wetlands, has been sinking at a rate of 2 millimeters a year for the last three decades. that may also have impacted the building structurally. ( alarms ) reporter: the town of surfside requires multi-family buildings like this 136-unit property to be re-certified every 40 years. the process involves electrical and structural inspections of the foundation, beams, columns, slabs, and the roof, where work was happening. those inspections were underwayk for the building, but had not yet been completed. buildings don t collapse, especially not like this without any reason or indication or anything like that. reporter: sinisa kolar, a structural engineer, was in the building a year ago. based on the videos he s seen, kolar suspects multiplele failures. most likely columns or some load-bearing beams that caused a first, local collapse, based on the videos, is it some form of cracking or something that