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Yoyizit 10-22-2008 01:34 PM

blown in attic insulation, replace or add to
Anyone know the service lifetime of this?

joasis 10-22-2008 01:37 PM

Forever. You can add to it and there is no reason to remove the existing.

Cellulose will "settle" over time to a degree...but it's insulation value does not decrease as much as some believe. It gets tighter as it settles. 12 inches of cellulose weighs about 1 pound per square foot, so the weight isn't really an issue either. My son, who does this for a living, has been getting a lot of calls to increase the insulation to 16 inches and a few for 2 feet.

KE2KB 10-22-2008 04:43 PM

I have Rockwool in my attic and walls. Never known there to be a "life" on the stuff. Seems like it'll last forever!
Is cellulose the same thing as Rockwool?
I like the stuff when I'm doing wiring. It doesn't cause me to itch later the way fiberglass does.

Yoyizit 10-22-2008 05:01 PM

Should I then shovel it up, replace the vapor barrier, and then reapply the same stuff and add some new? Right now it's at 3-1/2" deep.
This stuff is from 1964.

joasis 10-22-2008 07:10 PM

I doubt you have cellulose if it is original. Cellulose is 100% recycled newsprint, paper products, and bags and boxes, treated with boric acid for fire and insect resistance...and I doubt anything like that was done in '64. I bet you have rockwool.

Termite 10-22-2008 07:14 PM

And no, shoveling it up and getting rid of it is just unncessary. Insulate right over the top of it, and continue to benefit from what's there already. You can use basic cellulose over it...No need to stick with rock wool.

Yoyizit 10-22-2008 09:00 PM

If the paper vapor barrier is ratty, don't I need a new one?

joasis 10-23-2008 07:00 AM

No, cellulose as it is made today is toxic to insects and rodents. The advantages to a ceiling vapor barrier are questionable, and in your case, not needed.

dac122 10-23-2008 08:12 AM


Originally Posted by thekctermite (Post 175507)
And no, shoveling it up and getting rid of it is just unncessary. Insulate right over the top of it, and continue to benefit from what's there already. You can use basic cellulose over it...No need to stick with rock wool.


KE2KB 10-23-2008 09:13 AM

Old newspaper?
While doing some wiring in my closet, I found the rockwool insulation, and some very old newsprint. Some of it was actually readable, pre-ww2 stuff.
I scanned whatever I could into my computer. The paper disintegrated almost as I touched it though.
Nothing of value, just interesting what you find in an 80 yr old house when you start to rip open walls<g>

Winchester 10-23-2008 09:41 AM

Add the cellulose. Did this myself just this past weekend adding to the existing blown fiberglass. Approximately 18"-19" total now or and estimated 50+ R-value!

Yoyizit 10-23-2008 10:59 AM

This stuff doesn't burn. It sort of chars.

Thanks for all your answers!

Yoyizit 10-30-2008 04:09 PM

Turns out for $250 mat'ls cost I can add 3-1/2" unfaced fiberglass to the existing stuff from an insulation place in MD. Cheaper than at Home Depot, if they had what I wanted.
This will probably pay for itself in one season here in the DC area.

Turns out that the multiple layers of ceiling paint of the floor below in this 40 yr old house acts as a vapor barrier, so I leave the old stuff and the kraft paper undisturbed. No dust, no fuss.

Using a thermistor, I made surface and air temp measurements on both sides of the ceiling with the existing setup, so I should be able to figure out what improvement I get, based on degree days for this area.

One of my customers with a similar size house paid two kilobucks for a layer twice as deep, blown in. Twice as deep as needed for our area, according to one chart I saw.
I also read that some stuff blown in is so dense it can collapse drywall. Not so with fiberglass.

So I figure I'll be paying myself about 400 tax free dollars per hour. For that I'll be glad to scramble around in an attic and scratch my head on the roofing nails sticking through. Oh, yeah!

Thanks all. . .:thumbsup:

joasis 10-31-2008 07:31 PM

Placing unfaced fiberglass is going to be a total waste of your time and money. Sorry to break it to you, but that is the way it is. Go and buy the bags of cellulose and they will loan you the machine to blow it with in most cases.

Another thing, I don't know where you get a "chart" that shows demographically what is the "needed" value is....usually, the building code guy can tell you what code is, but you will not be able to "over-insulate"....

beenthere 11-01-2008 05:48 AM

That chart may just be showing you the recomended minimum for your area.

Adding insulation to the attic is almost always a good idea.

However. Most people overlook infiltration.
Seal your windows, outside wall switches and receps, replace worn door seals. It will pay you back fast.

It will help to keep the humidity up in your house, so its a big comfort improvement.

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