medium density housing
Is it MDH/Mid-Rise or Residential?
Just because it looks the same doesn’t mean it is In the previous edition of Straight Up we covered the emergence of particularly Mid-Rise and Medium Density Housing (MDH) construction in NZ. In this article we’ll further explore the implications this likely has on Building Control and other construction related professions. One of the considerations already touched on in the April ‘19 Straight Up article was weathertightness. And indeed further work may be needed to better understand how cladding systems used for traditional residential construction can be applied to mid-rise and MDH developments. For example the overall settlement/shrinkage of taller buildings, particularly prevalent in taller timber buildings, must be designed for in the exterior cladding and associated junction details. Similarly with cladding performance during seismic events where movement in taller buildings differs substantially to the that of residential dwellings. This is an area BRANZ has identified as being of high importance and is researching to identify potential weak spots and factors that may limit the performance of different claddings designed for residential construction but used in medium density housing or midrise buildings. There are other relatively obvious impacts; clearly dwellings with multiple tenancies will require different noise and fire considerations to ensure tenancies remain ‘separated’. Consideration of acoustic performance in broad terms requires two feasible sound transmission paths to be consider in mid-rise and MDH buildings: • •
Fig 1. Shrinkage joins in cladding
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Airborne sound such as voices, music, or traffic noise for example is evaluated using the sound transmission class (STC) system. Impact sound transferred through the structure or its elements such as footsteps, moving furniture or ‘knocking’ plumbing is measured using the impact insulation class (IIC).
The STC rating ranges from poor sound control with little privacy at STC<30, to STC 40–50 where raised voices can be heard in adjacent tenancies, and STC >50 providing reasonable acoustic privacy. Occupants in mid-rise and MDH developments do expect a reasonable level of privacy and the ability to enjoy their own private space without undue influence of other
Clearly dwellings with multiple tenancies will require different noise and fire considerations to ensure tenancies remain ‘separated’. Consideration of acoustic performance in broad terms requires two feasible sound transmission paths to be consider in mid-rise and MDH buildings
straight up | WINTER 2019
