Flanking
Flanking is indirect sound transmission that bypasses a separating wall via junctions, ceilings, floors or service penetrations, causing NCC compliance failures in-situ.
Ask Chalkline about this →Flanking is the transmission of sound between adjoining dwellings via an indirect path that bypasses the separating wall itself. Instead of passing straight through the wall, sound travels around it: through the ceiling cavity above the wall, through connected floor slabs, via rigid bridging in a double-stud cavity, or through pipes and conduit that cross from one side to the other.
Flanking is the main reason separating walls that pass laboratory testing fail to meet the NCC Rw+Ctr 50 requirement when measured in-situ. Independent testing cited in the ABCB Sound Transmission and Insulation in Buildings Handbook (2022 edition) found roughly 65% of in-situ walls fall short of the NCC minimum, nearly always due to flanking rather than any failure of the wall panel itself.
Under NCC 2022 Housing Provisions Part 10.7, the code addresses the main flanking routes by requiring the separating wall to extend to the underside of the roof (not stop at ceiling level), requiring discontinuous construction where wet areas adjoin habitable rooms, and prohibiting service penetrations that bridge both stud rows.
Also known as: flanking transmission, flanking path.
Category: Compliance & approvals.
Related
- NCC sound insulation, Part H4P6 and Part 10.7 requirements