Another Wood Subfloor Over Concrete Slab

GreenBuilder

I have a situation similar Larman's thread in this forum (evidently I'm not allowed to link to it here, sorry), although I have less room to work with. The house I'm working on has an attached 1-car garage that was converted to living space by a previous owner, details unknown. Upon pulling two layers of 1/2" untreated OSB subfloor, I discover a 2x4 PT joist system sitting directly on the slab, with faced fiberglass batts, paper side up, in the spaces. No plastic, hot mop or any other type of vapor barrier is visible. No idea what's under the concrete slab.

Still waiting on the local codes officer to interpret IRC and tell me if I need to ventilate under the subfloor or maintain a minimum clearance. Getting a skid in to dig out the floor is not an option (no more garage door of course).

I haven't torn into this situation real deep yet, so I can't even see how well the slab perimeter is insulated or sealed against the block & mortar foundation wall.

Reason for tearing into this was suspicion of mold after seeing some water damage near the floor on each side of an exterior door, and the floor had all kinds of peaks & valleys in it. Now that it's opened up, the floor actually looks quite dry, and with the exception of a little bit of black on the ends of the batts right up against the wall under the door, everything looks real dry & pretty. Inside the bottom of the walls on either side of the door is a different story, as a few critters & insects (fortunately no house eaters) decided to take up residence (eviction notice served). The 2x4s are not shimmed or cut to compensate for the slab uneveness, which explains the irregularities up top.

So I'd like to get a vapor/radon barrier down, and I'm thinking one of the best options is to apply a liquid waterproofing material like Sanitred (www-dot-sanitred-dot-com/basementfinish.htm again, too new to put an actual link, sorry) to the slab, even working it down around the slab perimeter to get it good & sealed. Then shim PT 2x4s to flat & level as a joist system, and insulate the cavities with rigid foam board. Replace the two layers of 1/2" with a single layer of 3/4" tongue & groove. Finished floor's gonna be laminate wood, so I'll float it on top of a vapor barrier underlayment.

If the codes officer comes back to say I can't have an unventilated joist system, then I either pour a second slab over the first, or how about this: pour some leveling compound down on the existing slab, then the waterproofing compound, then two layers of 2" rigid foam, followed by the subflooring?

Any ideas much appreciated. Need to get moving on this quickly.

neolitic

http://www.contractortalk.com/f3/laying-floor-joist-directly-conctrete-31334/
There you go.


Don't know what your building dept.
will have to say, but I have had good
results with 6 mil vapor barrier, shimmed
joist, foam between, and T&G.

(Some folks from Colorado will disagree.)

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(Sorry....it seems there really are dumb questions)

genecarp

if the floor looks good , why mess with it? if ther is no dampness or moisture problem, why all the work? there is probably a vapor barrier under the slab if the room is as pretty as you say. dealing with the front wall is something you should do, unless your going to rip out the whole wall, fill in the gaps with pl or foam, make sure exterior grades away from building. get it done, plane or shim existing beams before sheathing.

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GreenBuilder

Getting to the toe plates on the walls, and inspecting the edges of the slab required removal of the 2x4 joist system, at least around the perimeter, which pretty much results in removal of all the interior spans as well.

Now that I've exposed the bottom 2' of wall studs all the way around the room (plus pulling all the insulation out), I see all sorts of new problems.

1. All sill plates are untreated pine, many rotted out.
2. Some of the studs, particularly on either side of what was the garage door and what is still an exterior man door, are rotted out.
3. On the two external walls of this room, the top of the foundation block walls are, at best, even with the exterior grade. The sill plates & studs sit on top of this, with blocking between the studs to serve as a perimeter form for pouring the internal floor slab. Thus the top of the slab is a good 4" above the top of the foundation wall, and the edge of the slab is either exposed to the wall cavity (where the blocking is missing) or still up against the untreated blocking, with no foam between.
4. No foam between the slab and the block wall on the house side that tops out about 18" above the slab.
5. No foam between the slab and an adjoining slab in the original finished part of the house (a den) that is 6" higher.
6. The main garage door was filled in with 2x6 untreated framing, sheathed in 1/2" untreated plywood, then covered with brick veneer up to about 24" or so. Three large casement windows take up the middle, and painted plywood serves as siding from the top of the brick up to the soffit. The entire wall under the window needs replaced due to rot. There is no moisture barrier between the brick veneer and the rotted-out sheathing.
7. On the corner to the left of what was the garage door opening, the corner studs and the jack/king studs for the garage door header are rotted back a good foot or so. Where they came down to the foundation (which is basically now a ledge 4" below the slab), there's no evidence of a sill plate anchor. Also, there appears to be about a 2-3" gap between the inside of the brick veneer and the foundation wall, potentially all the way across the front of the "garage", and at least a foot deep. I guess because the slab was poured to have a bit of a lip that extended 2-3" past the foundation wall. I have no idea what the brick veneer is sitting on. A photo of this (geez this link prohibition is a PITA) is at http: // i181.photobucket-dot-com/albums/x277/dtnicks/IMG_1678.jpg

So now I'm trying to figure out how I want to create an acceptable surface in this corner for the new sill plate that will go in (e.g. pack this cavity with concrete, trowel flush with the slab? Do I need to pin the joint with the foundation blocks below?)

Also, I feel like I should be doing something to seal & insulate the edge of the slab facing the exterior walls, plus maybe sealing the slab to the foundation wall, and, of course, taking measures to prevent water from penetrating the siding.

Any suggestions would be much appreciated. Looks like it will be a while before I need to figure out that flooring situation