Are you referring to radiant barrier? Some are foil faced with a kraft paper backing and fiberous mesh inbetween, others are foil faced both sides, and some are perforated while others aren't.

Radient barriers work well, but roofing materials have to be suitable for their use. The barriers make the roof a lot hotter and can degrade asphalt shingles much more quickly.

Hi Handy, That's true when using techshield plywood as sheathing, but installed properly on the underside of the rafters with a continous run ridgeventing/soffitventing allows the heated air to escape on out the ridge. The radiant barrier traps the heated air between the roof sheathing and the space below the rafters,( in the rafter cavatie). As long as their is an avenue of escape for the heated air, it wont effect the shingles. I believe what the o.p. is referring to as far as installation, is laying the radiant down horizontally over the insulation/joists, which is another install method. Some radiant barrier outfits will tell you the latter install method is ineffective due to dusts building up on the product, while others state that dusts have no effect whatsoever.

Correct, the barrier would be placed horizontally on top of the ceiling joists and above the existing batt insulation.

The ultimate question is whether it makes sense to pay $2400 for the radiant barrier or spend the same amount or less on more typical (blown in) insulation? The attic is approx 1300 sqft.

What would give the most bang for the buck?

Thanks for the feedback.

Are you fairly handy as this is a pretty straight forward install concerning radiant barrier or blown in cellulose. With blown in, many places will let you use the blower if you buy the cellulose from them, or you can rent the blower. The radiant barrier typically comes in 50" width rolls where you overlap 2" for a 16" on center layout. The amount of rolls dependent on sq.footage of the project. You could save the labor doing either project d.i.y. as long as you still qualify for the tax rebate going this route.

radiant barriers raise temps 2 to 3 degrees not enough to
shorten shingle life or void warrenty.

the correct install is to install rb on the undersides of
roof rafters with foil facing into attic space.

when laid on attic flooring the reflectivity is reduced by dust buildup and within a very few years becomes useless.

by placing the foil on the attic floor you are allowing
the radiant gain into the attic that installing the rb on
the roofline reduces.

there is no 30% savings..
not even in my my hot climate..
while there is a benefit it is only for hot months as rb's have little to no savings for heating climates/seasons.

visit www.buildingscience.com and search for radiant barrier info
florida solar energy center has diy info and is also
an unbiased (read..selling no products) source..

I diy'd my radiant barrier..about 9 hours to do
4 on 12 roof pitch over 900+ sq ft. single sided
foil faced kraft paper installed with button cap nails.

best of luck.

This is actually for my parents in Iowa. Primary reason is to reduce heating bills. Sounds like the double sided perferated aluminum foil helps mainly in summer months, but may not help as much keeping the house warm during winter?

http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm#payback

there are better efficiency upgrades for your parent's location. this isn't one of them. these rb pkgs are often sold to older people who buy into the ease of saving
30%..read the article for specifics.below are
a few excerpts..

from the link:
Attic radiant barriers made of aluminum foil are becoming a popular way for homeowners to save energy and money in SOUTHERN states.

Can't I just roll the material out on top of the insulation?
Placing the material directly on top of insulation is not recommended. In this type of installation, dust will accumulate on the foil surface facing the roof. In time, the dust will negate the radiant barrier effect.

Will heat build up in the roof and damage my shingles?
It's extremely unlikely. The Florida Solar Energy Center has measured the temperatures of roof shingles above attic radiant barriers on hot, sunny summer days. Depending on the color of the shingles, their peak temperatures are only 2-5° F higher than the temperature of shingles under the same conditions without a radiant barrier.

best of luck