Describe the setting

From the text:

The setting is the yard which fronts the only entrance to the Maxson household, an ancient two-story brick house set back off a small alley in a big-city neighborhood. The entrance to the house is gained by two or three steps leading to a wooden porch badly in need of paint. A relatively recent addition to the house and running its full width, the porch lacks congruence. It is a sturdy porch with a flat roof. One or two chairs of dubious value sit at one end where the kitchen window opens onto the porch. An old-fashioned icebox stands silent guard at the opposite end. The yard is a small dirt yard, partially fenced, except for the last scene, with a wooden sawhorse, a pile of lumber, and other fence-building equipment set off to the side. Opposite is a tree from which hangs a ball made of rags. A baseball bat leans against the tree. Two oil drums serve as garbage receptacles and sit near the house at right to complete the setting.

what does the porch lacks congruence mean?