SEOUL - A rooftop barbecue turned into a spat with his neighbour for Mr Alex Kim over noise that his daughter and her friends made jumping and running around.
"It was supposed to be a relaxing evening for everyone up on the roof last year, but our neighbour living right below came up to shush us and even called her housing agent to complain," said Mr Kim, 46, an entrepreneur who lives in a low-rise residential building in central Seoul, known as a "villa".
"So we complained back about her family keeping their stuff outside the house and blocking the fire exit stairway to the rooftop. We both got scolded by our landlord, who owns the whole building, and since then we haven't been able to enjoy the rooftop space."
Disputes between neighbours over "cheung-gan so-eum", or noise between the floors, have grown with the Covid-19 pandemic keeping more people at home since early last year.
Data released by the Korea Environment Corporation earlier in January showed that the number of complaints about noise from upstairs neighbours spiked to 42,250 last year, marking a 60.9 per cent increase and drawing concern over the social problems of high-rise living.
Stomping on the floor was the biggest issue (61 per cent), followed by dragging furniture, hammering, slamming doors and loud music.
About 60 per cent of South Korea's 50 million population live in multi-storey apartments and villas, but it was only from 2005 that the law required floors to be at least 21cm thick to allow adequate soundproofing. Most buildings constructed before that had floors with 13.5cm thickness.
The Internet is flooded with complaints about noise coming from upstairs.
One Twitter user said the noise made him want to "scream at the ceiling", while another said he was so angry that he drilled a hole in his wall for the sound, as retaliation.
Yet another user complained about children upstairs running and playing the piano in the early hours, adding that "they've been making noises for over an hour now so I started playing loud music aimed at the ceiling".
South Koreans are known to be sensitive towards noise from upstairs, with some experts warning that repeated exposure to such noises can lead to depression and insomnia.
In extreme cases, spats with neighbours have escalated into violence and even murder.
In 2016, a 33-year-old man living in Hanam city, 21km south east of Seoul, stabbed an elderly couple living above him, causing the woman's death. The man had complained about the noise when the couple had gatherings or grandchildren visiting on weekends, but it did not stop.
In 2017, a man in south-eastern port city Pohang was arrested for trying to strangle his neighbour while they were bickering about noise, while another in the south-western city of Gwangju was detained for destroying his neighbour's car because of a noise dispute.
More recently though, "cheung-gan so-eum bok-su", or revenge for noise between floors, has been trending online as people resort to buying gadgets such as woofer speakers to send noise upwards to torment noisy upstairs neighbours.
However, this can backfire.
Last August, a court in north-western port city Incheon city ordered a couple to pay 29.6 million won (S$35,000) compensation to their upstairs neighbours for tormenting them with various noise-making tools.
Experts said more building regulations are needed to prevent such disputes. It was only in the last decade that building companies started to pay more attention to sound insulation for floors, such as replacing thin wood laminates with 25cm thick concrete slabs, or adding noise absorbing materials.
Meanwhile, a Floor Noise Management Centre was set up in 2012 under the Ministry of Environment to manage complaints about noisy neighbours. The centre also provides on-site counselling and helps to measure noise levels.
A representative from the centre told The Sunday Times that 70 per cent of the complaints are about loud footsteps and running, and they would advise callers to try to talk it out with their neighbours.
"The best way is for the two parties to come to a compromise, such as the neighbour above agreeing to wear slippers and the one below agreeing to observe the situation for a month or two," the representative said.
Complaints are also handled by the security department in apartment estates.
Housewife Lee Soo-kyung, 30, who lives in Seoul, said the security guard in her estate would make a public broadcast and ask the supposed noisy neighbour to keep volumes down.
"It is so stressful to have to move like a mouse even in my own house," she told ST.
"I have to keep reminding my son not to run around and just play on the play mat because I don't want to become the next one to get shamed publicly."