façade = The face or front of a building towards a street or other open place, esp. the principal front. (OED) ARCHITECTURE visible surface: the face of a building, especially the principal or front face showing its most prominent architectural features (Encarta)
Δεν ξέρω αν λένε active οι αρχιτέκτονες, αλλά αφού έχεις και «δευτερεύον» παρακάτω, νομίζω ότι το principal ταιριάζει.