Years ago I worked for a utility company in PA as an energy conservation specialist. We always taught that when installing insulation anywhere in the house, the vapor barrier went toward the heated side in winter. In Florida it would be the air-conditioned side or your living space. In the attic, the vapor barrier would go against the floor which would be directly above the ceiling of your home. Insulation could be added above that. If a vapor barrier was placed on top of the insulation, it would trap moisture which would condense and wet your insulation below it, therefore reducing your R-value as well as causing moisture problems in your home. A radiant barrier is different than a vapor barrier. A radiant barrier reflects heat outward. That is placed on the roof rafters, not on top of your insulation. As to interfering with electronics, that depends on the material that the radiant barrier is made of. Not all radiant barriers are the same. They are different in their components as well as their thickness and of course like with anything, you can get an excellent product and have a lousy application. Remember too that your soffit vents should never be blocked. That is important to allow airflow from the floor of the attic up to roof vents, ridge vents or ventilation fans. Ductwork should be wrapped in insulation because most of the time it is run in unconditioned spaces: in your garage or attic where the temperatures are very hot when you are trying to air condition your home or when the temperatures are cool and you are trying to heat your home. Most utility companies have people to help educate homeowners and government or university sites online are also helpful. It’s best to get your information from a place that is not selling any product. I have always added additional insulation in homes I have lived in. In our Florida home, I researched radiant barriers and we did have them installed from garage through covered lanai. That has made our attic space cooler which is good for anything you have stored up there but primarily for keeping the house cooler since the space directly above our ceiling has dropped in temperature.

The expression is there is no free lunch. They are bribing you to attend their sales pitch.
We went to one where they wanted to manage your investments. They handed out forms which many, most people completed. How could you say no to someone who bought you lunch? Mine was BLANK.

My comment is based on your post: When you walk in the attic, it looked like an igloo, but the attic was 70 degrees all year round, and that’s with 100 degree humid days or 15 degree nights. . That is impossible without using your HVAC to condition the attic temperature unless you had your house set at temperature much lower than 70F in the summer and much higher than 70F in the winter. The attic space which is between two very different temperatures zones will gradually change to a temperature somewhere between your conditioned house space and the outside air. Insulation slows down the temperature change but can not stop it. Since the outside temperatures keep changing, the attic space will continue to change but will remain between the two temperatures for typical temperature rate changes. This is fundamental Thermodynamics.

With 10 inch foam on the roof and no insulation in the ceiling of the home, heat transfer from the home will be greater than heat transfer through the roof insulation. You also stated that the attic was sealed with no ventilation so the heat transfer is basically across the insulation and ceiling. The attic temperature will tend to be closer to house temperature than the extreme outside ambient temperatures. If your 70F comment was "~70F in winter and ~79F in summer" I could see that happening. Your inside house space is cooling the attic somewhat in summer and heating the attic somewhat in winter. Again it depends on what your house temperature is.

Nobody is talking about reducing the attic temp by passive means.
I came from Kansas where we used wind turbines on houses to draw up cooler air from soffits and exhaust hot air out of the attic. I know there are solar fans that you can replace a existing mushroom vent on the roof but they can tend to draw in air from nearby exhaust vents and just circulate air between vents instead of from soffits.
What is the recommended number of exhaust venting for a home?
My new home in St Catherine’s has only 2 mushroom and very small amount of ridge venting because of lack of ridges.
I’m just guessing that since all of the soffits are open for venting, increasing the amount of exhaust vents or adding turbines has to help reduce the attic temperature for a minimum amount on money spent.
Anybody have an answer?

Reducing attic temperature
 

Nobody is talking about reducing the attic temp by passive means.
I came from Kansas where we used wind turbines on houses to draw up cooler air from soffits and exhaust hot air out of the attic. I know there are solar fans that you can replace a existing mushroom vent on the roof but they can tend to draw in air from nearby exhaust vents and just circulate air between vents instead of from soffits.
What is the recommended number of exhaust venting for a home?
My new home in St Catherine’s has only 2 mushroom and very small amount of ridge venting because of lack of ridges.
I’m just guessing that since all of the soffits are open for venting, increasing the amount of exhaust vents or adding turbines has to help reduce the attic temperature for a minimum amount on money spent.
Anybody have an answer?

Hey hey! Throwing stones you just might hit someone :bigbow:

I don’t know what the talk about 10” of foam is all about what I saw in attics in Ga was more like 3” but a complete coating of sheathing, rafters and gable walls

See OP post #32 rsmurano:
If you are responding to my thread, no, we didn’t cool the attic. Our builder only used the spray foam that was over 10” thick on the attic roof. There are 2 kinds of this insulation: closed cell and open cell. We had friends that retrofitted their attics with the open cell spray foam at a cost of $8000 for a 2400 sq ft, and their attic in the middle of a GA summer was also 70 degrees. There is no magic to this. The other benefit to this in GA is your furnace lasts longer because they are located in the attic. A furnace running in a room at 70 degrees will last longer than a furnace running in an attic at 140 degrees

That's the source of 10 inch foam. You may have seen closed cell foam which has double the R value of open cell foam.
Over and out. This thread has passed the point of diminishing returns.