Insulation, Radiant and Vapor Barriers - Radiant barrier versus new insulation

We are doing some research on making our home more energy efficient. Its 26 years old and the insullation is original. Obviously every salesman has their own opinions. The 'radiant barrier' guy is telling me that by bringing down the heat in the attic, it will make it much easier to cool, but the insullation guy is saying replace the old fiberglass insullation with new bats where needed and blow in cellulose to bring it up to code of R-30 or greater (We live in Houston). We are also replacing our old a/c units which run about 8-9 months a year down here. What are ya'll's opinions on the radiant barrier vs new insullation? The insullation guy says we currently are about R-9 (could it be that low?) and the radiant barrier guy says we need about 13" of cellulose in our attic, which currently has 8". It sure doesn't look that deep to me. Thanks for everybody's opinions on this. Now I'm going to the A/C forum.

Id go with both. Insulation will not help the heat from getting in your home. Only the RB will do that. The insulation will help keep the heat in. Since you don't yous much call for heat the RB would be the 1st choice to have done.

Forget that R/B when dirt gets on it the Gov. said 5 years and its done for. Get a good blow of cellulose so you have a R 30 up there. check the vents in the attic also. You need 1 sq ft for every 150sq ft of attic 1/2 IN at the over hang AND 1/2 OUT at the ridge. They have foam forms that will go at the over hang so the air can get up into the attic from there. Over the insulation.
You could go for a attic vent fan to help. Sq ft of attic X 0.07 == the CFM of the fan you need.

I forgot to mention that the radiant barrier we are looking at is the spray painted variety, not the other type. Does this make a difference? Is it as effective? Thanks!

Insulation slows down heat transfer.

When you increase the amount of insulation it is more difficult for the heat to transfer.
It doesn't matter whether you are heating or cooling, increased insulation will reduce heat transfer in either direction.

Our cold climate calls for R-50 in attics and considering your climate is at the opposite end of the thermometer this level would not be out of the question.

The RB industry has some vocal proponents but this product has a more theoretical benefit than a practical one.
In other words don't waste your money on RB.

RB in my mind is the only way to go. Most new (high) end homes in are area have no attic ventilation. This is do to them being air sealed with closed cell foam. The Foam is a RB. If you keep the heat out you will have lower cooling bills. Ed is right when he said 5 or less years on some of these products that are out their. These products are the foil products that have a surface for the dust to land on. The coatings and the foam are better because they adhere to the roof surface so their is no air space for the dust to get to the surface. RB reduces radiant heat. Insulation can not stop radiant heat.