Insulation Question

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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.
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Benign Vanilla wrote:

want more insulation, use more cellulose, not fiberglass. Fiberglass, batts in particular, allow convection current to circulate through it, reducing its effectiveness.
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For a number of reasons, including laziness, I don't want to use more blow insulation. Thanks for the response though.
BV.
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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.
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<snip>

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.
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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
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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.

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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.
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Where did you find that advice?
Nick
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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.
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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.
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Come now. Do you really believe a company could sell insulation with that restriction? :-)

I did that, and spoke with a Lowe's employee, and looked at their celluose insulation web site:
http://www.greenstone.com/firesafety.asp?Type

I'm afraid not. Here's a quote:
U.S. GreenFiber - Product Specifications - Fact Sheet - Fire Safety Cocoon insulation enhances fire resistance and is guaranteed to retain its fire retardant characteristics for the life of the structure. Cocoon is treated with fire retardants, has a Class 1 fire rating and is nonflammable when tested for smoldering combustion.
Alternative to Fire Blocking
Cocoon can also be used as an alternative to traditional building code fire blocking measures. Fire rated walls filled with Cocoon will meet building code provisions for adequate protection around non-combustible through penetrations. The ICC Evaluation Report #2833, section 2.5 Fire Blocking, states Cocoon insulations are permitted as fire blocking under Section 708.2.1, item 1 of the UBC and are permitted to be used as alternates to the fire blocking in Section 602.7.1, item 1 of the CABO One and Two Family Dwelling Code.
Normally, membrane penetrations for such things as wall receptacles require a separation of at least 24 on opposite sides of a fire rated wall. However, if the wall is filled with Cocoon insulation, the horizontal separation need only be equal to the walls thickness.
Outperforms Other Materials
THE BIG BURN, a home fire demonstration, was performed in 1998 at the Maryland Fire and Rescue Institute under the supervision of both The Code Consortium, Inc. and Steven Winter Associates. The results of this demonstration correspond closely with the results achieved by the National Fire Laboratory of the National Research Council Canada. The cellulose structure maintained its structural integrity, for a total time of 68:08 minutes, in excess of 24 minutes longer than the fiberglass structure, translating to an increased fire resistance of 57% as compared to the 55% improvement achieved in the laboratory study.
Surface Burning Characteristics
Cocoon has a flame-spread index rating of 10 and a smoke developed index of 0, exceeding the standard flame-spread index of not more than 25 and a smoke-developed index of not more than 50 as tested in accordance with ASTM E 84. Cocoon meets the ASTM C 739 requirement for Smoldering Combustion and Critical Radiant Flux. UL has classified the U370 wall for a 2-hour fire resistance rating according to ASTM E119.
GreenFiber has UL approval for the use of Cocoon insulation for many construction designs listed in their Fire Resistance Directory.
U.S. GreenFiber, LLC 809 West Hill Street Ste A |Charlotte, NC 28208-9924 Phone: 888-592-7684 | Fax: 704-379-0685 Email: snipped-for-privacy@us-gf.com

How does the chemical "wear off" inside an attic or wall? :-)
The Lowe's web site also recommends very tight house air sealing, with links to DOE web sites...
Nick
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<snip>

Or go to Home Depot, and heft it off the shelf. :)
BV.
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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.
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<snip>

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.
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This is Turtle.
Watch going over R-40 because of you will start to store heat after it cools off or warms up outside.
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Well... yes, but that's what windows are for.
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This is Turtle.
You might have left out one thing here. Here is Louisiana we may run the heat in the morning to get a chill out of the house but sometimes it will go to 80F to 90F by mid-day. When you have to go from heat to cool and a temperature change like this. You will store up heat in the insulation to still be coming into the house 3 to 8 hours later. You can get in contact with insulation manufactors and they will tell you about the over insulation point of their business. So there is a point where you can over insulate a house to cause a cost problem to take care of stored up heat.
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<snip>

I wish that was a problem up here, but it's not. Sounds like a good problem to have.
BV.
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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!

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