Fortification armor enchantment vs penetrating strike

[Jonjonjon4]

Hello masters and adventurer's.

A question popped up at my table.
The rogue class feature variant "penetrating strike" deal damage against the enchantment "fortification"?

Penetrating strike allow the rogue to deal half of his backstab damage against creatures imune to backstab.

Fortification give you a chance to deny backstab damage. (100% on the best upgrade)

[Elkad]

I've no idea if there is a specific ruling, but it should be full or half, depending on the armor check. (Always half at 100% fortification)

[ciopo]

I could see it interpreted in either direction, and if I had to rule it I would rule it in favor of whatever is the resource in the PC possession.

I say "either way" because on how fortification is worded, it is not immunity to sneak attack/critical hits.

fortification is "roll a d100, if it's below VALUE, that precision damage you were taking is prevented", so it can fairly be read as the rogue rolling the full SA dice amount, because the target is not immune to sneak attack, then the target rolls his "chance to evade sneak attack"

that functionally it's 100% chance on heavy fortification does not weight onto it, the rogue is still rolling the full sneak attack damage -> penetrating strike does not trigger.

But if it's a PC rogue attacking an enemy with fortification, I'd grant it, but I do not feel that is the RAW of the matter.

[sleepyphoenixx]

I agree with ciopo (on the RAW). It's not SA immunity, it's negating SA damage. Penetrating Strike doesn't trigger.

I also wouldn't houserule it differently. Unlike type-based immunities like undead Fortification is rare enough that it doesn't need a blanket counter.
Rogues get UMD for a reason. Either find a different way to deal with it if it comes up or accept the fact that your one-trick-pony build isn't going to work in every situation.

[Biggus]

I agree that a strict interpretation of the rules would not apply penetrating strike to fortification as it's not described as immunity but "a chance that the critical hit or sneak attack is negated". I don't think it would be unreasonable to let it work personally, but RAW it doesn't.