If you know nothing about Rotorua, you'll know it smells like rotten eggs. And you'll probably know it's because of sulphur. But what's it doing to your house? Cira Olivier investigates.
Sulphur City has long been a nickname for Rotorua, a geothermal city renowned for its rotten egg smell.
Sulphur is a yellow solid which forms on and in the ground in geothermal areas, hydrogen sulphide (H2S) is the gas. Now, it is being blamed for causing damage to homes, heat pumps and jewellery.
Rotorua Property Maintenance owner Mike Quigley said he had noticed metal around houses in Rotorua in high-sulphur areas to rust far quicker than in other areas.
"Basically, it's like having a house on the beach."
But people were moving with the times, he said, and many households had switched from using metal around their property to now using plastic.
Independent research organisation, BRANZ, researched the impact of natural elements on different positions on a building.
BRANZ provided evidence-based advice on issues in building and construction in New Zealand, to industry and government.
The corrosion rates of the mild steel plate on a building and test rack were "vastly higher" in a geothermal area – in some cases by more than 10 times – than those found in rural and marine environments.
Property Inspect BOP building inspector Brendon Kenny said plumbing, timber and metal were at risk of discolouration and deterioration.
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"It eats through steel, even stainless steel fixings, it just rusts them all out," he said.
"Most of it's just general maintenance," he said, and while the corrosive effects would eventually ruin property, the same would be true about any other lack of maintenance.
He inspected homes in Tauranga as well and said the outdoor corrosion caused by H2S was similar to the seaspray in Mount Maunganui.
But because H2S was a gas, it could tarnish the inside of homes, which was not the case along the coast.
He said there was no way to prevent damage from the gas, "it's just Rotorua".
But people could protect their appliances and pipes with a corrosive resistant treatment, he said.
Tremains Rotorua sales manager Megan Davies said they had recently removed a heat pump in an Owhata home because the tubing had been destroyed.
"You wouldn't of noticed it if the heat pump was in place but because the tubing had been left exposed, it was very, very noticeable that it had corroded because of sulphur."
But this was not in a suburb deemed to be a "high sulphur" area.
The council's geothermal inspector, Peter Brownbridge, said there were a few areas which had generally higher levels of hydrogen sulphide.
Parts of Marguerita St, the area extending around the Pak'nSave intersection, Eruera St, Ngapuna, Wylie, Whakarewarewa and areas around the Government Gardens.
Gwendoline and Sophia streets and Motutara Point - also known as Sulphur Point - also had higher levels.
Brownbridge said parts of Lynmore can at times be affected by increased levels of airborne hydrogen sulphide.
He said Western Heights was the least affected due to wind conditions in Rotorua being mainly from the west.
Professionals McDowell Real Estate principal Steve Lovegrove said this was because sulphur "moved around".
He said the smell was more likely to influence someone who was from out of town than anything else.
But this was not reflected in sales, and areas like Victoria and Glenholme had higher prices due to the central location.
Atkinson and Donaldson Plumbing owner said copper was particularly susceptible to oxidising.
Rotorua Jewellers co-owner Jannine Pearce owned a store in Rotorua and Te Puke and said the jewellery in Rotorua needed to be cleaned up to six times more often than its sister store.
Pearce said silver, gold and base-metals tarnished and turned black, but the rate of tarnish slowed down when wearing the jewellery because of the natural oils on the skin.
When it was humid, temperatures were up or it rained, it seemed to get worse at a quicker rate, she said.
This was also reflected in her jewellery cleaning sales and she said the stock needed to be replenished often.
Rotorua Lakes Council's manager of building services, planning and development solutions, Darrell Holder, said areas in the city that are not necessarily defined as a "hot spot" could bear the effects of hydrogen sulphide.
"Our advice would be for anyone building here to consider that when determining what materials and building methodology to use."
How to protect your home against H2S damage
• Like any environment, external factors impact the building and homes require maintenance and upkeep.
• Corrosive resistant coatings can be used to slow down the corrosion process.