Foundation evaluation for 2nd floor addition

[slotownman]

In planning for a second floor addition over the garage and rear section of my home we have found two problems that require engineering solutions to over come the foundation's limitations.
Background: This home is located in South Lake Tahoe, Ca. Live weight,snow load and wind sheir conditions must be accounted for. The living are of the home (circa 1965) is built on a continous foundation around the parimitar, which is 18-20" deep, 18" wide, with a 6.5" stem wall. The subflooring is supporte by piers arrainged in a 4x6' grid. The garage is attached to the house but it's built on a 10" slab, with out a foundation supporting it's parimitar.
My questions are:
1). Can a foundation be poured under the edges of the grarage and the slabe attached to the foundation? if so how.
2). What can be done to the stem wall or foundation to upgrade it's capacity for the weight of a second floor. (I know this is a difficult questions which requires more input as to the beam and framing structure, materails, and of course the soil composition that foundation is sitting on and a few more things Im sure I have not considered.

 

[Focht3]

Don't forget earthquake forces! Whatever you do to the garage foundation, it needs to be mechanically attached to the existing foundation. And adding a second story dramatically affects the behavior of the structures in a seismic event.

I've been to Lake Tahoe - beautiful place. There's also a good bit of relief, so the effect of ground slope also has to be accounted for. My suggestion? Hire a good structural engineer - considering the price of real estate in your area, the natural forces you must deal with, and the complexity of your problem, you need professional help.

 

[dik]

In addition to the above, if you are constructing higher than the surrounding building, you can have snow accumulation. In addition, when changing the loading regime for an existing building, be prepared for some differential movement of the existing; this may cause some cracking of interior partitions.

 

[slotownman]

Thank you guys, for the reality check. Your both right about all potential conditions I'm going to encounter in this adventure. I have allready made the decision to hire a structural Eng from the area, as I have done my home work and found this to be much more complicated than I had orginially anticipated. I believe in doing this right the first time and with this type of project that all you get is one time. Thanks for the advice.
Kurt

 

[CadAndy]

I see you already hired an Engineer to help and here's
what I read when I designed foundations for hotels.

Piles are an excellent structural source if your soil
absorbes more than 4%. If I can remember correctly.

Anything over 20 feet requires a 10 inch stem and
at least a 24 inch footing. Its suppose to be 2 times
the stem A/2. 'A' being the stem.

Most of the books I read were written in the 60's
So I am assuming technology has changed alot since
than. But At least its a guideline.