I am building an addition onto the end of my house. The basement walls are poured eco-block and have been back-filled to within about 8″ of the top. The backfilled area extends about 4 feet out from the house. A floor truss lays along the top of that wall.
I want to pour a concrete slab 4″ x 15ft x 19ft with a finished surface at about the same height as the top of the poured wall. I think I have to connect the slab to the existing wall (and possibly strengthen it over the fill area) because of the backfill under it.
Can anyone recommend a way to do this properly ?
Thanks, Joe, HBI
Replies
Form up the slab with trex or some other synthetic lumber (they won't rot lke redwood or pressure treated). Form it so there will be 5' squares (they won't crack no steel needed). Install lags, screws, keyway or rabbit into the side of the forms (it will stop deferential settling. Slope away from the house. Soak the backfill to compact more or expand if expansive soil. Cover the tops of the forms with plastic (it will keep them clean)
Okay, I think I understand, but want to clarify : I leave the form boards in for good, correct ? I'll end up with 5ft squares with the form boards just showing at the surface? Do I need to place a form board along the existing wall and lag it to the wall ?Thanks, Joe, HBI
Lagging into the wall is easier than grinding a key into the wall. I wonder why there is not a whole lot of opinions 'bout my ideas? I do suggest strange things, but I try to insert logic to it.
>> I am building an addition onto the end of my house. The basement walls are poured eco-block and have been back-filled to within about 8" of the top. The backfilled area extends about 4 feet out from the house. A floor truss lays along the top of that wall. <<
What is existing and what is new? Please insert the words "exiting" and "new" into the above. I'm guessing all of the above is existing?
Also, what is the (proposed?) foundation of the new addition? Is it a slab on grade w/ stem walls, a monopour slab & footers, a basement or what?
Edited 10/8/2005 5:54 am ET by Matt
What you highlighted is existing, and he is wanting to pour a slab to match the top of the top of the ICF wall.
Your questions are germane, and need answers, before further recommendations.
Good points.
Dave
Yeah, sorry, have my head so wrapped in the project,,,,,,,,the basement eco-block walls are existing walls, the backfill has been in place for 18 months. Hoping to pour one time, a new slab and footers. (NOT to confuse the issue, but this new concrete pad at ground level will have a small 8x14ft Endless pool sitting on its 'outside' edge (away from the house and backfill area). I plan to use a 2ft high eco-block wall around the perimeter of the new pad to help insulate the pool area. I'll install a floor joist system over the slab to bring it up to the existing house floor level (to match the 2ft existing truss height). The top edge of the pool will end up about 18" above the finished floor of the addition. So, really, the part of the new slab that is over the 4ft backfill area will not be utilized at all...ie. the floor joists above will carry the weight of the floor, the new slab will carry the weight of the pool but only over virgin soil).My primary concern is how to attach the new slab to the existing concrete wall?....and I guess, how to 'beef up' the new slab area over the 4ft fill near the wall ?
Hopefully this all makes sense, Stay with me, THANKS,I can attach a photo if necessary,Joe HBI
Endless pool - is that one of those lap pools with the pumps in it where you where you swim against the current? Sounds like it could have a major cardiovascular health benefit...
So - you are going to do a monolithic pour slab on grade "pool room" which will then have a framed floor on top of it. Well, for starters, the footers for the mono pour slab have to go all the way down to undisturbed earth including in the area of the backfill. As far as attachment to the existing structure, I'd drill 3/4" holes in the sip wall probably at least 4" into the concrete and insert #6 rebar into the holes - probably 16" or maybe even 12" OC - epoxie in the holes would be the proper way to go, but you should probably check it's compatibility with the foam in the ICFs.
Any backfill inside the perimeter of the new foundation would have to be either compacted material or washed gravel. I wouldn't do a lot of compacting right up against the basement foundation though... BTW - I don't think we know where you live so we don't have an idea how deep the frost line is.
Even though you say small pool - I'm making a SWAG that it's at least 10k #s - maybe even 15k. That's a lot of weight as opposed to normal household loads. Heck - even a full sized car only ways around 4k#s. How many gallons will the pool hold? Based on that I'd run the rod that is pinned into the existing foundation all the way out into the slab, and probably even run some rod the other way every 24". Use at least 3500 PSI concrete and maybe go 5" or 6" thick. You may want to cut back some to save $, but the way I recommended would be foolproof. The pinning into the existing house, and running the rebar all the way out isn't negotiable though. Not so much because you need a lot of strength there, but more because you won't have good (and even) support for the slab and you don't want the slab to move as it will likely crack big time right where the backfill ends. It's a good thing the pool doesn't have to go over the backfill area.
Or - here is a totally different approach: dig footers to undisturbed earth and pour. Then build stem walls up to the height of the existing foundation. Provide a lip inside the foundation to receive the concrete. The difference is that you only pour concrete under the portion of the pool room that is actually going to get the pool. Make sure the substrate under the concrete area is really good. Go ahead with the rebar and somewhat thicker/stronger concrete. Build the walls and floor system as you had previously planned - the floor system being supported by the stem walls. Could run into some engineering problems with support of the wood floor though...
Also, I'm not so sure about how much value the ICF kneewall would really add.
Come to think of it, this whole thing should be engineered anyway....
OK.....I have decided to have an engineer take a look at it....I bet it will be built close to the recommendations you gave me, but the building dept here will probably want an engineering involved anyway. I like the idea of running the slab all the way to the wall still, because it keeps everything tied together as one better....FYI: The endless pool is a current pool, my wife uses it for a workout nearly everyday, I use it mostly as an easy swim/stretching excercise after work and on weekends to loosen up. I know it saves us medical downtime. The thing is very well designed and constructed.....we bought it instead of a new car when we moved here (it gets better mileage). You can unbolt it and take it with you if you move. It ain't cheap.
It does weigh about 20K lbs or approx 178 lb/sqft when filled. We are in Western NC so the earth here is the 'Georgia red clay' with some rock.Anyway, you know how it goes...I was hoping for a 'simple fix' for this project, but the combination of the backfill and the pool weight nearby does make it tricky...I don't need to cause foundation problems or other shifting.Thanks for all your time and help, I appreciate it....this forum does work,Cheers! Joe HBI