installing wood sub-floor over sloped concrete garage floor

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  #1  
Old 06-27-15, 08:15 PM
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installing wood sub-floor over sloped concrete garage floor

Not sure what forum section is best for this topic. Here's the scenario. A house was built over 70 years ago, as far as I know, with a single car attached garage. The concrete floor has some slope toward what was the opening to the garage. A former owner converted the garage to a room and installed carpet directly over the concrete. My son, who bought the house back in 2006, as I recall, removed the carpet, painted the concrete floor, and held it as a rental property but now wants to do some updating/repairs and sell it.

One upgrade is to install a wood sub-floor over the concrete floor so that the room has a level floor upon which to install some type of regular flooring. In addition to the slope toward one end of the room, the floor also has a bit of slope from side to side (see third photo below). Clearly, creating a level sub-floor in this situation will require some creative techniques.

I talked to one independent contractor today about the project. He mentioned using 2x4's and 2x6's and trimming them as needed to get a level foundation for the sub-floor (OSB or plywood). I think use of a larger variety of boards makes more sense, that using boards (trim boards, regular framing lumber, whatever) as thin as 1/4" and in wide range of thickness makes more sense. This situation does not require framing lumber with the strength to support sub-flooring over an open basement or crawl space. Shims can be used under boards as needed at any point on the concrete floor.

My son and I agree that keeping the new sub-floor as low as possible is desirable. One reason is to keep the floor at a fairly normal height in relation to windows. The room has 3 windows.

The outer walls have brick at the base of the walls and you can see it in the photos below. Our idea is to keep the top row of brick above the new floor as a rustic aesthetic element. So, at the highest point of the concrete in the upper left corner of the 1st photo, you can see that a 2x4, even laid on it's side there, would raise floor higher than we'd like.

I guess this might require thinking outside the box for some contractors and carpenters. And, I feel the guy I talked to today was not thinking outside the box. Seeking opinions ...

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Last edited by dderolph; 06-27-15 at 08:47 PM.
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Old 06-28-15, 03:40 AM
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What is the ceiling height, presently? Worrying about the brick design may be your nemesis, as it may need to be partially covered in order to achieve "level". One way out would be to pour SLC (Self Leveling Compound) over the floor and allow it to level the floor. Then you could apply an underlayment and click lock engineered flooring, NOT laminate. If you insist on pure 3/4" hardwood flooring, you will need to build a sleeper system, apply 3/4" Advantech subflooring, then your flooring, taking a hunk out of the height of the room, if it is 8' or less.
 
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Old 06-28-15, 05:54 AM
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Couple of strikes against you here. First is the painted concrete which may preclude the use of self leveling compounds. It may have to be ground down to bare concrete before application of a primer to prep for leveling. Second, you can not simply lay plywood directly on concrete. Untreated wood in direct contact with concrete is against industry standards. It will deteriorate/de-laminate with time.
 
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Old 06-28-15, 07:49 PM
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I measured the ceiling height today. In the center of the room, the ceiling is about 8'11". With the slope of the floor, the height is slightly less at one end of the room and slightly more at the other end. Anyway, this clearly means a false floor could be above the brick shown in the photos with no issues regarding ceiling height. The room has a ceiling fan in the center but it would still have plenty of clearance with a floor above brick line. So, I guess we'll drop the idea of keeping floor low enough to show one tier of brick. By doing so, that will make building a false floor easier, although it will still require cutting supporting boards at varying heights to create a new level sub-floor.

I am skeptical that self leveling compounds are a viable option, especially if paint would need to be removed from the concrete. I think that simply isn't going to happen. I'm not familiar with self leveling compounds but I have the impression using it to level a floor this size would require an awful lot of the compound. Also, the side of the room next to the kitchen does not have the same brick border and drywall on that side of the room basically goes down to the floor. So, I imagine some drywall would need to be removed at the bottom of that wall if self leveling compounds were going to be used.

The only other issue regarding allowing the floor to be built to a level about the brick line would be lower-than-normal height of bottom of windows from the floor. Will mention this point to my son and see what he thinks about it.
 
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Old 06-29-15, 02:35 AM
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I would have mentioned the windows, but couldn't see the tops of them, so it is not known what it would look like, aesthetically. Also, the floor would have to be prepped. I could not tell that there was paint on it, but good call by Z. You have the height to build a sleeper floor without hindering height, and it may be your best bet, taking into consideration the window ledge height, and your son's idea on that.
 
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