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Old 08-15-2009, 08:26 PM   #1
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Extend Footing Depth


My building inspector will be getting back to me, but I've discovered that our attached garage (which we would like to convert) only has footing that go 16" or so. Iowa frost depth is 42".

1.) Is there any chance that a building inspector would allow a conversion to take place on this sort of footing?

2.) If not, Is there anyway possible to extend the depth of the footer? What kind of a job is this?
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Old 08-15-2009, 09:26 PM   #2
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You probably aren't going to be able to leave it as-is and build habitable space on it, or use the existing space as habitable space.

Making the footings deeper isn't really an option.

I'd give some thought to proposing insulating the exterior side of the footings and/or foundation wall with 3" foam board. They might be willing to give that a shot.

How did the inspector know the footing depth of the existing building???
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Old 08-15-2009, 09:34 PM   #3
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Worth a shot -

Frost protected shallow foundations - 14" VS 48" normal - page 5 as an example
Depth depends upon area/frost depth I guess

http://www.toolbase.org/PDF/DesignGu...dFPSFguide.pdf



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Old 08-15-2009, 10:39 PM   #4
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Interesting read, thanks Dave. Much more detail than the one I've been using: http://www.oikos.com/esb/43/foundations.html
Sorry, cibula 11, probably cheaper to demo the 16" and re-pour, unless they buy it insulated.
Be safe, G
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Old 08-16-2009, 12:29 PM   #5
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Quote:
Originally Posted by thekctermite View Post

How did the inspector know the footing depth of the existing building???

The inspector doesn't know the depth of the footer (yet). I was curious so I dug down and found it. I guess I've been wondering if I should say anything or if I should keep my mouth shut. He is suppose to be getting back to me on what things I need to have so I can convert the space.
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Old 08-16-2009, 04:11 PM   #6
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Keeping your mouth shut could end up hurting you. Maybe or maybe not. 3' of frost protection is pretty common, but northern states often require more. In reality, here in KS our frost depth requirement is 36". In the coldest winters we've had we rarely have more than 6 or 8" of actual frozen soil. In colder states it is of course deeper. If your footing's soil freezes you're destined for problems.
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Old 08-16-2009, 05:36 PM   #7
 
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in sw mn code last time i checked is also 42" but i have also see water lines buried at 6' freeze
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Old 08-16-2009, 05:40 PM   #8
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The garage has existed at its current location for over 70 years with no structural cracking whatsoever. I know what code will say, but do I bury myself by mentioning that I already know the current depth?
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Old 08-17-2009, 05:06 PM   #9
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Quote:
I know what code will say, but do I bury myself by mentioning that I already know the current depth?
Ayuh,....Only if Asked.....

I like the Frost Curtain Idea,... I put a small 1 on 1 of my houses last year,...
No Frozen Pipes,... So I guess it Works......
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Old 08-17-2009, 05:19 PM   #10
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The subject of frost heave is actually a lot more complex than is generally realized. Frost heave refers to lifting of a slab due to freezing of moisture in the soil below the slab. This occurs because water expands when it freezes (but everyone knows this). However, actual frost heave requires more than moisture in the soil and freezing ground temperatures.

In order for frost heave to occur, the moisture in the soil must be "free" moisture, meaning it is not chemically bound to the soil. For example, clay typically has a large amount of moisture chemically bound to the clay molecules, however that water is not free, and will not freeze. Coarse sand and gravel may have free water in them, however they typically do not produce frost heave because the ice expands horizontally rather than vertically underneath a slab; no vertical expansion, no frost heave.

The soils with the greatest problem are fine sands and silts. Both of these materials will hold free moisture, which will heave if the soil freezes. If your foundation is built on clay, coarse sand or gravel, it is not likely to frost heave, regardless of how deep the freeze line is in a given winter. In that case, placing the foundation deeper is not important, except to meet code, and you may be able to get a variance from the building inspector if you get a sign off from an engineer.

On the other hand, if your foundation is built on fine sand or silt, it will almost certainly heave if the soil is saturated or near saturated prior to freezeup. From your description, there has been no problem of heave in 70 years, so it is likely that you are built over soils not subject to heave, and you may well be able to get approval from the building inspector if you produce a letter from an engineer pointing out the relevant facts.
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Old 08-18-2009, 02:59 PM   #11
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Here is a response from my inspector:

I just reviewed the Residential Code again and basically the following would be necessary changes to create a bedroom out of your attached garage space:

Smoke detectors
Insulation
Egress Window
Ductwork for HVAC
Additional Outlets
Of course a submitted plan and permit


This is all that appears to be required for the remodel into a bedroom, if you would like to set up an preinspection we would be glad to come out and see if there are any other obstacles I didn't think of.

If you have any questions or concerns feel free to call me.



So I suppose I'll have him come and out and evaluate the garage. If he says its a go, then I'll go with it. If nothing comes up about a footing, then oh well.
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