Albert Barnes Commentary 1 Kings 16:18

"And it came to pass, when Zimri saw that the city was taken, that he went into the castle of the king`s house, and burnt the king`s house over him with fire, and died," — 1 Kings 16:18 (ASV)

The palace of the king’s house - This refers to the tower of the king’s house. It was a specific part of the palace—either the “harem” or, more likely, the keep or citadel, which was a tower stronger and taller than the rest of the palace.

Zimri’s desperate act has been repeated more than once. That the last king of Assyria, the Sardanapalus of the Greeks, destroyed himself in this way is almost the only “fact” we know about him.