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Attic insulation: lay it perpendicular or in the same direction?

Attic insulation: lay it perpendicular or in the same direction?

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  #1  
Old 02-11-03, 10:37 AM
gubs18
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Attic insulation: lay it perpendicular or in the same direction?

Simple question: I have a 30 yr old home that has 3.5" of existing FG, leaving a gap of .5 to 1.5" below the truses (which are 2x4).

If I were to add more FG, would I lay the new FG perpendicular to the existing, or in the same direction as the existing?

While probably doing both may be best, what would be best if I only did it in one direction?

Thank you!
 
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  #2  
Old 02-12-03, 09:09 PM
R
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While batt insulation is relatively inexpensive and easily obtainable, when it comes to adding more insulation to figerglass batt insulation, the best type is loose fill fiberglass insulation. It is less expensive than batt type and easier to install and on top of that, it almost assures 100% coverage.

You could search the web for suppliers or go to your tool rental store and they will probably sell it. If for some reason you cannot find it or you prefer to use batts, then I would recommend that you either install the batts paralell or perpendicular provided there is no spaces or gaps between the two layers of insulation.
 
  #3  
Old 02-13-03, 06:40 AM
Brewbeer
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I'm also for blown-in in your situation. Gonna be hard to lay bats arround the trusses (do you have trusses or joists and rafters?).

Contact your electric company, and if you heat with gas, your gas company, to see if they are offering any incentive programs. The utilities in my area will pay 1/3 the cost of upgrading energy saving features, including adding insulation to the attic and walls of your house.
 
  #4  
Old 02-13-03, 07:09 AM
gubs18
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thank you...

I would use cellulose (or RB), but I think I need the advantage FG affords, since it can easily be moved out of the way so I can:

1) do future home improvements, like run wiring for future ceiling fans in the rooms below
2)install whole house fan in hallway ceiling (so Iím not sure if the little cell pcs would blow around my low hip roof(?)).
3) store light items up there in the future, on a platform with FG underneath (since I have no basement)

the idea of having to move cellulose's little pieces, in order to work in an area or to move about the attic, seems to be easier to use FG (I just flip the batts up & out of the way).

Waiting on Rbisys for RB info.

Thank you Resercon for your info... Home Depot tried to tell me the gap "was good to have, like a dead air space", but I thought I read on these boards that you don't want a gap)....thanks for confirming...

Do you have an opinion/facts on RB in attic?
 
  #5  
Old 02-13-03, 09:29 AM
R
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RADIANT BARRIERS

They have been around for some time and was probably the first type of insulation people applied to dwellings. Radiant heat transfer is how heat from one object transfers heat to another object through waves, very much like the sun radiates heat to the earth. The principle applies to any object that is warm can radiate heat to its surroundings and other objects. Also degree temperature difference, including how hot an object is determines the rate in which heat is transferred through radiation.

The three types of heat transfer are Radiant, Convection and Conduction. All 3 are present when heat is transferred. For example, in the summer the dominant heat transfer mechanism is radiant. The reason for this is degree difference of the roof verses the home temperature. Let's say the roof is 165 degrees and the inside home temperature is 75 degrees. The difference is 90 degrees. Radiant barriers prohibit this degree difference from affecting the temperature inside the home by reflection. Conduction and Convection heat transfer are present during this heat transfer, but play a smaller role in maintaining the inside temperature because the warmer an object gets, the more heat that object will radiate. This does not mean that heat transfer by diffusion and capillary action (Conduction) and/or Convection (air leakage) should be ignored or doesn't play an important part in preventing heat transfer during the summer. What it does mean that there is a greater pecentage of heat transfer with radiate than the other two.

In the winter the dominant heat transfer mechanism is diffusion which is Conduction. The reason for this is surface area. This is the area of the home that physically separates the outside from the inside temperature, including floors that are either a slab, crawl space, above garage and/or basement. Plus all exterior walls and the attic floor. Unlike during the summer, the attic dominates the heat transfer, in the winter there is no one section of the home that dominates. Hence the use of insulation in homes because it addresses Conductive heat transfer by restricting diffusion. Radiant and Convective heat transfer maybe present, but pales in comparison to Conductive heat transfer in the winter.

Another consideration is that high pressure areas are attracted to low pressure areas and that high pressure may have an affect on temperature but has no affect on radiant heat transfer. What that means is the pressure induces diffusion and that aids the heat transfer in the attic during the summer. If you couple that with reducing roof temperature with the installation of a light colored roofing shingle and attic forced ventilation, the controversy over radiant barrier has merit.

Even though I may understand the principles of radiant barriers and its benefits, I use it very infrequently. Then again, I do live in the Northeast, pehaps it would not be so if I lived in an area where the climate was warmer.
 
  #6  
Old 02-18-03, 02:11 PM
rbisys
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Greetings,

They use RB in the Arttic, space ships, Minn. and there was alot of RB installed in the 50's in NE government jobs.

Unfortunately the government has tried to discourage use of RB by publishing misleading info about RB. If you notice they do not tell you under what conditions they are testing. They also do not tell you that the RB will out perform the FG under any conditions I'm aware of. You can use them in any climate you want and they will definitley out perform FG without any of the serious FG problems. Also they do not lose "R" ( up tp 50% for FG), they maintain it for the life of the building.

Thank you for considering my opinion.
 
  #7  
Old 02-18-03, 05:45 PM
gubs18
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Rbisys,
When you have a chance, pls send me your samples & instructions you claim are much better than FG (I have written to you a number of times & haven't gotten an answer). Thank you ..... look forward to seeing them.....
 
  #8  
Old 02-20-03, 07:40 AM
rbisys
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Greetings,

I thought I had sent material to you.

If you e-mail me your address I'll send the latest I have.
[email protected]

Thanks for your continued intrest.
 
  #9  
Old 02-20-03, 10:55 AM
gubs18
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Thank you.... I have sent you my address in a private msg to you.

Look forward to the information.
 
  #10  
Old 02-21-03, 04:33 PM
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insulation

Try this www. and see just what the US government thinks about the R B. They say with FG you do get a pay back over the RB.

http://www.ornl.gov/roofs+walls/radiant/rb_02html ED
 
  #11  
Old 02-21-03, 10:19 PM
lou s.
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Resercon,very nice report there.I think that was an excellent coverage. Gubs,I too would recommend loose fill fiberglass,over rolling out the batts-it's a royal pain,and loose fill does a much better job.Cellulose is also very effective,but it gets EVERYWHERE,and man o' man does it taste BAD!!.Make sure to leave some space at the eaves,so the attic will air out.I would also suggest you get up there before it gets too warm out.Been in a few attics when it's around 90 outside,but the thermometer in the attic reads around 120-140.Takes not too long to get red-faced&white eyebrowed!
 
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