Expert: Dave Johnson - 2/27/2009

Question
QUESTION: I have an existing 10'x 30' wood framed extension on my CBS home.  The slab in in good shape.  The addition was done with 2 x 4 construction and does not have enough insulation and this room is harder on the A C unit and the hottest room in the house.  I want to add another 2 x 4 framed wall and scap it onto two  of the existing outside walls of this addition.  I will need to extend the slab about 4 to 5 inches to sit the 2 x 4 base plate for the extended walls.  Would it be o. k. to drill into the outside of the exiting slab and insert rebar to add four or five inches to the slab or should I dig down into the ground and form a footer for this framing.  I intend to use 5/8 inch PT plywood sheating and then wire lath and stucco the new ouside walls.  Thankyou, Ray

ANSWER: Hi Ray,
The answer following is assuming you're in a climate where there is no frost movement.

What about this: Attach all your new studs directly to the existing studs, (screws or well nailed) and not even have an addition to the slab.  Of course you'd have to still have top and bottom plates and those too, would be well nailed.
I say this because I don't really think the attached concrete would have all that much strength anyway. (the drilling and re-bar you mentioned would have to be done every 12" or less to be effective.)

If this is not enough, or not what you want, please mail me again...
best of luck,
Dave




---------- FOLLOW-UP ----------

QUESTION: Dave,  Thankyou for the reply.  Yes I am in a warm climate, S. Fla.  My reason for the extended slab to place the botton plate is not for strength. I've had problems with this with termites in the past and I really don't want the exposed wood directly above the ground.  This might be a problem with insects, we do have a problem with ants also.  I thought the concrete lip or extention might provide an easier tranition to the stucco surface that will be applied over the sheathing.  You mentioned the rebar at 12 inches or less.  What other concerns would I have. This is such a small addition to the slab. It will probably look more like a curb.  What would you suggest for rebar size.  What size holes do I need to drill, how deep.  Should I use apoxy to hold them.  I don't have much experience with forming concete.  What I would like to achieve with all of this would be to have this addition appear to have been constructed with concrete block rather that stick built when I'm done. Open for ideas.
THANKS AGAIN!  Ray

Answer
Hi Again,
I see.
Then your idea is okay, too. But I would still attach the new walls to the existing....
Drill 1/2" holes and use #4 re-bar. You don't need epoxy, just drive the bar in, and have 4" in and 4" out.
You might want to use a hammer drill, it will be a lot faster and easier than a regular one.

If the stucco is going down onto the new slab, put a few anchor bolts into the new pour so you can attach them to your bottom plate. This will help keep any separation between plate and slab.
This may sound like overkill, but better safe than sorry.....
Best of luck,
Dave