# Laying Floor Joist directly on conctrete



## K2

drbrsjr said:


> K2, I'm still around. I was planning on digging out my garage floor for access to the mechanicals but it doesn't seem to be a very popular idea. I was concerned about screwing in a ledger on the existing garage 2x4 walls for the floor joist to sit on. It doesn't seem sturdy enough to me. I thought I might build a wall inside the existing garage wall or build up the floor on posts on top of footers and beams like I would build a deck. I want to run heat runs out to the new additional living space and water/drains as well. I have also been told that I need a 36'' crawl space by code in my area. Any advice? Thanks from Columbus Ohio.


I would lag a rim joist/ledger to the 2x4 wall and hanger off that rim. . 3 (3/8 x 5) 16 " on center should do it but someone should really do a little math on that. I have a calculator around here somewhere but there may be one on line. You could throw a few flat kickers under the rim down to the foundation but that really should not be necessary. That part of it might be the same even if you were doing an inaccsssable crawler.


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## Charlie Roseman

Spammer Post - Content Removed.


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## pfloyd

Ignore.


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## pfloyd

Sorry. Wrong thread.


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## moldbuster

Depending on your soil/moisture conditions, a vapor barrier may cause problems too. Remember, vapor comes up and then stops on the underside of the vapor barrier...but then where does it go? To the edges of the room typically where it collects, finds a way in and causes mold. Before you put on a vapor barrier, cut back on the vapor coming up from the concrete to begin with. I like Kryton. THEN put your VB and treated sleepers down.


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## D MAN

pknyryan said:


> Can you not eliminate "touching" the garage floor at all and simple secure a 2x8 to perimeter walls and use joist hangers to build a deck sitting approx. 1.5 to 2 inches above garage floor. This will eliminate the need to worry about shimming an uneven floor, vapor barriers, ect. I would apply a dry-lock type "paint" to the floor, install the floor, insulate it with polystyrene, cover it with 23/32" T&G flooring (glued and screwed) and apply desired fininsing (tile, carpet, ect).
> 
> I am assuming your exterior walls in you garage are dimensional lumber, altough a similar system would work with CBS type construction using PT lumber and "tapconning" it to exterior walls.
> 
> I would be hesitant to rely working off a poured concrete floor as they are rarely level, and inherently not designed to allow for a floor to be built on top of them. If the floor happens to selttle, crack, ect, what happens to your new floor? (imagining floor tiles cracking of poppoing up) At least when using the exterior walls to support the weight, you have the added assurance you are transferring the load to exterior walls, which theoretically are spported by a footing and designed to carry a load and resist settling.


this would be the way to go, vapor barrier on concrete, insulate between joists.


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## ubcguy

what most are suggesting is a sleeper floor. another thing you can do is scribe 2x12's or 2x10"S to the floor accounting for sub and finished floor. personally i would install a computer floor. they are easy to install using hand tools and a hammer drill along with a laser. it is a commercial floor product, but you will thank me in the long run trust me


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## van-island

pknyryan said:


> Can you not eliminate "touching" the garage floor at all and simple secure a 2x8 to perimeter walls and use joist hangers to build a deck sitting approx. 1.5 to 2 inches above garage floor. This will eliminate the need to worry about shimming an uneven floor, vapor barriers, ect. I would apply a dry-lock type "paint" to the floor, install the floor, insulate it with polystyrene, cover it with 23/32" T&G flooring (glued and screwed) and apply desired fininsing (tile, carpet, ect).
> 
> I am assuming your exterior walls in you garage are dimensional lumber, altough a similar system would work with CBS type construction using PT lumber and "tapconning" it to exterior walls.
> 
> I would be hesitant to rely working off a poured concrete floor as they are rarely level, and inherently not designed to allow for a floor to be built on top of them. If the floor happens to selttle, crack, ect, what happens to your new floor? (imagining floor tiles cracking of poppoing up) At least when using the exterior walls to support the weight, you have the added assurance you are transferring the load to exterior walls, which theoretically are spported by a footing and designed to carry a load and resist settling.


This is what I did when finishing a garage into a master suite. The foundation walls came up above the slab about 10-12", so I lagged the 2x8 rim joists into the concrete and suspended the joists over the slab by a few inches. Before the joists I laid down a poly vapour barrier and also sill gaskets under the rim joists.

I then put fiberglass batts between each joists (suspended with a plastic mesh stapled to the joists so they don't fall down) and overlaid it with 3/4" plywood, then 3/4" solid hardwood on top.

One thing I didn't do was vent the 2" gap under the joists, but there was previously an uninsulated/no vapour barrier sleeper floor there previously with a 2" gap that was in place for 15 years with no issues (apart from being very cold!) 

The garage slab ranges from about 4" above grade to 3 feet above grade (the property is sloped) so there isn't really a moisture issue, but I am still worried a little bit because I didn't vent the 2" airspace... but I considered it similar to the air space in the sleeper floor, so hopefully no difference and no issues...?

Can anyone ease my fears about not venting the gap in the same way as a typical crawl space would be vented?


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## Mellissam

I think with the VB laid down (taped and sealed), there will be no issue...no moisture laden air to condense under joists. 
Can always scope it after a while to see if there is any moisture issues. 
I had a house once that was on piers, and the underside of joists were sheathed and seams caulked (i.e. airtight from below...well, the perms may not have been 0 given it is plywood, but you get the picture... )
At any rate, after three years, I had to remove a piece of sheathing. Everything was bone dry and no signs of moisture issues.


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## JCthatsme

I would 
1. Lay DPM, folding up the walls 10"
2. Lay 50mm Celotex down for thermal values
3. Use 6x2 joists hung of joist hangers around room perimeter
4. Deck to ffl


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