I recently install radiant barrier in my attic and will be adding insulation (I'm down to about r-13 or so) to R-38 or so. Would it be beneficial to blow in insulation between the radiant barrier and the roof decking? I figure the worst that could happen is the weight of the insulation tears the staples holding the barrier and falls on top of the additional insulation. I've used a ton of staples in hopes this doesn't happen, but who knows. I plan on blowing the white fiberglass insulation due to it being lighter than Cellulose. I've checked with my Utility company Energy Efficiency dept and he's never heard of anyone doing this. What are your thoughts?

There are worse things that can happen, somewhat climate dependent, but not entirely. By installing insulation between the RB & roof deck the roof deck is colder in winter, and accumulates more moisture over a winter, raising the rot risk. If the radiant barrier isn't a perforated "breathable" type insulation that slows the air flow in the channel between RB & deck slows the drying rate of the roof deck as well.

But for the record, where are you located, what it the radiant barrier type, and what attic ventilation scheme (if any) does this house have.

Only have gable vents on either end of the house. According to the mfg of the RB... "(ASTM) Class 1 Class A fire and smoke safety requirements of most state and local building codes, as well as the breathability standards for building materials."

Some aluminized-fabric radiant barriers have tiny perforations on a ~1/4" grid, which allows moisture to pass from one side to the other. Most RB is smooth, and a true vapor barrier with the potential for trapping moisture. (The risk is lower with perforated RB.)

Climate still matters. Location of your house is...? (I'm assuming it's not in Fairbanks, AK. :-) )

LOL, no not Alaska. I'm in Central Texas....close to Austin. I just looked at the RB and there are a ton of small pin holes in it.

You're pretty safe blowing cellulose behind perforated RB for a vented attic in Austin, but the benefits will be pretty small if you already have R38 on the floor. The benefit would likely be higher adding that cellulose to the R38 on the attic floor. Having the RB in contact with the cellulose reduces it's effectiveness slightly, but not enough to matter. But the attic venting thermally bypasses any insulation at the roof deck (unless you seal the attic.)

FWIW: Even though it's not very risky as long as the RB is perforated and the attic is vented, putting the insulation against the roof deck as-described would also technically be a code violation, unless you had at least R5 of insulation (say, 3/4" of polyiso foam board) above the roof deck.

So, did you have to wear fishing waders to take a walk in the neighborhood this week? :-( I know it was nowhere near as bad in Austin as closer to the coast, but heavy enough. I was almost expecting an old guy with a huge boat full of mating pairs to be featured on the evening news...

Thanks for the advise. Since it will be a pain to do and with little benefit, I'll just add a little more to the flooring. We didn't have it bad here, 10" of rain, Houston and the coastal towns are a different story. It will be years before they are back to where they were.