These documents explore inter-tenancy walls (ITWs) in medium-density housing, with a focus on New Zealand building standards and innovative solutions. They highlight the importance of ITWs for fire resistance and acoustic separation, while noting the Building Code's vagueness on the matter. The texts contrast this with the UK's more comprehensive regulations and discuss various construction methods, including timber and concrete systems. A new concrete ITW system called Stackcell is examined as a cost-effective, high-performance solution. Finally, an acoustic opinion assesses the sound insulation of the Stackcell system, demonstrating its compliance with the New Zealand Building Code's acoustic performance standards.