In his classic book How Buildings Learn Stewart Brand highlights an idea by the British architect Frank Duffy: A building properly conceived is several layers of longevity. Duffy called these shearing layers. Each of the layers moves at a different timescale. Brand expanded on the idea, proposing six alliterative layers: Site— the physical location of a building only changes on a geological timescale. Structure— the building itself can last for centuries. Skin— the exterior surface gets a facelift or a new lick of paint every few decades. Services— the plumbing and wiring need to be updated every ten years or so. Space plan— the layout of walls and doors might change occasionally. Stuff— the arrangement of furniture in a room can change on a daily basis.