Location is very important in terms of defending your house. If you place your house on a landlocked location, you will be very easily raided, and it can be raided extremely easily. You need to be sure that you do not place your house near an outpost, which enemy players can teleport to once built during the War Phase.
When War Comes
During war, you should periodically warp to your house and check to make sure no one is destroying your walls. While you're in your home, your walls will regenerate health at a rate depending on its level. Also, you can use glory to instantly regenerate 250 HP of your house walls. Be sure you're well geared to kill any invaders!
If You Are Raided
Your walls will have holes in them if you have been raided, and they no longer regenerate. However, don't fret! The season will end soon, and all houses will be reset and you can start again. You can also keep using your Cottage Rooms and Farms. Your chests may also be empty if they raided them.
Why Defend If Rooms Still Work?
During war time, a team must destroy a certain amount of houses in order to begin attacking the kingdom defenses. Defending your house can slow down the enemy.