Well, we know by the book's title that houses are pretty important here. Heathcliff's entire revenge plot is tied up in gaining ownership of the two houses. Even though Wuthering Heights is a love story, it's the houses that Heathcliff is determined to get possession of; his plan is not to win Catherine back or steal her away from Edgar Linton.
Wuthering Heights and Thrushcross Grange are in many ways set in opposition to each another. (See "Doubles and Opposites," above) The Heights lacks hospitality and domestic comforts: chairs lurk, meats hang from the ceiling, and the kitchen, like unwelcome guests, is "forced to retreat altogether" (1.14). "Wuthering," as Lockwood tells us, is "descriptive of the atmospheric tumult to which its station is exposed in stormy weather" (1.12). Thrushcross Grange, on the other hand, represents refinement, class, cultivation, and propriety. It's the house Catherine aspires to socially, the house that will make her a "lady." The Heights sits exposed on a stormy hilltop, but the Grange is calm and protected down in the valley.
With all the crazy intermixing that goes on in the novel, though, these neat thematic oppositions start to get confused. When the novel opens we learn that Heathcliff owns both houses. But when Lockwood notices that the inscription over the doors reads "Hareton Earnshaw," we know that the family has lost the house; the laws of inheritance have been violated. (Remember, even though Heathcliff was taken in by Mr. Earnshaw, he was never named Heathcliff Earnshaw). Figuring out how this happened becomes one of our goals as a reader.