How much blown in insallation is needed for a 1,000 sq. ft. attic?

It's not enough to insulate a roof, one must also VENTILATE a roof to achieve good energy efficiency. You may be able to use either: a) roof mounted vents (solar or electrical activated), b) air baffles (to create a cold air space between the insulation and the bottom of the roof rafters (on a sloped roof w/ insulation in the rafter bays), or c) end or gable vents to properly ventilate your roof. Also, your blown in insulation should be able to address moisture issues, or you may need to also provide a vapor barrier (closest to the interior living side below) of the ceiling.

See the DOE's guidelines for installing vapor barriers for cold climates in the links below. (Note: insulation practices for hot, humid climates is different than cold climates. ) The Dept of energy has a pretty thorough guide to how much Insulation should be used-- based on your location/zipcode.

ornl.gov/sci/roofs+walls/insulation/ins_... However, manfs of blown in insulation will list (on the side of the bag) how many bags you will need to achieve various R insulation ratings. This R- value will vary a bit by manf. Loews Hardware website has a calculator you can use to ESTIMATE the amount of blown in insulation needed.

lowes.com/lowes/lkn?action=calcBlownInsu... Example, for a Attic that is approximately 22.5 FT X 44.5 FT (1001 SF), for a R30 value, you need about 9.2 inches deep (1022 inches) of blown in insulation, (or about R3.2 per inch of insulation thickness). But this per inch R value will vary somewhat by insulation manufacturer. For the same size attic and a R38 insulated space, you need about 12.7 inches deep (1296 inches).

About R3.0 per inch Owens Corning Insulation has a nice info sheet on how to insulate your home. The diagrams and info is easy to understand. Their recommended insulation numbers, however, are conservative (to sell you more insulation), but it is a good guide just the same.

The illustrations & instructions are very good. http://insulation.owenscorning.com/homeowners/easy-weekend-projects/weekend-project-attic3.aspx http://insulation.owenscorning.com/WorkArea/showcontent.aspx?id=888 ** ALSO NOTE: THE AMOUNT OF INSULATION IS LIKELY REGULATED BY YOUR LOCAL BUILDING CODE (i. E they actually set a minimum amount.) Most cold climate jurisdictions will require AT LEAST R38 FOR ATTICS (flat ceilings with unoccupied attic space).

Although the minimum R value could be more/higher or lower in some areas of the USA. Not complying with your local building code is considered a building code violation (i.e. Illegal).

You must also comply with vapor barrier and ventilation building code requirements as well. *** See the Dept of Energy Guides to properly insulating & VENTING roofs for cold climates. Read the Dept of Energy's Guide to Roof Insulation & Ventilation for Cold Climates (It's different for hot, humid climates) - http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/26450.pdf - Building in Cold Climates - Dept of Energy http://www.eere.energy.gov/buildings/publications/pdfs/building_america/38309.pdf Don't make the mistake of thinking venting (of your roof) is not necessary.

See the Mahalo Question on Icicles forming on roofs (and ice damming): http://www.mahalo.com/answers/maintenance-and-repairs/why-do-icicles-form-on-the-gutters-of-a-house-and-what-can-be-done-to-prevent-them-from-forming Hope that helps!

I just finished my attic and I did a considerable amount of research on insulation recently. There are several factors that influence the amount of insulation you should put down, mainly your location. But I will try to give you a simplified rundown that might help.

I live in Virginia, and to be most efficient here the government recommends a R Value of at least R-30 to R-38. If you live North of VA then the R-Values recommended will be like R-45, if you live in the South you may need less. Now I did some Quick Calculations here that will be just a rough estimate that will hopefully give you a quick idea of what you need.At my local Hardware store Home Depo they have blown in "Green Fiber" "Natural Insulation" for roughly $10 per (40sq ft, R-3.7 per inch) bag.

They base the R-Value of this bag on how deep you apply it. So if you do the math, with the Coverage Chart Fact Sheet PDF (provided on their website See Below) You could achieve: R-30 with 46 Bags (1bag 21.7sqft of R-30 Coverage) This would be 8.5 inches thick. R-38 with 60 bags (1bag 16.6 sqft of R-38 Coverage) And this would be 10.5 inches thick.

Let me know if this helps. Ohh and don't forget a vapor barrier. -MB.

There is additional information needed to answer this question. Where are you located? The amount of insulation needed will be affected by the climate in your location.

What level of insulation (R value) are you trying to achieve? Do you have any existing insulation? The R Factor of blown in insulation is 2.3 - 2.8 per inch.So if you know, how much you have, and what you need, you can do a rough estimate of ho much additional insulation you'll need to add.

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