I'm getting ready to partition and refinish a portion of my basement using steel studs. The basement boundary walls are block and because of existing plumbing and other services, I'll be framing my finished walls anywhere from 6-10 inches from the block in all areas. I plan to insulate the walls with R-13 batt but one of the issues I'm a little concerned with is the floor. I'm dealing with a low overhead so I don't have the height to install a subfloor above the poured footer - even a few inches - and put foam insulation beneath it. So, it brings me to the first of three sets of questions:

1. Are there any alternatives that would provide me some insulating capacity for the floor without diminishing the clear headroom? Should I be concerned about loss through the floor if I plan to just put carpet down, maybe an under-pad? By the way, I'm in SE PA and the basement is dry.

2. If I use R-13 batt in the finished walls, do I need to include a separate vapor barrier or is the batt facing good enough? Should I be doing anything in way of insulating the block or the back side of the walls if I have an relatively large air gap between it and the walls?

3. Maybe not for this forum but when using a steel framing system, should I put a PT sill underneath the lower wall track or should I mount the track directly to the footer? I found a few conflicting thought on this - a PT sill between the footer and the lower (steel) wall track could actually introduce a corrossion mechanism . . . a PT sill guards against lower track corrosion by adding a "buffer" . . . which is it?

Thanks in advance for any advice you can give.

Start with the walls.

Before you do anything. If you have not had one done. Get a radon test performed. Your area of the state is in a tier one area. This means you have some of the highest radon levels in the country. A test should run in the area of $100 or so. Have it done professioinally Do not use the kits supplied by the home centers to save a few bucks. They are worthless.

Yes you MUST install a treated lumber sill on the floor. Otherwise the corrosion with the cement and steel stud will eventually rust out the metal. Besides it is code. Which I assume you will be pulling permits to do this job.

Be sure to use the proper fasteners to hold treated stud to floor. New pressure treated studs contain chemicals that will eat away standard screws and nails. We use asphalt paper on top of stud to ward off any issues that may arise because of the metal/wood contact. However I have not read or seen any concerns about this subject anywhere else about this happening. But the cost of the paper is nil compared to what it would cost to fix later.

Insulate the walls with unfaced insulation. Using faced insulation is sort of a pain because you need to have a complete vapor barrier (sealed tight) for it to work properly. Very difficult to do with metal studs.
Then use six mill plastic and fasten it tight to the top plate along the ceiling area and drape it down and seal it tight to the wood plate along the floor. Cut slits in the plastic around the electrical boxes and stretch the plastic over them tightly. Do nothing to block walls behind the new wall.

Install the wall.
Be sure to kick the wall board off the cement floor to prevent any wicking of dampness into the wall material. We use the new fiberglass sheetrock sold at Lowes as it does not get effected by moisture and does not support mold. A few dollars more but worth it.

When we construct or re-construct a basement we always install a ventilation system behind the walls. Humidex makes one, but we build our own. What it does is draw conditioned air from the living side of the room and pump it outside of the house through a dryer size vent pipe. We construct ours using a radon fan. Only about 250 CFM max. This device takes out any moisture that has not yet condensed on surfaces and dumps it outside. Be sure however to have enough make up air. Draw the air from the 1st floor level through transfer grill on basement door and through wall of new basement.

Floor.
How high is the ceiling in the basement?
As a mold remedation contractor and tester I would stay away from any carpet on the floor. Unless you can remove it and have it cleaned outside of the home. Regardless of what you think. There is some dampness in the floor that you do not see. This dampness can and does support dust mites and a host of other critters that could be used in a godzilla movie. Placing carpet like this only provides a place for them to survive. My suggestion is to lay tile on the floor. Use electical heat mats under the tile to keep areas such is front of couch, tv, play area etc. warm. These do not cost a lot nor cost a lot to run. Once the tile is down then smaller area rugs can be used for additional softness and sound dampening.
If you must use carpet. You can use these new wood squares sold at Home Depot and Lowes. They are 24" square, interlock and have a plastic vapor barrier on side that is placed on the cement. The dimples on these pads are supposed to allow for ventilation below in case some water gets under the floor. These must be placed on the floor BEFORE you install the new walls as they will be placed on top. Using these you will not need the treated sill. Once installed you can carpet as desired. You will loose about two inches of height once placed and carpet is installed.

Thanks HCC! This really helps! I'll certainly be putting permits in-place and I already have a radon mitigation system installed and running.

Got it regarding a PT sill and asphalt paper. I'll be sure to work that in.

Floor to the bottom of the overhead joists is only about 81 inches and I'm looking at losing a few inches of that because of some copper pipe runs and a low-profile ceiling tile system.

My primary purpose for finishing the basement in the first place is to create a play room for the kids and as such, I'd really like to put carpet down for a numbe rof reasons. Can I line the floor with the same 6 mil plastic I'll be using on the walls before putting carpet down?

By laying down plastic on the floor before the carpet goes down is a mistake. It will trap moisture below the plastic and can cause the plastic to fail. It will also cause the carpet padding to slip and the result will end up being a carpet that looks like it was not properly stretched.
If you must use carpet only, again not my first choice. Be sure that the carpet folks use a carpet pad that is designed to be used below grading in basements. Felt pads will soak up moisture and will cause all kinds of health issues. Some pads are treated with anti-microbial coatings that help resist development.
Keep the carpet vacuumed daily. Stay away from carpet cleaners and chemicals that you spread on the floor and vacuum up later. Do not use commercial cleaning companies that use water or those who use chemicals to clean the carpet. The water will feed any mold spores that have settled on the carpet and the chemicals used will never be completly vacuumed out.

Things you must understand.
Children breath in air from a diffrent level as adults. They spend a lot of their time on the floor laying down. Any mold or dust mite feces that collects is quite easily breathed in by them because of this. This is why I always suggest that the floor be tile or wood. Much easier to clean and much more healthy for the kids.
Need more info, Pick up the book called " My House Is Killing Me" written by Jeffrey May. It will shed some light on how to maintain a healty home. Might even scare you a little. But once you read this book you will understand at least how to do things a better way and may make some changes on your life within your home.
As far as the radon system is concerned. If you did not have the radon checked in the past few years do so. Radon levels can change. Having a base line number and checking it from time to time is a prudent thing to do.

My only question is why you would want to use metal studs rather than wood ones? Are they required by the local codes where you live? I would be concerned that the high moisture in basements would eventually cause the studs to rust.

My daughter has what is essentially a converted "basement house" (the "first floor" is actually a walk-out Basement!)that we're in the process of completely gutting and re-habbing because so much of the previous work was done so lousy.

In our case, there is a perimeter waterproofing trough that is at the joint between the cement block wall and floor to ensure there is no leakage. We then painted two coats of mold resistant foundation paint by Zinsser on the walls, then tacked bubble foil insulation at the sill plate and let it hang in front of the wall. We then studded up walls (using treated plates on the floor) and installed mold resistant insulation between the studs and are using the new mold resistant sheetrock on all exterior walls and the lower 4' of the interior walls, just in case.

We are installing 12X12 quarry tile installed with thinset mortar directly on the cement floors throughout, except in the living room, we are using plastic laminate flooring over dimpled plastic panels to keep the floor elevated in case of moisture.

I'd never seen nor heard of a ventilation system that was described above before. While it sounds like there is obviously some merit to it, I would wonder about the amount of heat loss there would be from running such a fan constantly? I wonder if installing a humidistat to control the fan would make this more cost-effective, so it's not running 24/7/365?

HTH!