Tempered Faulds work just fine against damage barriers. The effect of the faulds isn't limited to specific types of attacks. It can work against conjurations, equipment, and even against damage barriers. If the attack rolls the effect die, the faulds work and can force a reroll. That's all there is to it.
The Roll Dice step is where this ability would apply. If you roll the effect die, the Faulds can force a reroll of it. It doesn't matter what other steps happen or don't happen. Of course, if you skipped the roll dice step, then you couldn't use the ability, but in that case it wouldn't really matter, would it?