There are no specific requirements for the sound insulation performance of external walls within national Building Regulations. Normally the acoustic performance of an external wall is only considered when a significant external noise source is present e.g. a building is being constructed near a busy road, rail line or airport. If this is the case, the ultimate performance of the external facade would be dictated by the level of prevailing ambient noise.
In the majority of cases, the window units and any trickle ventilators will be the dominant point of noise ingress into a building. A SIP, much like timber studwork solution, relies on the mass and continuity of plasterboard linings to provide the majority of the sound insulation performance.
If the sound insulation performance of the wall needs to be improved, the use of acoustic rated plasterboard in multiple layers is normal. An acoustic consultant would need to be involved to determine specification and performance requirements.