The Three safe houses?

[randale]

To clarify exactly what houses are vulnerable to AoE attacks under the foundation, it is all housing types with a foundation edge that is the same as those found on a tower. This means that towers, castles, and keep can have this done to them

Ok, so now I understand that's only those three houses. But, saying "foundation edge" is somewhat misleading as ALL of the player houses on the shard have that foundation edge, every single one.