The Braced Door is of average strength and lasts longer than the Wooden Door. First introduced in Snuggledell, Braced doors are not too durable, but they'll do in a pinch. They have almost twice the health of a Wooden Door, but half the health of an Iron Door, making them considerably worse than Iron. Once you have access to Iron Doors and Magic Doors, it's best to replace these.
Dungeon Keeper 2Edit
|"A reinforced Wooden Door, capable of sustaining moderate attacks."|
|— Dungeon Keeper 2 Manual|
Just like in Dungeon Keeper, Braced Doors are rated between Wooden and Iron doors. There are few reasons to used Braced Doors when Iron and Magic are available, unless you are strapped for cash, or the area is of very little significance, yet still needs a door.