What Foundation for Small Addition?
An existing building has a small addition (7′ x 7′, one story, with a shed roof). It’s kind of tacked on to an inside corner (on the exterior) of an old vacation house. It contains the pressure tank for the water well, the water heater, a water softening system’s tanks, a refrigerator and the breaker panel and electrical service entry for the house.
The addition is unsound, with a rotting 2:12 pitch roof and sitting on a seriously cracked concrete slab that I’m sure has no footings under the walls and lots of rainwater infiltration where the framed walls rest on the grade level slab.
There is not much mass in this little structure. If the frame is completely rebuilt to the same general dimensions what kind of foundation would be required? Is a thickened edge slab enough? Or do I have to put a footing down below the frost line with a frost wall up past grade?
It has to be kept from freezing in winter. It is insulated, but it won’t be part of the conditioned airspace (I think the gas fired water heater has been the only source of heat so far).
Oh yeah, It’s in southern Wisconsin. — Thanks
Edited 7/9/2004 12:43 am ET by freematt
Replies
I would excavate to below the frost line and pour a new footing and stemwall. If you don't, it seems to me your addition will be constantly subject to the movement of freezing/thawing ground beneath it.
Just because it's not conditioned space now doesn't mean it won't be later. Think about the use/potential use of that space over the next 100 years and build accordingly.
That might be a good application for a shallow frost protected foundation.
A google on that phrase will get lots of infomation.
Basically it is a shallow foundation, can be a slab with thickened edge with good drainage and insulation around the outter perrimitar and other the earth to keep it frost free.
Thanks for reminding me of the descriptive term," shallow frost protected foundation".
I thought I rememberd an FHB article about such a thing. I have most issues from #2 through current.
Searching the FHB website I found this reference:
Fine Homebuilding - February/March 1997 - #107
FROST-PROTECTED SHALLOW FOUNDATIONS
by Christopher R. Kendall
This innovative foundation system uses carefully placed insulation and a slab with integral footings instead of conventional deep frost walls
There are a thousand hacking at the branches of evil to one who is striking at the root. -- Henry David Thoreau
Edited 7/9/2004 12:11 pm ET by freematt