Floor squeaks between upstairs and finished downstairs.

We have a 2 story house, the lower level is a finished den with sprayed ceiling (popcorn), one half of the above area is the living room and the other half is a covered porch. Between the living room and covered porch is a french door which sits over a enclosed I-Beam. The living room floor is laminate flooring. The porch floor is made up of tongue and groove exterior plywood subfloor, tongue and groove pine boards, another layer of tongue and groove exterior plywood, the top is a layer of fiberglass mesh with about 1/8" latex concrete (no cracks in 16 years).
The squeaks are in the floor in the middle of the 8' french door which is centered in the middle of the 20' outside wall between the living room and porch. I think the living room floor joists and the deck floor joist are sistered together over the I-Beam, I don't think the builder in 1978 would have used 22' floor joists!
There is no access from below to the area where squeaking occurs. Since the ceiling is popcorn (sprayed on joint cement) it would be difficult to remove part of it to gain access. There is about 400 square feet of ceiling, patching and resurfacing would be a nightmare.
My Stepson asked about boring holes in the 1/2" space between the laminate flooring and the door sill and squirting foam in the joist cavities. I would like your opinions.

Don

The living room is a warm zone and the porch is a cold zone. If that is correct the porch floor is insulated for the room down stairs and I would expect they would have been built as two seperate floors. You will have a rim joist under the doors and the porch will have been put on with hangers or pressure blocks. How low is the beam downstairs? I ask because most times the beam would be installed at floor height and both floors would be hung off that. If the floor joists have shrunk more than the rim joist or they are lower than a beam the plywood will lift away from the joists close to the end. Which way does the laminent floor run?

Sorry for the delay getting back, been putting out other fires!
When I bought the house, the space under the upstairs porch was open, I enclosed it about 16 years ago. I put up a temp wall parallel to the outside wall, removed the original outside wall, installed a steel I-beam. I had an architect design the I-beam. In order to conserve clearance under the I-beam he suggested a 6"x6" I-beam with 1/2" steel plates through-bolted every 12" with 3/4" bolts on each side of the web. The beam span is about 18' supported on each end by 3-2"x6" setting on the concrete floor.
There is no ridge beam over the I beam, the Living room and porch floor joist are setting directly on the I- beam.
I framed and insulated 3 new outside walls and basically doubled the size of the Den. I insulated between the floor joists with 6" fiberglass.
(I am 78 years old and have a hard time remembering how I did things over the years. Now it is coming back to me as I write.)
The laminate floor runs parallel to the I-beam.

That,s good detail, I would say your memmory is good.
The plywood subfloor in the living room was nailed down without glue or screws, toe nailing was the big trick back then. The only thing I can come up with is to have a floor guy carefully remove some of the laminent to expose the subfloor, screw that down and if that won't fix it, remove some plywood to see what is moving.

I was "the guy" that installed the laminate flooring so I am the guy to remove it, which includes moving a 600# armoir and the quarter round.
I will do it because I am also the guy sitting in my recliner directly under the squeaky floor while my wife and stepson go in and out!
Time for knee pads and a big box of 3" screws.
Thanks for you assistance.

We just did a simular job and flooring guy had a suction cup like a window cup but it was made to be hammered on for those pieces that just wouldn't move. He did dammage some but there was one new box left over. Good luck.