R8 in an attic is part of the energy code & I don't know how Florida works but I'd be surprised if they hadn't adopted that code.
As for how much difference, my guess would be around 15% more duct loss which is not a whole lot compared to the total btu loss of the structure.
It's still enough that it pays to go with R8 in the long term.

 

If I'm reading the code correctly, Florida requires a minimum of R8 for all ducts larger than 3" diameter that are installed in an attic.

 

Would you consider R-6 or for that mater R-8 sufficient insulation value for your attic? Insulation doesn't cost that much compared to a lifetime of energy costs due to heat gain or heat loss through ductwork.

 

You get to pay for the difference every hour the unit runs or get the savings.

 

Any contractor that uses r6 in a Florida attic should be relieved of their services


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Why?

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That is the energy conservation code? What building code cycle is Florida on? Check 403.3.1 of the building code perhaps?
At the end of the day, it doesn’t matter to me.. just sayin


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Hmmm


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wouldn't all that insulation on top of flex duct compress it?

 

It may compress the duct insulation, but the benefits of insulation cover in the attic far outweigh the slight duct compression.

Attic space is the WORST place for ductwork in the south.

 

would you say that R6 plus the 8 inches over top insulation is good and R8 plus insulation would be overkill?

 

__ NO ONE said it would be Easy to significantly increase the effective R-value.

The overall background & INSTALLATION CRITERIA
for DUCTS WITHIN THE CEILING INSULATION

https://basc.pnnl.gov/resource-guides/ducts-buried-attic-insulation

https://basc.pnnl.gov/code-complian...nce/buried-ducts-within-ceiling-insulation-vented-attics-all-climate-zones-code
_
Decreasing the equipment size is VERY IMPORTANT.!

 

It appears I stand corrected. From what I gather, Florida is in 2017 and it says r6.

Very interesting to me (as a New Yorker) that the code is less stringent in Florida than NY. It is just a sore subject to me in that we are required to have R8 and of course trying to do things properly cost more money and losing jobs to chuck in a truck hacking in less cost non code compliant products gets very tiring.
After doing some research a couple years ago, I was shocked at how much difference it made going from 6-8 (as Dan pointed out also)


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No, I'm trying to decide whether to go with R8 over R6 flex duct, vs. just insulate over R6. I can't afford hard duct, unfortunately.

 

Whats there now?

 

Seems if you did the latter it would be more expensive however you would end up with a higher overall ceiling R unless you can buy R2 insulation rolls.
Doubtful
You can get R2 in a 4x8 panal but as you know that's not going to work for what you're trying to do.