Does "Defense Buildings" bonus cover fortifications?

[MSH]

If it does - then extra strong walls could be nice. Otherwise - there might be better bonuses in the game... Any ideas?

[SGT Rud]

It would be nice if the faction bonuses all covered fortifications. I like that idea. Would be horrible trying to take them down, but would be nice to help keep our up.

[MSH]

@ SGT Rud I know that the idea is nice - am just wandering, whether the assumption itself is correct :)
On one hand, walls are buildings, so at least theoretically, their defenses should increase with the "building defense" bonus. On the other hand, everyone seem to agree that the walls were easier to demolish this time, then during BfG despite all the bonuses which people were using.

The question, therefore still stands - does "building defense" bonus affects walls in any way, or not?