Noise Control Project

Update on Noise Control Project

Stuart Hayman Oct 2011

From 2006/7 some metal roofs in Auckland were required to have plywood sarking installed underneath in high road traffic zones. This was in the belief that metal roofs without plywood would allow the noise transmitted into bedrooms through the roof to exceed the noise levels set by the Auckland City Council District Plan. Concrete tiles were assumed not to need sarking.

NZMRM thought this assumption to be technically incorrect and obviously made metal roofs uncompetitive. Some on the spot measurements showed the ply to be unnecessary for a particular location, but the situation continued and so we decided to take some action and investigate.

We engaged the University of Canterbury Engineering Department to plan a study. The project consisted of several sequential phases, each based on the previous phase’s outcomes.

The stages were:-

  1. Literature and direct enquiry survey worldwide of research that had been done;
  2. Acoustic laboratory work to determine the difference between different roof claddings;
  3. Laboratory assessment of a range of whole roof systems including variants in the ceiling linings;
  4. Field measurements of actual roof assemblies;
  5. Predictive modelling to allow design of roof/building systems to optimise noise attenuation for as range of external noise situations.

With assistance from TechNZ, NZMRM engaged the University to undertake first the literature survey (which appeared to show that little research had been done on this topic and none recently) and then Phases 2 and 3.

These showed that while there are some (unexpected) differences between actual roof claddings alone (i.e. not in a roof structure), in a complete roof structure with a ceiling and underlay, insulation etc, the make-up of the ceiling is at least as important as the roof cladding and that modifications to the ceiling structure were much more cost-effective and technically acceptable than installing plywood sarking directly under the roof cladding.

Sharing this research with other groups globally showed that in fact research is being done in this area and these contacts also showed the way towards field testing. The report on this work has been summarised and distributed to NZMRM members but a suitable report for Scope is in the pipeline, and will be published in an upcoming issue.

At this point we have been discussing the 4th phase, field testing, with the University, and have drafted a method. It is now pleasing to report that this phase and phase 5, computer modelling, have been taken up by Winstone Wallboards and Tasman Insulation, use of whose products GIB® plasterboard and Pink® Batts® were shown to be the most effective way to modify noise transmission through the roofing system.