excellent post gygax!
my basement is not finished and the ground is concrete, which i understand absorbs heat and shows leo what you may be doing.
any ideas for raising the ground up? basically a floating room inside a room.
what helps making the ground perfectly level? this may be important for hydroponics. or do i not want perfect level for accidental drainage.
how much space between 2x4s?
would tyvek or insulation help odors/temp control?
I also have the unfinished cement floor basement.
you could frame out the floor and do some plywood, Home Depot also sells something called Dry Lock(?). They are in the lumber section. They come in 2x2 sections and it is basically for basements. It is particle board on top and plastic grooved on the bottom...it allows water to go under the floor with out touching the wood.And it is tongue and groove. You could also just throw down some carpet. Or perhaps some reflective material on the floor to stop the cement floor from absorbing all that heat.
Leveling the floor can be a chore, they do have cements for that, but just make sure that your wall framing is level with some shims and build off the base of the frame.... you are good to go.
Code on 2x4s is usually 16 inches, I do 24, but you can get away with whatever you want (although the wall could bow if you go with more than 24 inches between 2x4s...we're not to worried about code until we sell the house...right? You could even go a whole four feet but the wood will probably bow at some time...so I forgot to add more 2x4s to my idea above....woops! So building this room would actually require 6 or so 2x4s per wall.
I also use tyvek (reflector side facing into the grow room) to improve the lighting...not sure what this does to the temperature. Not sure that it does anything for odor control but there are many DIY odor control techniques on this site. Look for the DIY carbon filter post.
I am by no means an expert but I have a room similar to what I have posted above.