IFC stem wall concern
Last Post 26 May 2015 10:11 AM by FBBP. 4 Replies.
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gosolarUser is Offline
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23 May 2015 03:54 PM
Met the surveyor at the site to mark up the slab's 4 corners.

I thought by my line of sight it was off a bit lower but now find the following.

I'll call the corners by compass heading

SW elevation 0

SE down 6'

NE down 10'

NW down 5'

My first thought was grade out the area dropping 2' on the SW corner thus decreasing all other differences by 2'

I need to have a slab because this is a passive build.

My concern is that NE corner being 8' the backfill and compacting that much soil in that corner (about a 15x15 slope area) and having issues settling or IFC problems later on .

Any suggestions how to accomplish this.

It's needs the height for the views so just leveling all won't work.


arkie6User is Offline
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23 May 2015 04:53 PM
For one thing, don't use soil for backfill. Use non-expansive fill such as gravel, rock crusher dust, or fill sand. I used fill sand for my garage slab that has ~8' of back fill on one end. That was several years ago and no issues or cracks to date. Back fill in small lifts, 6"-12" and compact after every lift. With the fill sand, I used a vibrating plate compactor. It was relatively inexpensive to rent and easy to use.

If your foundation wall is ICF and the slab will just be butting up to the side of it, there are a couple of other measures you can take to insure the slab doesn't shift near the wall. For my garage slab that abutted the ICF wall of my home, I cut 3' long pieces of #4 rebar, put a 6" hook on one end, and stuck one of these every 16" into my ICF wall at the level where my garage slab would be. This left ~2' of rebar sticking into the garage slab. I tied the garage slab perimeter rebar and 6x6 wire mesh to these 2' stubs of rebar. Also, on the slab side of the ICF wall, I stacked 8" concrete blocks on the footing and against the ICF wall up to where the bottom of slab would be. I put one of these block columns ever 4' where the slab met the ICF wall. When we poured the garage slab, we filled the block cores first.
gosolarUser is Offline
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23 May 2015 05:26 PM
Posted By arkie6 on 23 May 2015 04:53 PM
  Also, on the slab side of the ICF wall, I stacked 8" concrete blocks on the footing and against the ICF wall up to where the bottom of slab would be. I put one of these block columns ever 4' where the slab met the ICF wall. When we poured the garage slab, we filled the block cores first.
Why the piers in the inside of the slab wall not outside of the wall?

I know not soil just a typo. So not issues on the height of the wall

Where the slab meets the wall I was going to cut away about 5-6" of the inside IFC block height, add rebar like you suggest, but the slab will join the IFC wall at the top directly.

The outer core of the IFC should give me the insulation I need on the edge of the slab

jonrUser is Offline
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24 May 2015 07:45 PM
Consider that filling a 25x25 garage to an average 4' level is around 100 cubic yards of fill. This might encourage you to dig a little deeper on that SW corner.

I've been told that pea gravel is self compacting, but I don't know if this is true enough for all uses.

If a slab is partially supported by fill and partially supported by piers or rebar into a wall, I'd be concerned about this encouraging cracking. It might settle more when sitting on just fill, but it should be even (ie, no cracking).



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26 May 2015 10:11 AM
If op uses a self consolidating fill like pea stone or gravel, what stops it from sliding down the hill?

If using good clays or clay loam soils, good compaction (heavy commercial vibrating knobby wheeled compactor) will get the results required.

Is concerned about the inside fill, install a brick ledge just below the garage slab height and insert rebar into it to tie into the slab later. And yes use piers as per Arkie but don't use mesh. Minimum #5 bar @ 16" o/c.
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