Insulation, Radiant and Vapor Barriers - Adding Attic Insulation

My house is about 40 yrs old. The attic is unfinished and contains about 3-4 inches of loose insulation . I would like to add more insulation to this. Can I lay fiberglass bats directly over the loose insulation or do I need to remove the loose material first and then lay down the bats.

Also how important is it to have a moisture barrier? At present there is none, only loose insulation and there does not seem to be any moisture problems in the attic. It is well ventilated with a ridge vent,two louvers at each end and vented soffets along the front and back.

you can lay it on top of the loose stuff. I wouldn't add a vapor barrier.

Why not add more loose insulation?

Thanks for advice. I could lay more loose insulation but I was thinking the bats of fiberglass may be easier to put down. Is one type better than the other in terms of insulating properties?

I think its alot easier to ensure a good coverage with the loose stuff, especially if you have alot of trusses in the road.

What location are you at? In most of climates they recommend R-38 or R-49 for attics now. Thats alot more insulation in your case (assuming R= 2.2 per inch of loose fill).

insulation recommendation map (http://www1.eere.energy.gov/consumer/tips/insulation.html#map)

The more you plan on adding the more cost competetive it is to have someone blow it in. I just added 12" to 1200 sqft and it was cheaper to have them do it than I could buy the insulation.


Here is another useful reference:

http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11390

You also might want to seal the vents at the gables.They work against the ridge vent and the soffets, interrupting the air flow. Try asking in the roofing section for better info.