[TW 2013] Shooting through cover

[Michael Lewis]

How do you determine if you hit somebody shooting through their cover?

For instance, someone is in a house shooting out of a window. I'm assuming that a bullet will go through siding and drywall. If the armor doesn't stop all the bullet's damage, how do you determine if the bullet hits him or her?

Or do you even bother and just say bullets won't go through the walls to improve player/npc survive ability?