New Concrete over Existing Concrete?

[7 second chevelle]

Ok, here is my story. Last year I built a 32 x 40 garage in my back yard. Before ground could be broke, I had to have the area staked for 100 year flood zone. No problem, flood zone was staked, garage was built outside the 100 year flood area.

Garage was finished in November of 2010. Fast forward to Feb. 2011. Spring rains bring 2 feet of water covering my whole yard, including the garage! The picture shown below was before the water reached it's highest point. Well, now that the potential to flood again someday, I decided to have the garage raised above the flood waters potential.

The garage will be the only thing lifted. The concrete is staying where it's at. My question is, what can I do to fill the space between the old concrete and the new concrete that will be poured after the raising? Will I just have to bring in a bunch of stone and tamp, or can I do something with some kind of beams with a little fill?

Also, should some type of drains be put between the two floors, in case of flooding again, or will the residual water not be a problem?
Thanks for reading my dilemma, and any suggestions.

[LLWillysfan]

The simplest solution would be crushed stone as you mention. It's more expensive per cy but doesn't require compaction and is free draining.

Are you going to jack the building, add fill to raise the grade beyond the building limits and then place a new slab?

[7 second chevelle]

Originally Posted by LLWillysfan

Are you going to jack the building, add fill to raise the grade beyond the building limits and then place a new slab?

The plan is to have a house moving company raise the building above the flood water limit. Build a new foundation. Set the building back down. Then add fill on top of the existing concrete. Then pour a new floor.
The water is coming from a small creek to the right of the garage, and fills up my lot to the street on the far left of my property. The street is acting like a dam, and flooding my lot. The idea is to raise the floor level higher than the street level. The water should not get higher than the street. (It should flow over the road at that point)

[Bib Overalls]

Around here we use "builder's sand" for fill. I think I would drill a grid of holes in the existing slab. If water gets in it will eventually drain out.

[Edger]

Wonder if all the fill will drain out with the water if it floods again.

[LLWillysfan]

Originally Posted by 7 second chevelle

The plan is to have a house moving company raise the building above the flood water limit. Build a new foundation. Set the building back down. Then add fill on top of the existing concrete. Then pour a new floor.

Sounds like a good solution.

If the existing slab is haunched, you can easily form up a wall right on top of it. If isn't haunched, I'm not sure I'd use a 4" slab as the footer although I guess that's what holding up the building now. If your not going to bring the exterior grade up evenly with the inside, you'll definitely want to incorporate some kind of footer to resist overturning.

You should extend the new wall up 6-12" above the exterior grade to get your framing and siding up off the ground. If the extra width of wall on the inside will bother you, step the wall back to 6" above the slab.

As for fill materials, I think any of those mentioned would work fine. I'd probably put in a few PVC weeps to ensure the sub base could drain if water got in there.

Should be an interesting project. Please take pictures and keep us updated.

[LegacyIndustrial]

Hate to be a bummer but wouldn't this be a good time to call an engineer?
Your town may require stamped drawings on your design anyway.

[brownbagg]

yes we do it all the time. pour a foundation for the bldg, then have a couple feet dirt on top of the foundation for plumbing and electrical piping and then slab on top of the compacted soil.

[foleymech]

can the building be moved away from that low spot? Or is there not enough room on the lot.

[jhelrey]

It's a boat house!

[CARS]

Originally Posted by LegacyIndustrial

Hate to be a bummer but wouldn't this be a good time to call an engineer?
Your town may require stamped drawings on your design anyway.

I really like this idea. I see an elevated area to the left of the pic, your drive, and your garage under water. Beyond your garage looks like low land that is not developed.
If I was going to do something about this, I would want my garage moved to the other side of the drive if possible.

Just a thought. good luck!

[7 second chevelle]

Originally Posted by CARS

I see an elevated area to the left of the pic, your drive, and your garage under water. Beyond your garage looks like low land that is not developed.
If I was going to do something about this, I would want my garage moved to the other side of the drive if possible.

Just a thought. good luck!

The water that you don't see goes about 100 yards to the left of the garage and 75 to the right, to where the normally small creek is. I can't bring the garage forward, because my house is right there. My only option is up. My whole lot flooded except where my house is. It is built on high ground.
After I raise the garage I will have about 18 inches to fill. I was wondering if there is something that could be used to fill the space quickly, then put some 57 on top of that for the new slab? Thanks for the replies

[buening]

I would definitely recommend drains between the two slabs. If you get water in the aggregate fill and then it freezes, you will have one heckuva mess as it will expand and crack the top slab.

Depending on if you have the area sealed, you could pour some flowable fill in there. I don't know what that costs in your area though. It is basically a low strength cement mixture that hardens.