Most cities have maximum lot coverage formulas. These have changed over the years. Attaching the garage may put you over the maximum lot coverage.
There are setback requirements from property lines which pretty much guarantee outside access to your backyard but I've never come across a specific requirement for providing access to a backyard. There is no requirement that you have to provide access to your backyard directly from the inside of your house at the back or side.
Garages have stricter fire resistance requirements (typically thicker sheet rock and fire resistant doors) if they are attached to a house.
There is a good chance you could attache your garage. Talk to the Santa Clara City building department. Links useful to Santa Clara City homeowners are at:
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To give you a broad answer: If what you're proposing is just making an interior hallway between the garage and house there shouldn't be any major planning objections from SC. As mentioned before, only knowing actual details about your property can fully answer your question. There are plenty of tricky details that require consideration for this kind of addition.
We are a construction company located in Santa Clara and can provide a design/build quote for you.
Whatever you do, always get a permit and do it right the first time. Once you sell your property the buyer & mortgage company will want to see proof of your final permit signatures.