How much of the conflict in the story arises from an opposition between the central character and his or her environment?

The story’s title suggests two ways that “environment” can be understood here, both literally and metaphorically. The narrator refers to the building as the “melancholy house of Usher”; as a physical structure, it is gloomy and confining. The lineage of the Usher family, including their class position, is a social and cultural environment that influenced the siblings. Both the house and the family line finally come crashing down—an action foreshadowed by the description of the “fissure” in the house wall. Both of these would be in line with a central conflict of man versus environment, or nature versus nurture. However, since Roderick is losing the war against madness, a case could be made for man versus himself. At a bedrock level, good versus evil carries through the story.
Roderick Usher, the central character, takes what proves to be a fatal action when he mistakes his sister’s illness for her death. The narrator, concerned for Roderick’s mental health, has gone to visit him in his home. The narrator says the “mansion of gloom” has “vacant and eyelike windows,” and frequently compares the house’s atmosphere to Roderick’s melancholy. The rooms and halls are dark, and light enters only in "feeble gleams. Perhaps most important, the house contains a subterranean vault. Not only is there an actual vault, there is also a painting of it on the wall.
As local elites, the Ushers are separated from the “peasantry” by their social position and their isolation in their dreary mansion. The declines in Roderick’s mental condition and Madeline’s physical condition are also compared, as she undergoes "a gradual wasting away of the person" that resembles his looming madness. Roderick moans about the "constitutional and family evil" that afflicts them. The question here is whether incest has been practiced in earlier generations and by the two siblings. If so, genetic bases for their illnesses may be suggested, or the traumatic consequences of the children’s experiences of abuse could have contributed to their afflictions.
Raised and living in the creepy mansion, in a dysfunctional family that may see incest as normal, all throughout their lives, we could view Roderick as well as Madeline as being buried alive.