The appraised value of a 2 car garage (vs. no garage) could depend on the neighborhood, the value of the home and the materials used to build it. If it's a custom home, with more expensive materials, in an area of nicer custom homes, the appraiser would take this into consideration. Also, different appraiser's will give different values.
With building cost down due to the recession, you could probably get a contractor to build a two-car structure (around 380 square feet,) for about $35 to $45 a square foot or for $13,300 to $17,100.
If it's a larger 2 car garage with plenty of room for two vehicles with easy in and out access, plus some extra work space, lighting, and storage, the size could grow to 800-850 square feet, at $29,000 to $38,000 or more. If someone is doing custom building with quality materials the cost to build it could rise to $55 a square foot, or $21,000 for a two-car garage and up to $45,000 for the larger version. These are of course for "new builds", and the appraiser would probably be comparing homes of a similar age to the one without the garage.
On an appraisal, if the house was a fixer, with inexpensive materials, that would effect the value of the garage. I have heard an older (non custom) garage might appraise at around $10,000, compared to no garage. Maybe less. If it's on a more expensive, custom home in a good neighborhood, who knows, maybe $15,000 - $20,000? There are a lot of variables.
Orangevale is so diverse. There are newer homes near older homes. Large estates are being built on those large lots. It's a nice place to live.