SOAP Faults Vs Error codes

We were working on implementation of a web services layer (business services - SOAP ), this layer in turn will communicate with multiple web services which solves the same problem (e.g search).
While integrating multiple web services(SOAP, two options to communicate errors occur during the integration

1) SOAP Faults
- SOAP faults are used by some frameworks to represent business logic related error messages. This works as long as we do not have multiple SOAP services involved in a action.

2) Custom data structure / XML
- Define a XML response format for the web services API layer and return the respective the error code and error message defined.

We decided to use custom xml response structures to communicate any error occurred during processing /integration and let the SOAPFault communicates any actual soap faults.