How to attach new framing to existing stucco wall?

I am adding a shed to the exterior of my house. I will be attaching the new framing roof ledger to the existing stucco with lag bolts. The floor of the shed will be a very stout concrete slab with J bolts to hold down the sill plates. My question is regarding where the new framed walls attach to the existing stucco house. Do they need to be bolted on as well, or will simply adding some really thick silicone caulking do the job? If they need to be anchored down, what if the existing house studs aren't in line with the new framing?