The dining area of my kitchen is built over a crawl space that's enclosed by
cinder blocks like the rest of the house. In the basement, there are two
openings to this crawl space, but they're only 6" high x 18" wide. I assume
they were put there for ventilation purposes, since they're useless for
anything else. The area in question juts out from the main kitchen, and is
12x12 feet.

In winter, the floor is ice cold, so that dining area is useless. I believe
the traditional first step for dealing with this is to lay a plastic vapor
barrier on the soil underneath, followed by fiberglass insulation. The vinyl
flooring needs replacement, so I could also rip up the wood underneath in
that area and have total access to do the work. Replace the sub-floor
afterward, install new vinyl or tile, and it's done.

BUT: Someone suggested an interesting alternative: When the vinyl flooring
is removed, drill access holes in the sub-floor and pump the space full of
foam. It's already a form of plastic, so it should form its own vapor
barrier. And, it'll insulate. Progress could be checked via the access slots
in the basement. Makes sense, but there's always a "gotcha".

Your thoughts, please.