Accessory Dwelling Units—those chic, space-maximizing havens taking over backyards and urban in-fill lots alike—are more than just add-ons. They’re statements of style, sustainability, and smart living. But what truly separates a fleeting prefab from a guest house with staying power? It comes down to the DNA of your build: materials.

So, if you’re dreaming of a granny flat that reads Architectural Digest, not makeshift shed, keep reading. Here’s the lowdown on the best materials powering today’s ADUs, from classic wood framing to eco-savvy bamboo, all built to handle real life with serious style.