Zad
New Member
Posts:58
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| 12 Dec 2009 04:23 AM |
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Hello,
I am just about to start finishing the basement of a 42' by 32' building where I need every inch of height I can get. The building has an 8' ICF foundation and there is no slab and no history of water in the basement. I am curious to know if I can pour the slab so the finished elevation of the slab is the same as the top of the footing. I am aware of two issues: the possibility of increased risk for water leakage and the lack of internal support to prevent the wall bending inwardly from soil pressure. Are there other issues and are these issues absolute obstacles to pouring the slab this way? |
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Joseph Farella
New Member
Posts:57
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| 12 Dec 2009 07:07 AM |
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Have you asked your local building officials if the proposed placement of the floor is in contravention of the buiding code and the building permit that was issued for construction.?
I would spend the money and call in an engineer to assess your situation.
This would protect you against any future liability, if and when you choose to resell your building.
Most exterior foundation walls designs , regardless of its construction. depend on the concrete floor as part of its strength to withhold backfill.
Without a concrete floor in place, it would be difficult to determine if you have had any water penetration in the past, as there would be no evidence unless you happened to be standing there, when the water was coming in.
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Zad
New Member
Posts:58
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| 12 Dec 2009 08:22 AM |
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Thanks for the feedback,
I will definitely check with an engineer.
Regarding the water in the basement: I tee'd into the drain tile with a 4' pvc pipe and brought it up inside the basement so I have been able to check for water regularly and there has been none, even at the height of the spring run-off. That is not to say there never will be however we did have a lot of water last year and it was still dry.
The other thing I am pondering is that the ICF forms seem somewhat compressible and I am wondering if, under the soil load, the foam would compress some and allow inward movement even if there were a slab up against the foam above the elevation of the footing. |
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Joseph Farella
New Member
Posts:57
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| 12 Dec 2009 09:48 AM |
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I am assuming that you will be pouring your new concrete floor flush with the existing footings.
I have seen, where a product such as Leak -Bye( google their site) is placed prior to the placing of the concrete floor.
In your case, it would go behind the interior wall finish and will not have the concrete floor on top of it, as shown in the diagrams.
It can be hidden underneath what ever floor finish you are using if you adjust the floor height slightly.
I like to refer to it as out of site,out of mind.
I am assuming that you have granulars under the concrete floor that will take away any water that may come in.
If not I would place a 3" perferrated drainpipe along the inside perimeter footing and connect it to whatever it is you have in place to take away the water from the exterior drain pipe.
I do not believe that you should be concerned at all with any compressive foam issues.
First of all, it is the reinforcing steel , combined with the concrete that is allowing the wall to withstand the lateral soil pressures not the foam.
That is of course if the proper amount of reinforcement was placed in the concrete wall in the first place.
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Joseph Farella
New Member
Posts:57
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| 12 Dec 2009 10:21 AM |
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Just to clarify, the dimipled membrane will need to extend down alongside the footing in your case. It does not show this on the Leak-Bye website.
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Zad
New Member
Posts:58
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| 12 Dec 2009 11:57 AM |
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Hi Joseph,
Thanks for your time and input on this. I will definitely do the drainage around the perimeter of the slab and look into the product you mention.
I wasn't clear with my comment about the compressive strength of the foam. What I am questioning is if you place a slab in a standard way, on top of the footing and directly up against the foam block, do you still get some inward movement of the wall as the foam compresses slightly up against the edge of the slab.
Given your idea regarding drainage I guess my one remaining concern is whether or not the wall will move at the footing/foundation junction. The foundation and footing were well steeled and there is a keyhole in the footing. What do you think? |
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Joseph Farella
New Member
Posts:57
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| 12 Dec 2009 03:30 PM |
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During the placement of a typical 3 or 4 inch floor concrete floor there is not enough contact area to put enough pressure on the wall to compress the foam.
I have found that as the concrete floors cure, that it actually shrinks and pulls away from the wall.
An engineer will look at the height of the backfill agaisnt the wall, the type of the backfill material, the wall length of unsupported walls, the openings,etc. and will tell you if you are going to have any problems.
I personally would not go foward without his direction.
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Jerry D. Coombs, PE
Basic Member
Posts:138
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| 15 Dec 2009 06:24 PM |
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In general, there is no reason why you couldn't place the top of the slab at the top of the footing. There are, of course, the previosly mentioned items to address.
Often, the slab isn't needed to resist the soil pressure on the wall. It makes it easier, but it can be designed not to need it. Whether it is a problem depends on the floor soil, the backfill soil, and how thick your footing is. I could probably head you in the right direction, but you'd want to get your engineer to do the final calcs and documentation. If you'd like, you can contact me off line, or call, and I'll try to help.
If the bracing of the wall at the toe was relying on concrete to foam alone, it would compress the foam, but probably not enough to be a major concern. I haven run those numbers recently.
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Jerry D. Coombs, P.E.<br>Coombs Engineering, P.C.<br>
<br>You can have with quality; You can have it fast; You can have it cheap.
Pick any two. |
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ICFconstruction
Veteran Member
Posts:1324
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| 16 Dec 2009 05:52 AM |
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The concrete floor does not support an ICF wall from back-fill pressures, unless you remove the EPS every so often.
An engineer we work with specs to remove a 6" piece every 2'oc, or dowel the footing to the wall every 2'oc, or (what I do most often) a key way footing.
I also do not think your chance of water issues would be substantially increased. |
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| Brad Kvanbek - ICFconstruction.net |
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richm
Basic Member
Posts:107
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| 20 Dec 2009 10:25 AM |
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Zad and Jerry,
Would it be possible to add to the height of the wall by boring and installing rebar at the existing top of the wall and add the height you need with additional ICFs? I have done that in a horizontal add-on situation with normal poured walls but not for height. I'm sure it would have to be engineered. The wall at the top probably will not have to hold backfill...........would it work?
I have used additional courses of block to get more height on an existing block wall and on an existing poured wall. Just seems it could be done in your case.............Jerry, what do you think?
Rich Melius |
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jonr
Senior Member
Posts:5341
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| 20 Dec 2009 11:57 AM |
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How about a step in the basement - dig the center part down a little, but keep it up at footing level near the footings.
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Zad
New Member
Posts:58
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| 20 Dec 2009 05:29 PM |
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Ok guys,
I have spoken with several contractors and an engineer and there is consensus that pouring the slab at footing elevation is not a problem. I posted the following question on the radiant heating forum and have had zero responses so I am hoping one of you guys will be able to give feedback on the following questions. Thanks again, you have been helpful.
I am putting in radiant floor heat in a basement. The slab is going to be poured so that the finished elevation is the same as the top of the footing (to maximize ceiling height). If I insulate the perimeter of the slab so that I create a thermal break from the footing I am concerned that I will have a 4" strip around the perimeter of the floor (the uninsulated, unheated top face of the footing) that will be cool and condense water and potentially create mold or damage the flooring (I am planning on using cork). Specifically, I am going to stop the perimeter insulation about a half inch from the top of the footing elevation so that I can caulk the joint to prevent gas movement up into the building. If I use 1" EPS or XPS will there be enough heat from the slab moving through the insulation and/or the caulking to keep the footing warm enough so that moisture won't gather? If I use rebar doweled into the side of the footing every 24" oc will I risk damaging the footing from expansion/contraction? If not, would there be enough heat transfer through the rebar to keep the footing warm enough to prevent condensation? So many questions. And, if any of you reading this see other problems please voice them. Also, I live in a zone 2 climate, Southern BC Canada (same weather as Northern Montana) and the slab is about 7 feet underground.
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