Mass timber structural systems are increasingly used in the design of low and mid-rise buildings. One of the primary motivators for using mass timber structures is their low embodied carbon emissions (EC), which reduces a building’s carbon footprint. Despite this advantage, a criticism of mass timber structures in multi-story buildings is often poor air-borne and impact sound insulation. In response, this paper studies common mass timber floor assemblies for their EC and sound insulation performance. EC data is used along with previous experimental acoustic data to evaluate how acoustic insulation affects the sustainability of mass timber floors. This study found that there is no clear relationship between EC and acoustic insulation; while high-EC assemblies exist, there are many low-EC assemblies at all levels of acoustic insulation. Trade-offs instead occur in the types of assemblies that can achieve performance goals and their depth or visible finish.While other factors such as cost or structural requirements may control assembly selection, designers seeking to reduce EC should consider room design needs and select acoustic insulation strategies with favorable EC-to-acoustic insulation ratios.