Frost Protected Shallow Footings In NE IA

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Old 05-20-2008, 12:06 AM   #1
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Frost Protected Shallow Footings In NE IA

As a contractor myself I realize that each area will produce it's own set of code compliance regulations...
That being said, I am finally able to begin construction on my Tim the TOOLMAN Taylor garage. Size will be 32 X 26 or 32 X 24, depending on my presentation to the administrative authority, to make a long story short, It is located in NE IA normal frost footing depth 42" (same as Fairbanks, AK) Have been looking into Frost protected shallow footings. This garage will have...Radiant in-floor heat as well as radiant snowmelt on the approach and an adjcent slab patio between the house and the garage and radiant snowmelt in a carport. Essentially 3 sides of of the exposed ground surface around the garage will be "Warm" in the winter.
I would like some WORST CASE SENARIOS AND some BEST CASE SENARIOS for using Frost Free Footings in an accessory building. This garage has a boiler that produces the HEAT for the IN-FLOOR as well as the SNOWMELT and the domestic HOT water used in the garage.
Domestic Hot includes a LAV and a H/C combination sillcock, I plan on installing a 1/2 bath W/C, Urinal, Lav.
In this area they are kind of behind the times regarding new building techniques, I would like to hear from others that have frost free footing experience, any tech data to add to my collection to present to the Powers above would be appreciated.
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Old 05-20-2008, 01:00 AM   #2
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Re: Frost Protected Shallow Footings In NE IA

Rule of thumb, Actually the code I followed was for every 12" you were above the frost line you need 1" of styrofoam and it must extend 1' from the foundation, 24" up, 2" of styrofoam, 2 feet from foundation and so on.


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Old 05-20-2008, 09:55 PM   #3
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Re: Frost Protected Shallow Footings In NE IA

Here's the deal-if you want a perimeter that won't crack up, then you need a 12"x12" perimeter with 1/2" rebar in it. If you want to insulate, then get someone who can trench 8" wide and have them trench your footings 42" deep. Rip 6" off some 2" polystyrene and put the 42" on the outside of your trench and form up the slab and pour it all at once as a monolithic slab, or use the 6" remaining strip and form up the inside of your footing and just pour the footing, then top it off with the slab.

Put a 1/2" rebar about a foot from the bottom, and another about a foot from the top. Put vertical rebar in and bend them down into the slab when you pour it.

This will use a bit less than 2x concrete as the 12"x12" perimeter, but you do have a frost footing. You don't need the polystyrene for this, but it will insulate your slab from outside cold. The need for insulation under the slab is another story.

Good luck finding a trencher who can go straight. Don't sweat it too much, just make your forms right and don't worry if the footings vary back and forth a bit underneath.

We can build an accessory building here and in Des Moines max 24 x 32 without footings or a thick perimeter. I don't have any qualms putting a framed building on a 12"x12" perimeter, but it's got to have footings for masonry walls.
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Old 08-05-2008, 12:18 AM   #4
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Re: Frost Protected Shallow Footings In NE IA

How can you talk about monolithic footings and not mention drainage? Neither of the above responses mentioned how the drain tile should be installed or the soil in the trench prepared before the pour. Perhaps I misunderstood the situation. The soil holds up the structure and the water if it freezes makes it expand. Tell me i'm wrong on this.
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