Road Traffic Noise Acoustic Design Certificates:
Example of a building resource consent condition requiring a road traffic noise acoustic design certificate.
- All habitable rooms shall be protected from traffic noise from xyz Road (by ensuring they are designed and constructed to meet an indoor design sound level of 35dBA Leq(24hr) in bedrooms and 40dBA Leq (24hr) in all other habitable rooms. Where there are bedrooms and other habitable rooms with windows that can be opened, a positive supplementary source of fresh air ducted from outside shall be provided that shall achieve a minimum ventilation as specified in Section G4 – Ventilation of the New Zealand Building Code 2011.
- An acoustic design certificate, prepared by a suitably qualified and experienced person in building acoustics, shall be provided to Council’s Planning Guidance Manager (or nominee) at or before the time of application for building consent. The certificate shall show how the noise standards and ventilation requirement in the previous condition is able to be met.
Why is that particular consent condition there?
The usual reason for consent conditions of this type is – that if you want to build a house near a noisy road, then it has to be designed and built to be quiet enough for a reasonable person to sleep and live undisturbed in. So that the road owner’s ability to operate is better protected from lawsuits later from house occupiers who can’t sleep in their own homes because of road noise.
Some councils are better than others at planning/managing this downstream risk.
Councils can use this consent condition as an alternative to declining you permission to build on your site near a busy noisy road.
Further information from the NZTA is available here. https://www.nzta.govt.nz/assets/resources/effects-on-noise-sensitive-land/effects-on-noise-sensitive-land-use.pdf
What steps are involved in me doing one of these design and certification jobs for you?
1/ Create a computer model of the surrounding ground terrain. (for example hills, valleys etc)
2/ Draw a ‘road’ on that computer terrain model, using my environmental noise modelling software.
3/ Enter the characteristics of that ‘road’ into the noise computer model (traffic volumes, % heavy traffic, road surface type and other relevant parameters).
4/ Add any road barriers, bunds, site fences, other shielding houses etc that will affect the noise levels received at the new house.
5/ My environmental noise modelling software will then calculate the expected road noise levels at the new house site.
6/ I then pause and consider whether the software modelled numbers matches to what my tertiary qualifications, acoustics knowledge and 25 years of practical acoustics experience were expecting, assessing engineering risk carefully.
7/ If everything checks out, I specify the soundproofing that is required to meet the specified consent condition requirements, and write an acoustic design certificate.
Three worked examples follow:
1/ Subdivision with Laeq 24hr 55dB contour line.
2/ Smaller subdivision with modelled 2dB interval road noise contour lines.
3/ Moving noise sources (model power boats racing on a lake circuit) six minute races with wind direction corrected Laeq 15min 55dB noise contour line.
How do I soundproof a house cost-effectively and easily?
Typical soundproofing design tools that I’ll use include double layers of 10mm plasterboard, 6.38mm laminate/12mm airspace/5mm monolithic glazing that fits in standard glazing extrusions and simple mechanical flexi-duct ventilation in bedrooms near noisy roads.
What does an acoustic design certificate cost?
Please ring or email me for a price.
Ph 021 324 627 or 021 226 8784. bob@aenz.co.nz
I’m a one person business, working part-time from my home office.
So my pricing is pretty competitive compared to the bigger corporates – particularly for a simple road noise soundproofing design certificate in the Waikato/BOP.
Some of my building industry customers have stayed with me for 20 years now.
I can sometimes deliver design/inspection reports within 24 hours, – if you need an urgent turnaround.
I’m based on the Hamilton side of Tauranga – and I prefer small to medium sized residential and subdivision road traffic noise jobs in the Waikato/Bay of Plenty.
Road traffic noise further knowledge resources.
Road traffic noise is generated by vehicle engine noise, tyre vs road surface noise, by air turbulence noise and by other special exception cases (judder bars, rumble strips, potholes, drain covers, reckless drivers and crashes, % popularity of Harley Davidsons/Indian Motorcycles in the neighbourhood and so on).
The coarseness, hardness and porosity of road surfaces has a significant effect of levels of road traffic noise generated. https://www.nzta.govt.nz/assets/resources/road-surface-noise/docs/nzta-surfaces-noise-guide-v1.0.pdf.
Some councils plan and budget for installation of quieter road surfaces – as roads become busier. Some don’t.
Posted speed limits, daily traffic volumes, % heavy traffic, road elevation and slope, surrounding ground terrain, noise barriers and bunds, other reflecting house surfaces and distance from the road also all affect the noise levels that will be received at any proposed new house sites.
Road noise modelling is primarily done on a statistical basis (e.g averaged over 18 or 24hrs).
Calculated road traffic noise level ratings are usually given an L10 (18 hr) dBA noise level rating, (calculated over 18 hrs) or a Laeq (24hr) dB noise level rating, (calculated over 24 hrs).
Required noise levels inside new houses in New Zealand are usually specified as Laeq (24hr) 35/40dB in bedrooms and Laeq (24hr) 40dB in other spaces. Laeq translates loosely as an average noise level.
Bob Russell –
Director, Acoustics Certificates Ltd.
Post Graduate Diploma of Acoustics & Noise Control of the Institute of Acoustics UK, London (1991)
Additional Institute of Acoustics UK specialist papers in ‘Regulation and Assessment of Noise’ and ‘Environmental Noise’ (Merit passes, 2012)
Professional Grade Membership of the Institute of Acoustics UK
Auckland Council Building Warrant Number 1806 (Sole specialist building soundproofing warrant holder 2004 -2016)
Sponsor, www.regulatorynoise.nz
