My house has batt insulation and is not air sealed. I did build my own insulated cover for the attic pull down stair. It has a tight seal around the perimeter. That is relatively easy to do with simple tools.

It is going to be very difficult to seal an attic with 12+ inches of insulation without removing it. You should not attempt to walk around an attic once the insulation is installed. This is one of the reasons I prefer batt insulation, and I am glad my attic was insulated that way.

I have read about the benefits of sealing an attic. Yet I have never seen any data of how much energy is saved. I question how much money is actually saved by sealing.

Great stuff and caulking are good products to seal any air gaps. Seal any obvious gaps that you can easily reach. You have to decide whether it is worth removing and installing new insulation to reach other places.

Since I went heat pump, I decided to attack all the air leaks I could get to.

My 1954 house had 1" (yes, one inch) paper-wrapped rock wool (I think) batts in the attic floor. I spent some time up there taking it all out. It was messy since the paper was crumbling as soon as I looked at it. I'd compare this to removing your loose fill.

After that was done, I stapled styrofoam baffles at the low end of all the rafter bays to allow for venting.

Next was sealing around all electrical boxes from the ceiling below and cable penetrations with caulk when the gap was small enough then Great Stuff if it was too large an opening. Also installed high hats covers.

Then I rolled in kraft faced fiberglass between the joists and unfaced fiberglass perpendicular.

I did see some savings energy savings over previous years doing an honest comparison. If I had to pay someone to do this project, I probably wouldn't have done it. I went back and forth between blown and fiberglass and am glad I chose fiberglass. Navigating the exposed joists was tricky. I used a bunch of different sized boards to do it. A lot of crawling on the belly too.

I also sealed the rim joists in the basement. Much easier and a big help against "stack effect".

Here's the glossy government brochure:

Energy Star Attic Air Sealing

Good luck!

what is it you hope to achieve with air sealing the attic?

are you sealing ambient air out of attic (unvented attic)?

or are you air sealing the living space from the attic space?

what is your location?

once we know these details we can better address your

questions.

as someone who has done air sealing work for a long time...

I have issues with the energy star methods. I would not

recommend using foil bubble foil, or insulation stuffed into

bags to air seal. testing these methods with blower door shows

that they fail quickly. foam board, backer rods & caulk.

unlike great stuff that fails quickly, these materials will

expand & contract & air seal will not fail in years to come.

this link I find is the most comprehensive one for air sealing.

deals with the whole house & not just attic.

http://www.southface.org/wp-content/uploads/2016/07/georgia-code-iecc-appendices-2009-1.pdf

best of luck