Interestingly, the house of + surname is a phrase often used to represent a prominent family, such as The House of Windsor which indicates the royal family of England. Also, the "house of --" can mean the mansion belonging the family. Poe's double entendre, "The House of Usher," then, can denote either the mansion or the last members of the Usher family. Thus, the one reflects the other. As Roderick becomes more and more disturbed over the death of his sister, he wanders through the house. The narrator, who cannot sleep, notices the atmosphere of dread around him in the house: "a faintly luminous and distinctly visible gaseous exhalation which hung about and enshrouded the mansion." Also, the narrator notices a fissure in the wall that previously has not existed. And, after Roderick has been caught in the final death agonies of his sister, this earlier almost indiscernible fissure rapidly widens and with the "mighty walls rushing asunder," the House of Usher crumbles to the ground, mirroring the death of Roderick Usher.
Whether it is the catacombs in "The Cask of Amontillado" that reflect Montresor's disturbed and twisted character of the House of Usher, whose dilapidation reflects the own mental instability of its owner, Roderick Usher, Poe always uses setting to great effect in his gothic, spine-chilling tales of horror. Consider what we are told about the House of Usher:
Its principal feature seemed to be that of an excessive antiquity. the discoloration of ages had been great. Minute fungi overspread the whole exterior, hanging in a fine tangled web-work from the eaves. Yet all this was apart from any extraordinary dilapidation. No portion of the masonry had fallen; and there appeared to be a wild inconsistency between its still perfect adaptation of parts, and the crumbling condition of the individual stones. In this there was much that reminded me of the specious totality of old woodwork which has rotted for long years in some neglected vault, with no disturbance from the breath of the external air.
Note the overall emphasis on rottenness and decay. The setting of course is a symbol that could be said to represent the madness and mental disturbance at the heart of the owner of the house. At first glance it appears to be of sound quality, but closer examination reveals issues that could indicate serious structural problems. Remember, the narrator has journeyed here, not out of choice, but because Roderick Usher, his childhood friend, has written to him to come and be with him as he is suffering from a "nervous agitation" and a "mental disorder". How mentally disturbed he is will only be revealed at the end of the story...