Adding Fiberglass over blown-in

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Old 12-22-02, 03:27 PM
southtexas
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Adding Fiberglass over blown-in

Currently, I have blown in insulation in my attic with no vapor barrier. I want to add fiberglass insulation with a vapor barrier. Do I need to remove the blown-in insulation or can I install the fiberglass insulation over the top? I live in a very high humidity area, South Texas. The insulation that is in there is not very effective. In the summer, you can feel the heat radiating through the ceiling.
 
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Old 12-30-02, 11:16 PM
T
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insulation

Southtexas,

I live in Houston, and had the same problem.

Blown in should do as well as batt type, providing its deep enough. I think we need at least 9" or more here in Texas.

Batt can be laid over the blown in, but its easier and cheaper to just add more blown in over the old. Its really tough to get the batts back toward the soffet areas.

If you do use batts over the blown in, I was told to lay them across the rafters.

Forget about trying to remove the old blown in, its too nasty, and you dont have a trash can big enough for disposal.

JT
 
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Old 12-31-02, 01:44 PM
Voltswagen
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Hi,
I noticed your post about attic insulation. Have you heard about radiant barriers? You might want to look into it, it may be an effective way to keep the attic cool by reflecting radiant heat before it gets into the attic space. There are several ways to install it, one way is to staple it to the bottom of the roof trusses from inside the attic space. If you are interested, the best starting place for this is the U.S Dept. of Energy, there is good info. there as well as links to manufacturers. I can send you the URL for that website if you like. I think that in a climate like yours, a radiant barrier would make a big difference.
 
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Old 01-01-03, 10:56 PM
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Adding insulation

In unfinished attics, the roof is not insulated. The purpose of the insulation is to keep the heat in the area downstairs where you want it. You can roll out unfaced insulation over the existing insulation you have. You will need to calculate the necessary R-value.

Go http://www.doityourself.com/insulate/ on this website to learn more about insulation and to calculate your R-value for your ZIP.
 
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Old 01-03-03, 03:06 PM
rbisys
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Greetings,

Adding more FG will not improve the problem. The heat energy will still radiate thru the FG. Keep in mind that FG is about 98% airspaces. You can install a 2 layer radiant barrier(RB) insulation over the top of the existing and get much better results. The RB reflects about 95% of the heat. Humidity does not affect it.

Ck koolcoat.com (866 290 1010) about insulkating paint additive. Combined with the roof RB you can reduce your a/c considerably.

Thank you for considering my opinion.
 
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Old 01-03-03, 05:27 PM
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Been there dome that. If you dont have any vapor barrier in there now You have to put some in thats for sure .Before you add more insulation. Ill bet right now if you put your hand down in the insulation that you have now ,down low it will feel damp. This is what kills the insulation that you have now.So its a bad job but if you want it to work dig out what you have now and put in bats with the vapor side down,then put what you dug out over it.We use a 2 mil poly then the drywall. In the wall when we are done we have about an R20 + and in the ceiling with a 12" blow about an R40. Dont forget the vapor barrier on the room side not on top of other insulation. Then vent the heck out of the whole attic most of the homes I see today dont have enought vents in them ED
 
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Old 01-03-03, 06:41 PM
rbisys
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Greetings,

Installing a VB in the ceiling does not prevent condensation. In fact it can cause condensation to "pool". You lose up to 50% or more of the insulation value due to condensation. If the insulation cannot get moisture from the inside it will get it from the outside air.

By installing a RB over the existing FG you raise the temp of the FG reducing the possibility of condensation. And, again adding more FG to FG probably will not result in any meaning full savings.

Thank you for considering my opinion.
 
