It has been more than a week since a multistory residential building collapsed in Istanbul's Kartal district. The news and with it the debate on risky residential buildings have continued to dominate the headlines in Turkey.

Twenty-one people were killed when the Yeşilyurt apartment building was reduced to rubble on Feb. 6, and authorities have worked around the clock since to identify other buildings at risk of collapsing in the neighborhood.

An investigation is underway into the exact cause of the collapse but officials have announced that the building had three additional floors without building permit. Four people, including engineers who worked on the construction of the 27-year-old building, were detained yesterday for negligent homicide.

The collapse fueled a debate on the pace of urban renewal, while President Recep Tayyip Erdoğan, who visited the site of the collapse last week, said there were "lessons to be learned" from the disaster.

Urban renewal remains the only option, especially in Istanbul, the country's most populated city, which also happens to be under constant risk of experiencing a powerful earthquake.

A decade after the 1999 İzmit earthquake, which also hit nearby Kocaeli and Istanbul, killing tens of thousands of people, the government launched an ambitious urban transformation project. Urban transformation covers the demolition of buildings at high risk of collapse, particularly those built before the 1999 earthquake and those with illegal extensions, like the Yeşilyurt building.

Some 622,000 structures, from residential buildings to decrepit shops, were demolished to be replaced with new buildings across Turkey, and in Istanbul alone, 320,000 such places were razed by the government, with the owners provided new housing.

Experts, however, say more needs to be done as haphazard zoning plans in the past, combined with the use of cheap and potentially unsafe building material, put more structures under the risk of collapsing. In fact, seashells and inferior quality sand, not suitable for use in construction, were found in the rubble of the collapsed building in Kartal.

Meanwhile, more buildings are scheduled to be demolished in the neighborhood. The demolition drive wave may also expand to include other districts as more people have started reporting cracks in their old buildings after the recent collapse. Local authorities, on the other hand, have started inspecting structures that are under potential risk across the city.