. I'd have had all the crappy old stuff removed, sealed up the leaks, then blown in a good fresh pile. Not a project that I want to repeat soon!

[TURTLE]

This is Turtle.

they do make a Batt type insul;ation without vapor cover but you will have to special order it and the price will reflect a costly thing to vapor type.

Now if you can use blowiable Fiber glass and not ground up newspapers with Cellulose. They will tell you that the newspaper fire retardent will wear off and you have a fire hazard after 25 years. Your suppose to remove the cellulose every 25 years and replace it because it becomes burniable after this time. Use blown in Fifer glass and it is good for a life time and never becomes a fire hazard.

TURTLE

[nicksanspam]

Where did you find that advice?

Nick

[m Ransley]

Cellulose is paper , it decomposes to dirt, fiberglass does not. Cellolose is truely Crap. Blow in or use batts of fiberglass at +50 % the area code or at a R 100 max in -20f. Yes you will see a payback, quick.

[TURTLE]

This is Turtle.

If you got time on your hands you can go down to Lowes and read the installation paper work for the Cellulose insulation they sell. It says to replace it in about 25 to 30 years for the fire proofing chemical will wear off and you should replace it. It's nothing but ground up newspaper with a chemical spraied on it and will burn after the chemical wears off.

TURTLE

[Benign Vanilla]

I was not planning on using a vapor barrier, so this should not be an issue.

BV.

[Benign Vanilla]

Or go to Home Depot, and heft it off the shelf. :)

BV.

[Benign Vanilla]

Mine is just settled. I don't have a real mess. My big issue is that at one end of the attic, I have a large pile of Halloween stuff that we just put up there. (I know, I know, very lazy) I don't want to take that stuff down, so if I do cellulose I am looking at renting the machine twice. Then there is budget. I figured if I did batting, I could buy it a little at a time, and work my way down. Then next year, do the "halloween area" during halloween when the attic space is empty.

I realize the best plan would be to remove the old, and replace with new, but I don't have the energy to do that, so I want to go right over the top. I figure as long as I don't use vapor barrie, and I don't block soffet vents, I am not hurting anything, right?

BV.

[Astro]

Then again, maybe I'd go with icynene. That stuff looks pretty good. I'm looking into using if for the walls.

i've heard various concerns about using foams in walls. Anybody have personal experience doing a retrofit and blowing icynene into existing walls?

Also, I've seen some references about using it under the roof to greatly reduce heating of the attic space, but the counterpoint is that that heat has to re-radiate out the shingle side, which can lead to overheating of the shingles. I'd be interested in hearing from people with experience in this as well.

TIA.

[Astro]

[Astro]

one option may be to set up an air gap then foam/insulate over that so that there's still air-flow directly under the roof surface. For this to be effective, I'm assuming that I'd have to add soffit venting and a ridge vent. Any reason this wouldn't be a reasonable solution.

More > oh yea, my house is old and has no soffit vents so there's no

[TURTLE]

This is Turtle.

You got me there for I did not know they had in stock all the time. I just called Lowes in Alexandria , Louisiana on Mc Authur Drive and was told by the Home building supply department that they did not stock it for it was not bought very much but if i wanted it. they could order it through one of their contractor suppliers and get it for me but it would be about 2 weeks to get it and i must by enough to cover a whole house or it was not worth ordering it.

Things must be different where you live at.

TURTLE

[Benign Vanilla]

I can buy R19 or R25 with no vapor barrier. I can get it in single bundles or in pro-packs of 4-5 bundles. I think my plan will be to go with R19, and do it in two layers.

BV.