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Old 01-04-03, 12:32 PM
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Sorry about it but i have to go the other way about a VB.
If you like I can show you some homes that dont have a vb on the ceiling. The 5/8" dry wall on the ceiling cups down from the moisture that got there from the inside of the home ,not the out side. That would be like saying the ice forms on the outside of a window in a home. lived in one home no VB come about janurary the fuel bill would go up. You could feel the moisture in the insulation.Had to start doing our own insulation because we had to back the fuel cost on the units we put in . The guys doing the insulation would open the air shutter and give the people a good like 10" deep blow but take back about a 1/3 of the bags that should have went into the job. So you see they didnt get the R - that they should have. Have a home went through 4-01 to 4-02 tot. fuel bill $1715.34 4500' squar 3 kids 2 hotwater heaters, Heatpump ,water pumps ,lots of outside lights. With a 2 mil poly on all wall and ceiling and a house wrap. walls R20 ceiling R40. the Kw .0668 and thats by you in MO. under UE at lake of the ozarks ED
 
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Old 01-10-03, 12:01 PM
rbisys
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Greetings,

The problem is, with FG you will always get condensation and you have to try to control it. With RB you don't have the conditions to cause condensation. There are two major factors involved here. 1st it takes about 1100 btus to convert vapor to 1 # of moisture. 2nd the energy flow increases about 5% for every 1% moisture. It is a no win situation.

If you can locate a % eff. per "R" value chart (good luck) you'll see that going from a "R" 19 to "R" 36 only increases the eff about 7.5%. Taking into consideration that only about 20% of the heat goes thru the ceiling and that the increased masss will store more heat for later release into the home(summer) means that it's a waste of money. Remember FG is about 95%+ air spaces and the glass itself is less than 10% efficient against heat energy. The pay back on 6" FG walls is about never. The very fact that you have to use such large amounts and still get the excessive fuel bills you mentioned should raise a red flag.

I'm glad you brought up the problem of installers shorting the builders and home owners so they have free material to make money on the side. BIG PROBLEM. I've had many builders say they don't care as long as a have a receit stating that the ordered amount was blown in.

The above is why I prefer RB insulation. Will out perform any amount of FG and cellulose you can put in a home and you don't have moisture problems. Lasts fo the life of the building.

You mention RB to UE and see what they say. They have killed alot of RB sales.


Thank you for considering my opinion.
 
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Old 01-10-03, 02:09 PM
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Now why do you think UE killed all the sales of your RB ????????
As far as excessive fuel bills,man where do you come from.
With 2 adults 3 kids 4500sq' home 2 hot water heaters 3 fridges lots of out side lights, water pumps, dock lifts,heat pumps, a/c, and all the cooking for $1715.34 .You better take a look at your bills for the year.
Also I like cellulose insulation over FB because in a fire the FB will not burn but it will melt and let the fire get down into the home. Have some pictures of homes that got on fire up in the roof.You know that is all that burnt the roof.It didnt get the rest of the home because of the cellulose insulation. Can your RB do that? Also we find the 6" walls or out no good. lets see the bills on a home with your RB on all elec. heat and A/C for the same sq ft ED
 
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Old 01-10-03, 04:44 PM
rbisys
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Greetings,

Good for FG maybe.

Fire will not come thru ceil'g under conditions you mentioned and probably not thru wall either. RB does not burn and refects heat of fire back to source. Even if it does fail, eventually, it can give you more time. One reason cellulose does not burn, besides the chemicals, is that the chemicals cause the paper to hold more moisture. This moistuire is released in a fire. Cellulose can hold up to 50%+ moisture compared to FG. NBS released report in 70's showing that FG held about 9.5 % moisture and cellulose 14%. Using the 5% to 1% ratio you get about 48% increase heat flow for FG and 72% for cellulose. You don't have this problem with RB.

How can you say that RB will not perform better than RB if you have never done a RB house?

Chemicals leach out of cellulose. I know, I've checked older cellulose. RB out performs cellulose too.

Thank you for considering my opinion.
 
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Old 01-11-03, 12:13 PM
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Like I said show me some bills for elec heat and AC on a home with RB ED
 
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