If the OSB was glued down with proper subfloor adhesive and then nailed and screwed tight, no it will not pull off. Drywall deliveries to a basement are often put through a removed section of subfloor. Doesn't work when it's properly adhered. (OTOH, I once saw a builder use white glue as adhesive--the stuff your kids use on kindergarten projects. Likely a different story.) R and R an existing hardwood floor will be very expensive. Many of the boards will be destroyed and useless. Let alone the double labour. If you still insist on that, add a layer of plywood. You can transition the added height to the hallway. However, for the hallway the stair problem is nearly insuperable. As Reno8 suggests, work from underneath. Blocking, nailing and screwing may do the trick. The fault here, as you note, is your last minute change from carpeting to hardwood. This post was edited by worthy on Mon, Aug 4, 14 at 13:51

If the support for the floor flexes the concrete will crack. Without knowing joist sizes, spacing, and span there is no way for anyone here to tell. Flexible membranes ans cement board are used to isolate tile from any minor movement of the floor deck (like from humidity or a a concrete floor cracking) and do nothing to prevent cracking if the joists are not stiff enough for the load.

First, I would properly test the concrete for moisture vapor emissions(vapors cannot be seen or felt) I would then flatten the concrete substrate to the strict manufactures specification of 1/8" in 6 feet, Some, like Owens Plank, is 1/8" in 8 feet. Use a straight edge 8 feet or longer to varify. A stretched string line can also be used, to tell you where you need to grind down the high spots first, and fill the low spots. Now your substrate is prepped, you may need a troweled on moisture barrier membrane, if the concrete tested high for moisture vapor emissions. Following the directions to the letter. Now, all the doorjambs need to be undercut, so the flooring slides beneath them. It looks hacked in when I see someone try to cut around door jambs and trim it out with shoe molding... TACKY!!! Now, find your longest straight wall in which you plan on starting from. On both ends of the starting wall, dry lay about 4 or 5 rows, if it is plank flooring, and about 10 if it is strip flooring. And push them up to the wall and adjust for your expansion gap. Make a mark on the substrate. Do the same on the other end of the room. Now pop a string chaulk line, between your marks. That is your straight, and square starting line. Now, trowel out your glue, making sure you have a rag with mineral spirits on it, handy to wipe fingers and any smudges of glue(this is where most pros and DIY'er mess up and get glue everywhere) Spread/comb out, the adhesive, not leaving any big blobs, not going over your popped line. Don't get so much glue spread down your run, that it sets up before you get wood into it. Since this is your first time, about 10 feet spread in your popped run at a time, and then finish spreading the area, when you get down there to it, and can't go any farther until you do. Work your way from your line back to the wall, using blue tape, to keep it all tight. Once you get that band completed. Measure out so you can pop another line, but this line is just a glue control line. Measure out about 2-3 feet at a time, so you can reach across or jump across your spread glue, if needed. Once you get going, production will go faster.

Whatever you do, dont do a slab! My parents house has a slab and it's increadibly inflexible. If you have sand or clay, you can get settling issues over time that are very hard or very expensive to fix. Plumbing problems? Have fun not only tearing up your floors but breaking up and replacing concrete. Very messy! If my father had it to do over again he would never do a slab but a crawlspace or basement. If you have clay, especially with the tempurature flucations you get in Canada - well, good luck with that. With a crawlspace you can easily deal with any of the issues that were pointed out above. Foundation settles? You can relevel your house pretty easily since it's "floating" on the peremiter foundation. And just because you have a slab doesn't mean you can't have moisture or radon problems either - and if the builder gets the slab wrong you are faced with a very messy and expensive fix worse than if you have a plumbing issue. I'm puzzled with your mentioning a basement - if you have a basement, this is all moot - there is no slab except for the basement floor. You don't want to do a crawlspace under a basement floor - ventalation would be insane. But I would do a thermal break - vapor barrior and 2" - 4" of rigid foam before pouring the basement slab. Better still, since you want to finish the basement embedd radiant heat in that slab that's on top of foam. I'm thinking about re-doing the floor in my basement to get radiant heat - it's awesome! If you do go basement or crawlspace, be sure the builder is using engineered joists for the sub-floor. Read the manufacturers guidance for the maximum size of holes and minimum distances between multiple holes through the webbing or center of the joists. Manufacturers provide this information for a reason - improper holes through the joists dramatically compromise the structural integrety of the joists which leads to at best overly bouncy floors, at worse floors that collapse! Be very wary of plubmbers and HVAC contractors - they often hack through structural members with impunity. Hold your builder accountable to maintaining the recommendataions of the manufacturer of the joists (or any other product) and NOT CODE! Get it in writing! Code is the MINIMUM - but you want your minimum to be the manufacturers guidance. I had to put up an extra knee wall in my basement to strengthen a floor that was weakened due to an overzelous HVAC guy that destroyed two joists routing the fresh air intake for my furnace. Learn from the experience of others. If you can find a home inspector that actually knows building code and has experience with engineering, stipulate that you will do your own pre-drywall structural inspection and then final inspection with your own inspector. Trust but verify... Good luck! Just don't do a slab ;)