My (future) Studio Room has concrete slab floors (on top of compacted earth) and Cinderblock Walls. I plan on building a room within a room.
Hello gbondo9. Forget the subfloor(?) question for the moment. It is of no concern at this point. From what I understand about your situation, I think you need to realize some things. First, let me ask you if this is correct.
The ORIGINAL unlevel slab in the basement. Was this poured as an inherent part of the foundation footings or was it poured after, between the footings? Do you know how THICK this slab is?
This is where a planned "room in a room" scenario need analysis.
1. Why do you think you need it?
2. To correctly build a "floating room in a room structure" requires "decoupling" the existing slab at the boundarys of the proposed room. This can be done in a few ways. However, ALL of them require the supporting membrane to structurally support the ENTIRE WEIGHT of the room. Not an easy task. Should you build without addressing this issue from the beginning, you run a risk of cracking the existing floor, which may or may not allow moisture in, but it also may void any homeowner insurance should you NOT apply for a building permit. Room in room scenarios present MANY MANY problems, which from the inspection perspective, may set up potential safety concerns, if not downright disaster should something happen, like a fire.
But getting back to the floor, this is where PLANNING is of utmost importance. And in order to set up a decision hiarchy, we need to know tons of stuff. Personally, I wouldn't begin to suggest solutions till I see a plan with accurate dimensions, showing existing walls, doors, ceiling heights, and a section through the room showing the construction of the floor above, etc.
Reason is, decisions regarding the "room in a room" NEW ceiling, requires knowledge of how you are going to support this new ceiling. This decision alone will have a bearing on the NEW floor/footing support conditions. For instance, should you decide to use the new walls to support a ceiling structure, now the floor has to support this additional weight. Should you decide to "hang" the new ceiling structure from the floor above, the existing floor structure MUST be able to support this weight.
gbondo9, building a TRUE FLOATING ROOM IN A ROOM, is a lesson in reality checks if not a lesson in physics. Not only are you facing structural issues, but legal issues, HVAC issues, THRESHOLD issues(raised floors cause entry/egress issues should you build without addressing this from the beginning), decoupled wall sway issues, and most of all...FIRE BLOCKING ISSUES. Not to mention various THREE and FOUR LEAF transmission issues without a thourough understanding of existing construction.
This is not to say it can't be done, but flying by the seat of your pants with NO COMPLETE PLAN, is asking for trouble in my view.
And if you don't think so, maybe you should read this in its ENTIREITY.
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2921&start=0&sid=2870e07c90f0aad0da18e9bc1b1e820d
BTW, I saw your post at John Sayers, and I am supprised no one there has replied.
Lastly, should you simply lay a subfloor and build a "room within a room" directly on this floor, personally, I believe you are wasting your time. There are many other options for isolating this room to a degree, without building a room with in a room, if you even need it. That is the question.
fitZ
!!!!!
Talk about DIY? Let me tell you.