After Mrs. Wolowitz's death, Howard moved back into the house after he and Bernadette had moved out of their apartment and moved into the house which they decided to live in and are currently talking about renovating in "The Spock Resonance" (S9E7). Bernadette talks about how she thinks the "Jewish mother kisch theme" is depressing and she wants to change it. The rennovation has since been finished, giving a more modern theme.
In "The Fortification Implementation" (S8E20), a young man came to the house, Howard's half-brother Josh with whom he shares a father. Howard at first wanted him to leave when he couldn't stand the fact that his father has another family, but then they bonded over Howard being an astronaut and their similar personalities.
The Living Room
The living room is where the gang usually hangs out in the Wolowitz house. Many gatherings are in the living room, including when everybody came over to the house to watch Leonard and Penny's Wedding.
The kitchen is a place often showed in the Wolowitz house. Some memorable moments including in the episode The Positive Negative Reaction when Howard finds out that Bernadette is pregnant.
This room was Howard's bedroom from the time he was a baby to when he moved into Bernadette's apartment long after they were married. Stuart used it while taking care of Mrs. W until he moved out. It has since been renovated as the baby room for their daughter Hallie.
Other rooms that have been used in the show are the dining room, Mrs. W's bedroom which became Howard and Bernadette's, the crawl space under the dining room, the garage, the back porch and the front porch/front hallway.