Since the Radley house in To Kill a Mockingbird is described as being "droopy and sick" and having a "drunken picket fence," the author implies the house is very run-down, not maintained very well, and has an air of unhealthiness about it. So many rumors have circulated about the Radleys that many people completely avoid walking by the house, and Jem and Scout run by it whenever they have to pass by.
The house is considered to be inhabited by a "malevolent phantom" - Boo Radley - who is described in monstrous terms according to the town gossip. This adds to the house's eeriness.
We know the house has a porch with stairs that Jem has to run up in order to touch the door on a dare. The front door is seldom opened, and the windows are covered with shutters. There are small patches of "cannas," a kind of flower, in the front yard that Mrs. Radley sometimes waters. There is a fence separating the house from the neighbors - it is on this fence that Jem gets his pants caught.
Most importanly, there is a large tree in front of the house. This tree is an important symbol in the book because it represents the point of contact between Boo Radley and the children. First, it is the place he leaves them gifts until his brother Nathan cements over the knot hole. Later, it is the place where he rescues the children from being killed by Mr. Ewell. Scout recognizes that it happened under the tree, as she later tells the sheriff, because the ground was cooler there (she was barefoot, so she could feel the coolness).