Why is acoustic design important near busy roads?

Road traffic noise pollution is generally one of New Zealand’s less considered problems. But exposure to ongoing traffic noise has definite physical and psychological effects on individuals and communities. In plain language: if human beings don’t get sufficient periods of deep, undisturbed sleep because of road traffic noise, their and society’s decision-making abilities degrade. 

As New Zealand’s population increases, there is more traffic, and there is more traffic noise. Where people used to have quiet environments at home, enabling sufficient deep, undisturbed sleep, that is sometimes no longer possible near now busier suburban arterial roads.

Traffic noise can make a residential home unusable, forcing homeowners to seek action against the road owner. Councils and other road owners are aware of this potential problem and therefore require that, if a new house is to be built near a busy road, the proposed new house be soundproofed and engineer certified as quiet enough to sleep in.

How does the road traffic noise design process work?

When I’m asked to do a road traffic noise design for a proposed new house, I first create a computer model of the surrounding area. This model assists me in assessing how loud the road noise will be at the new house site. From there, I certify what soundproofing is required for the new house.

To create a computer model and to make a traffic noise assessment, I use the road traffic data (road surface type, speed, percentage of heavy traffic, road width, road slope and road elevation) as well as my specialist library of ground terrain data, other buildings and barriers. I also use my specialist noise modelling software, my on-the-ground knowledge of the Waikato and Bay of Plenty regions, and my experience and professional qualifications in acoustical engineering.

To do a soundproofing design that is covered by insurance, I draw on my formal acoustics and noise control engineering qualification and my 12 years of experience as Auckland Council’s sole specialist highrise-building soundproofing inspector (2004 – 2016).

What building modifications are typically required?

Typically, if I need to increase the soundproofing specification of a facade wall, I’ll add an extra layer of interior plasterboard. It’s easy to understand for builders and designers, easy to implement on-site, and comparatively cheap.

If I need to increase the soundproofing specification of a ceiling/roof interface, I’ll specify an extra layer of interior plasterboard. It’s easy to understand for builders and designers, easy to implement on-site, and comparatively cheap.

Standard modern exterior double glazing will achieve about STC 30. If I need to increase the soundproofing specification of some windows, I’ll typically specify 6.38mm/12mm airspace/5mm monolithic glazing (STC 38). This glazing combination still fits in a standard window frame extrusion and is comparatively cheap.

Mechanical ventilation may need to be specified if a room’s windows need to be kept closed for soundproofing.

If required, typically, this is implemented using a light in-line fan in the ceiling void with 2-3m of flexiduct upstream and downstream of the fan. The fan brings fresh air into the required room from outside, from the quiet side of the building. Sometimes a separate ventilation engineer’s certificate will be required by council. A rough but useful rule of thumb is that you need 4 or more air changes per hour to the targeted room. For example, a 30m cubic metre room will need a fan that pumps 120 cubic metres or more of air per hour.

What does a road noise soundproofing acoustic design certificate for a new residential building typically cost?

Give me a call, tell me about your building. Then I’ll competitively quote the cost of the report for you on the phone. But a simple road noise building soundproofing design certificate is typically around $1,000 + GST.

How long does it typically take to get a road noise acoustic design certificate done?

I can often turn road noise soundproofing design reports around in 2-3 days. Sometimes it’s even quicker if you really need it urgently.

When are road noise soundproofing design certificates normally required?

When a new house is proposed near a busy road. As one example, within 80m of a road with a daily traffic count higher than, say, 2,000 vehicles per day.

What additional information does the client need to supply?

Items that I need from the client are copies of the building plans and preferably copies of the resource consent condition or RFI.