I have a 30′ x 50′ bi-level (also known as a raised ranch or split-foyer depending on what part of the country you are from). The basement garage is at grade with the doors on the 30′ wall. As you walk along the front and rear of the house, the elevation of the dirt reaches a height of about 2.5 to 3 feet. I want to create a walk-out basement with a patio which will require me to excavate 2.5 to 3.5 feet of dirt from the rear of the foundation wall.
My question is, will the excavation cause a problem with the footing depth as it may no longer be 42″ below the frost line here in New York? Secondly, with a grade level garage, is it likely that the house has a step footing, or is it more likely that the footing more likely to be 42″ deep on the garage side and continue at a constant depth around the parameter of the house?
My gut is telling me I need to get out the shovel and dig a test hole to determine footing depth.
Any help will be appreciated.
Replies
my gut and your gut are in complete guttural agreement
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You're probably right, but you may be able to create some version of a frost protected shallow footing in that particular area that would allow you to proceed. The IRC details it quite well, and you can also find details at pathnet.org.
Andy
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"Get off your dead #### and on your dying feet." Mom
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Andy, thanks.
I found a document called "A Builder’s Guide to Frost Protected Shallow Foundations," which details the application well.
The link is: http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf
It looks like I will be doing some hand digging and I also need to see if the building department will accept the construction method without an engineer signoff.
I’ll report back.
Best
Jamie
For heated buildings, FPSFs are detailed in the 2006 IRC. Assuming that's the governing code where you are, it should be a slam dunk.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
Perfect!
Yes, you can only tell by digging.
Around here, it is common to "bridge" the foundation wall from one footing section to another wherever the footing changes elevation, such as where a garage meets a house. Doesn't seem quite kosher to me but the inspectors accept it.