Can concrete floor be poured separately from walls and how to brace them.
I am pouring a ‘guest room’ in a basement buildup. Does it matter if I pour the wall and slab separately? Is one order better than the other? 3 walls are retaining walls 6′ tall and 8″ thick. I am concerned about how to brace the walls. I thot maybe using diagonals bracing into an unpoured floor first? or I welcome suggestions on how to do this. The engineer is calling for a 1 1/2 deep footing extending 4’8″ into the slab area for San Bernardino County, CA. Does this sound normal?
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if an engineer has proposed a footing then he must have been provided more information than you are giving us... a 4'8" wide footer seems excesive but he must have his reason.
i would follow his adivce on how to achieve your desired final product.
It's a little unclear what you're doing, but I'm not sure I've ever seen a basement floor poured at the same time as the walls.
That is an awfully wide footing. Sandy soil?
Footings
Those footings don't sound too excessive for a 6' retaining wall in So. Cal. You would have several options as far as pouring order. I assume that a lot of steel is also called for by the engineer. From what you say this is a poured in place wall and not a block wall. A block wall would certainlly be easier.
You could pour the footings 4" below the slab level, then pour the wall, then the slab. Or, you could pour the footings and the slab together stub out the steel and then pour the wall. I would not suggest pouring the footings and the walls in one pour, that invites all kinds of problems. Bracing should not be an issue because pressure of the concrete in the forms will be the same on both sides which should be tied together inside the wall. This will require enough room behind the walls to build and strip the forms as well as water proofing later and the back fill. Plywood forms would be almost unusable afterward.
Either of these methods would work with a block wall, which would have the advantage of not needing as much room behind it, as there would be no forms. It could be water proofed as it was built. It would require the additional step of grouting it solid, normal procedure in So. Cal. .
My own choice would be ICFs. You could pour the slab and the footings in one shot. Put in the ICFs from the inside and waterproof them at the same time. Bracing could be either to the slab or the unpoured floor if you choose to pour the slab later. Minimum excavation and backfill. No forms to strip, no wasted lumber. 2x Bracing could be reused. Once you've poured the walls you're done.
Why wouldn't you want an 8' wall. With 6' you'll need to build a cripple wall on top. (I guess to be PC I should say a disabled wall.)
Off top of head with many assumptions. first is that "1 1/2 deep footing" is feet.
Let us first assume the sanberdo Soil liquifies during yer next 7.2 earthquake.
So, a bending moment of about 200 ft-pounds per foot length of wall, needs about a 1/2" or larger rebar 2" in from outside of form every 18 inches or less, or equivalent
Is that about what your plans call for?
You can pour the footing and wall and floor all separately, just dont have any dirt in the joint, best to pour a few days apart at most.
Wall bracing is anything you want, a 2x4 diagonal to a stake in the ground in the floor or outside the excaviation is what I've used.
Walls and Floor MUST be Separate
Hope you like digging!
What you have to do is excavate - a lot - completely dig down all around the room, within the walls. Then, one short section at a time, you pour the footings uncer the existing walls. That's step #1.
Next, you run whatever drains, etc., that you need to run in the ground.
Once the walls are supported, you fill, compact, and grade the dirt floor. Now you're ready to set up and pour the floor. The floor pour is usually tied to the footings by iron bars you drill for, and epoxy into them.
As for the walls themselves ... you jack the house up slightly, build the walls, then lower the house onto them. Again, the walls are tied to the footings with rebar stubs.
Overall, this job is best done by someone who know what they're doing. Mike Holmes has several episodes (Holmes on Homes) where various parties made a mess of this job.
Fully agree with Mike
Assume you want to keep the walls at partial height (6')...you have now created a retaining wall that has no means of resisting overturning pressures caused by the soil behind the wall except the footing design. The wall is acting like a vertical cantilever with the earth backfill putting tremendous pressure along the wall....trying to push it over.. And you have nothing at the top of the wall to resist these forces.
Assume you want to built the concrete walls to the bottom of the floor above (8' high or so)....now you have something that can resist the top of the foundation wall from turning over - the floor framing and plywood sheathing diaphragm. Instead of a large cantiliver, the walls are acting more like a sideways beam spanning from the basement floor to the first floor framing. The forces transmitted from the backfill are now distributed from the basement wall to this diaphragm and throughout the entire house...making the house work more like a big block in the ground instead of a bunch of retaining walls all trying to tip over. Also, there is not the need for a big footing - it's main purpose now is to transfer the vertical loads to the gound below...a much smaller footing is required - something more like 2' wide and a 8" deep. The concrete basement floor works to prevent the bottom of the basement walls from pushing in - much like the floor framing above prevents the top of the wall from tipping over. Overall, a much more effecient way to build a basement.
Am thinkin' what OP didn't say was that the 6 ft wall was where he is DIGGING OUT from under an existing 18 inch or 2 foot old foundation?
True or false ????
Guest room
Additional info. Junkhound was correct. On one side I am tying into an older foundation. Any suggestions on how to do that? Maybe a bolt epoxied into the foundation? The other side of the room will be a freestanding wall that will parallel existing piers that run through the center of the house. Where I save on this is to act as my own contractor. I have inexpensive competent help if I can tell them what I want done. The steel in the walls is #4 rebar forming 12" x 16" grids. None of the walls are loadbearing. The house is on a slope so while the back wall is 6' by 13' the side walls are staggered following the slope. A 6' tall 4' long section, then a 5' x 4' section all the way down to a 2' x 4' at the end. The fourth wall will be anchored to the slab. And the retaining wall schedule does call out for progressively smaller footings.
Footings first....
Specific answers to your questions:
Cast the footings first, then the walls on top of the footings, then the slab...then wood frame walls. This allows you to stage one pour atop the other and work off the surface below. When footings are done, vertical rebar or dowels for walls would be sticking up from the pour...you would build walls around this steel. Engineer might also require a notch installed in the footing below the wall to prevent the wall from slipping laterally under load. You need to review your waterproofing details here as well..is there a need for any additional waterproofing at this wall-to-footing joint? Finally, pouring the slab last allows you to concentrate on getting a good finish with minimal coordination of reinforcing or anchor placement. Any other method is not for the beginner...you can get in trouble in a hurry complicating a relatively simple process.
Also, normal attachment to existing concrete wall would be holes drilled in existing concrete walls corresponding to the horizontal rebar spacing...insert epoxy and rebar dowels (depth/diameter of hole and diameter/length of dowel should be specified by the Engineer - city/county inspector will likely want to see something from them about it). Dowels would then lap and be wired to new horizontal rebar. Note from engineer would be something like this: " #4 x 2' dowels at 12" o.c. at existing wall - imbed min. 4" into exist. concrete - secure with epoxy inserts"