New York City isn’t quite ready for a timber tower, but Brooklyn is about to take a crack at low-rise office and retail buildings made of wood. Flank, an architecture and development firm, is building two timber-filled commercial buildings at 320 and 360 Wythe Avenue in South Williamsburg. The firm is billing the projects as the first wooden structures to be built in the city in nearly a century. …Current city rules only allow wooden buildings of up to six stories tall. That’s not a problem for Flank’s 360 and 320 Wythe, which will respectively rise five and two stories. The projects are using a kind of mass timber, which is engineered wood that’s extremely dense — a feature that serves to strengthen the material and make it fire resistant. Flank’s using cross-laminated timber from Canada-based Nordic Structures.