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Old 04-04-2011, 11:12 PM   #1
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Bearing surface for joists - home addition


I'm building a 25'x35' addition to my raised ranch with a walk-out basement. When I removed the siding on the side of the house where I'm building the addition, I didn't find a rim joist. I saw the ends of the floor joists resting on two 2x8s on end. The 2x8s are tacked to the CMU wall with tiny gobs of mortar (no sill plate).

I want the ceiling in the new basement to be a foot higher than the ceiling in the old basement. To gain 5 inches, I planned to drop the slab in the addition so that it rests on the footing. I planned to gain another 7 inches or so by raising the floor joists in the addition.

Whether or not I raise the floor joists, I don't see any way to support the ends of the new floor joists where they meet the old structure.

1) Could I build a stud wall directly over the 4" footing projection to serve as a bearing surface for new floor joists?

or

2) Could I nail a ledger to the 2x4 studs to support one end of the 23' floor joists? What if I attached the ledger to blocking in between the studs?


Last edited by benjamincall; 04-04-2011 at 11:28 PM.
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Old 04-04-2011, 11:48 PM   #2
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Bearing surface for joists - home addition


I would ask your local B.D. about your intentions...... You may not be able to drop the slab...Let us know what they say.

Gary

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Old 04-04-2011, 11:58 PM   #3
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Bearing surface for joists - home addition


Here's a fellow with a similar question:

http://concrete.com/Forum/ubbthreads...t&Number=14343

His addition appears to have lower joists than the existing structure. Mine would be higher.

Gary,

What sort of issue might preclude me from lowering the slab? I'll let you know what the BD has to say.

-Ben
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Old 04-05-2011, 09:12 AM   #4
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Bearing surface for joists - home addition


Simply put, you can't place the bottom of the floor lower than the top of footing w/o some substantial additional work.

You can build a load bearing wall off of the existing footing if there is enough footing left. You won't be able to verify this until it's excavated unfortunately. I would recommend setting a course of 4" (for a 2x4 wall, 6" fro 2x6 wall) half course solids directly on the footing to get the wall to top of floor level.
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Old 04-05-2011, 12:15 PM   #5
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Bearing surface for joists - home addition


Quote:
Originally Posted by jomama45 View Post
Simply put, you can't place the bottom of the floor lower than the top of footing w/o some substantial additional work.

You can build a load bearing wall off of the existing footing if there is enough footing left. You won't be able to verify this until it's excavated unfortunately. I would recommend setting a course of 4" (for a 2x4 wall, 6" fro 2x6 wall) half course solids directly on the footing to get the wall to top of floor level.
The bottom of the new slab will rest right on the top of the footing. The bottom of the existing slab is another 5 inches above the top of the footing, so that's as much ceiling height as I'll be able to make up.

I excavated the footing myself, and I found at least four inches of footing left. So, you're suggesting that once I've placed the concrete for the slab, I should mortar 4x4x16 CMUs on top of the slab over the footing?

That other guy's drawing doesn't show the new slab he intended to build on the outside. My basement addition differs from his drawing in that my new basement ceiling will be higher than the 7' ceiling in the existing basement. Could I use a double 2x4 top plate, 92-5/8" studs, and a single bottom plate resting directly on the slab over the ~4" footing projection? What benefit would the half-blocks provide?

On a side note, I'll probably use the existing first floor wall to support the roof of the addition, so the weight of the roof will rest on the existing CMU wall, not the stud wall built over the toe of the footing.

Last edited by benjamincall; 04-05-2011 at 12:20 PM.
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Old 04-05-2011, 05:35 PM   #6
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Bearing surface for joists - home addition


Quote:
Originally Posted by benjamincall View Post
The bottom of the new slab will rest right on the top of the footing. The bottom of the existing slab is another 5 inches above the top of the footing, so that's as much ceiling height as I'll be able to make up.

That's fine, the slab should really be directly on the footing.


I excavated the footing myself, and I found at least four inches of footing left. So, you're suggesting that once I've placed the concrete for the slab, I should mortar 4x4x16 CMUs on top of the slab over the footing?

That other guy's drawing doesn't show the new slab he intended to build on the outside. My basement addition differs from his drawing in that my new basement ceiling will be higher than the 7' ceiling in the existing basement. Could I use a double 2x4 top plate, 92-5/8" studs, and a single bottom plate resting directly on the slab over the ~4" footing projection? What benefit would the half-blocks provide?

You can set it on the block OR skip the block and set it directly on the slab. Putting the block in first would allow you to build the wall, floor system, pretty much the whole addition before you needed to pour the basement floor.


On a side note, I'll probably use the existing first floor wall to support the roof of the addition, so the weight of the roof will rest on the existing CMU wall, not the stud wall built over the toe of the footing.
I can't tell you how much the 2x4 wall can carry, only that it's an option to consider in the pre-planning. You should really have someone with the proper background (not the web) verify this on your print.
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Old 04-05-2011, 05:49 PM   #7
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Bearing surface for joists - home addition


Thanks for the quick response. Clever idea about the concrete block.

I think you've answered my main question about whether or not I could build a bearing wall over the footing toe. I just wanted some validation of my idea. The PE who's helping me out with this project has more background in mechanical engineering than civil engineering, so I appreciate feedback from a guy who has some practical experience.

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