I can't think of a climate that would benefit from foundation vents but what is your climate and soil/drainage conditions.

If you seal the crawl space provision must be made to ventilate it and possibly insulate it. The requirements should be spelled out in your building code.

Vapor barrier at a minimum.

These are just based on averages, but temps reach into the mid 80s in the summer and into the low teens in the winter. Average humidity is about 46% with an average of 30" for rain.

What is the applicable building code?

I would pour a maintenance slab over a true vapor barrier, Larry the barrier up the walls, insulate the insides of the walls and introduce air from the living space above to keep it dry. If there are a lot of ducts in the crawl space air leakage might be enough but it isn't recognized by most codes.

Average humidity of 46% means basically a desert climate (Arizona, New Mexico, Nevada, etc.).

There are lots of good reference materials available on the web regarding the cost and benefits of conditioned v. unconditioned crawl spaces. Here's a good place to start:

http://energy.gov/sites/prod/files/2014/01/f6/1_1d_ba_innov_unventedconditionedcrawlspaces_011713.pdf

VENTED CRAWL SPACES ARE THE DEVIL'S SPAWN!! (Actually, I think the real reason they exist is because it's cheaper and easier for the builder; it's the lazy man's approach.)

I have an unconditioned crawl space. The HVAC and associated ductwork for the first floor live down there so every time I walk in the house, I smell crawl space. The wood and tile floors are so cold in the winter that water actually freezes if it's spilled on the floor! (It doesn't really, but, it feels like it could.)

My house was built in the early 90s using pretty standard construction techniques and materials:

• Concrete block foundation with aluminum vents
• Black plastic (not sure of exact material or thickness) covering the dirt
• Fiberglass bats between the floor joists

The guy you're really looking for is Martin Holladay over at Green Building Advisor. He knows everything there is to know about this subject (and every other related subject). http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

I have not designed a house with a vented crawl space in ages. I would aim for that vapor barrier and insulate the crawl space walls. I have even seen some people pour a slab over the crawl space. Makes it much nicer, cleaner and easier to store stuff in. If it is in the budget, I would recommend discussing the option with your builder.

We built on a 3'6" unvented crawlspace 3 years ago and poured a concrete floor in it and sprayed the concrete walls and rim joists with closed cell foam insulation. Our geothermal HVAC is in the crawl and everything stays dry and a pretty constant temperature in the crawl.

I'm with summersatthelake. here in my part of La. houses on piers

and even elevated homes aren't uncommon.

2-3" of closed cell foam

lsu ag center has a brochure insulating floors of

raised homes in hot humid climates.

great investment of $1. for folks in similar climates.

best of luck

We did what I think JDS described under the downhill segment of our house. Perimeter drains, vapor barrier and what the locals call a "rat slab" or 3" or so of concrete. Plus it is insulated, but not heated. Otherwise, it resembles a basement with 5 ft headroom! It should be useful for some storage that we don't want cluttering up the garage (which means probably stuff we don't even need). We have outside access that requires moving a panel, but also a "smuggler's hatch" type of door in the floor. OK, that part might be a little eccentric...

Rat slab being the thoughtfully finished floor you provide for the rats.

How much more would it cost to have a full basement? It that even possible given your soil? You could put the mechanicals down there, and you'd have easy access to the plumbing, electrical, etc. throughout the house, as well as having usable space.

"Rat slab being the thoughtfully finished floor you provide for the rats"

I think it's so they can't burrow under to get in. I assure you they can't get in through the metal siding or the concrete wall.

AKA rat barrier...