ICF and pier-and-beam (caisson)
Last Post 26 Feb 2009 03:51 PM by Chirp Frog. 5 Replies.
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charleybUser is Offline
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14 Feb 2009 11:14 PM
I'm in Colorado, and expansive soils at the site require my ICF house to be constructed on caissons (e.g., "pier and beam" construction).

Caissons are drilled and poured concrete, and the ICF walls will be placed on those caissons (and the basement floor will similarly be suspended on those caissons).

It sounds like a number of ICF manufacturers are unfamiliar with using their ICF products in this manner, although yes, it is done.  I'm looking for suggestions/pointers on ICF built on caissons.

I looked into InsulDeck, but I just can't afford $25/square foot (installed), including the rebar, concrete, shoring, and shipping from Florida to Colorado.  Similarly, Hambro and SpeedFloor look like great products, but it seems it would be much more cost effective for me to simply use steel I-beams across the caissons and pour a concrete pan floor.

This is a two-story plus walk-out basement, ICF to the roof.  We like stained/textured concrete flooring for the interior, so I'm thinking we'd have beam pockets in the ICF and pour all the floors the same way we do the basement floor.

Goals:  (1) floor load-bearing strength, (2) cost effective. 

What are your recommendations for the basement concrete floor on caissons, and the concrete floors for the main and second floor?  (What forms or products should I be using?)

I'm guessing roof will be SIPS because I just don't think I can afford a concrete roof (would have been nice).

--charley

buddenUser is Offline
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15 Feb 2009 05:45 PM

"I looked into InsulDeck, but I just can't afford $25/square foot (installed), including the rebar, concrete, shoring, and shipping from Florida to Colorado.  "

Look at LiteDeck; their home office is in South Sioux City, Ne. 


I'm neither a builder nor engineer, so can't comment on the rest of your note.  But a question ... will the caisson construction leave the under-deck open to weather?  In which case deck insulation is something to want. 
charleybUser is Offline
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15 Feb 2009 06:11 PM
Posted By budden on 02/15/2009 5:45 PM

, But a question ... will the caisson construction leave the under-deck open to weather?  In which case deck insulation is something to want. 

The caissons should merely replace the footing (and also happen to appear periodically under the slab inside the footing perimeter):  So, the back-fill against the basement walls will still happen, and the "void form" under the walls and basement floor will remain (an empty space, but buried).

In essence, the soil can go up-and-down with moisture swell, and not touch the basement floor (and that pocket below the basement is theoretically not exposed to the outside air).

As an aside, that *has* raised an interesting question regarding the insulative value of that void form under the concrete basement floor, and what other below-floor insulation is needed/desired (still thinking about that).
dmaceldUser is Offline
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15 Feb 2009 07:52 PM
Do you have to use caissons? In the New Orleans area buildings are built on top of pilings driven into the ground. I never looked close at how it was done but I know there are houses in Kenner where you can see daylight under the slab after the ground has dropped! It looked like the slab was just poured on top of the pilings. I was just wondering if pilings might be cheaper for you. Maybe you can find someone down in NOLA area to give you some tips.
Even a retired engineer can build a house successfully w/ GBT help!
Bruce FreyUser is Offline
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16 Feb 2009 06:22 PM

I am not crazy about the idea of using structural steel and metal deck near wet ground.

There are several possibilities for caissons (or piles) that come to mind. 
1.  The caissons are located at strategic places under bearing walls.  The caissons are connected by concrete beams and the slab and ICF walls are built on top of the beams.

2.  Instead of beams and a slab, a mat, or raft (really just a thicker slab) is used.  The caissons support the mat and walls are built on the mat.  Placement of the caissons is not limited to bearing wall locations.  This may let you use a flat slab instead of trying to form beams.
 
3. Build a concrete structure like 1, but use concrete columns instead of ICF and infill European style with brick or block, using insulation on the outside.  You could infill with SIPS (or even ICF) as well if it were cost effective.  Conventional concrete walls may be competitive in this situation, too, but I like the idea of a concrete frame with SIPS infill.

I think 1 and 3 are the most likely scenarios.  In 1, you still need to think about how to do the intermediate floors and the roof.  Bar joists and metal deck with concrete fill is a possibility.  if you wanted to use bar joists and metal deck for a flat roof, you do not necessarily need to use concrete.  Insulation can be fastened directly to the decking and the roofing installed over that.  In case 3, conventional concrete slabs and roof would be the way to go.

I think you will want to insulate the bottom of the beams and ground slab and have a vapor barrier.  You might consider using UNCOMPACTED fill under the slab.  This would permit you to build without lost or void formwork, have a vapor barrier and insulation, and it will likely have enough fluff in it to deal with soil swelling.  You will be using a structural slab in any case and and a bit of extra rebar would protect the slab from slight uplift.

Make sure you have a competent engineer with local knowledge.

Bruce

 

Chirp FrogUser is Offline
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26 Feb 2009 03:51 PM
Take a look at the Legalett.ca web site. Their solution to problem ground conditions may be of interest. We have used this product in place of caissons and grade beams. On two different projects the floors were done using colored and textured concrete. The slabs were then saw cut (scored) into patterns . This resulted in a fantastic finished floor. Stacking one block @ a time!
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