Friday, January 16, 2015

D&D 5e Armor as DR

D&D Armor As Damage Resistance

Douglas Cole wrote about this on Thursday - essentially, porting the approach of GURPS combat to D&D 5e.

Here is how I think it could be implemented.

Armor reduces damage, bonuses improve AC - Armor doesn't provide improved AC. Only Dexterity, magical protection, shields, etc. provides improved AC. Actual armor (including pluses from magic armor) just reduces damage via a mechanic called Damage Resistance (DR).

For example, Plate is AC 18, no DEX bonuses. You get +2 from DEX, +1 from a shield, and +1 from a Ring of Protection. Because of the heavy armor, you ignore the DEX bonus. You have AC 10+1+1 = 12 and people roll vs. that to hit you. If they do, subtract (18 - 10) = 8 from their damage.

Chinks/Gaps in Armor - You can attempt to bypass some of the armor of your opponent. The attack is at Disadvantage, and you can't do this if you are already attacking at Disadvantage. If you hit, your opponent's DR is halved, round up.


There are a few challenges.

Monster AC - You'll need to note the DR of monsters, which would be AC - Dex adjustments - non-armor bonuses - 10. So a critter with AC 16 (Natural Armor) and a DEX bonus of +2 would have 16 - 2 - 10 = 4 DR.

In addition, you need to know if their armor is Heavy, and thus is already forgoing a DEX bonus, or not.

Balance - D&D and its hit points are balanced around the abstraction that armor reduces hits, not reduces the damage of hits. Low damage monsters will become harmless, which reduces the effects of bounded accuracy (the relatively low ACs of 5e monsters.)

Lots of Decision Points - You will need to constantly evaluate magic items, effects of powers and spells, and so on for their ability to reduce hits (increase AC) or reduce damage (increase DR) - nothing can be used just straight-up.

These aren't small, but springing off of Doug's idea, this seems like something ready for playtest and to run with if you prefer the GURPS-like effect of armor reducing damage instead of reducing the number of hits.


  1. I did some thinking about this here. Specifically, it's about implementing DR in D&D. It's something that comes up pretty often, but I'm still not sure if the challenges you mention outweigh the perceived problem.
    We arrived at mostly the same challenges/issues. One more that struck me is how disheartening it can be for PCs to see a great attack and damage roll reduced to nothing ("I Hit Him! Finally!") after DR is applied. Most other mechanics in D&D tend to tie resolution to the d20 roll, but DR seems to add another layer of resolution on top of this, and this seems to de-emphasize the results of the d20 roll. It seems like it snatches that perceived victory and elation out of a player's head and hands in D&D. Other systems do manage it better, but as Douglas mentions, they're usually trying to more expressively model the actual exchange on a one-for-one basis.

    1. I think attacks bouncing off of monster's DR would only be disheartening if the players aren't onboard with the idea of armor-as-DR. I find it equally disheartening at times when my Swords & Wizardry guy is hit and my plate armor doesn't let me shrug off a dagger strike or a skeleton's claws. But once you accept that's how it works - and that you'll be hitting much more often this way - it wouldn't be much of a player morale issue. The real questions is if DR throws the balance of weapon damage vs. HP hopelessly out of whack, and adds work to implement in a fun way.

    2. I agree that with buy-in, anything is possible. I keep Hit Points pretty abstract, and try to convey that the attack roll is more of a series of feints, strikes, parries, and so forth looking for an opening.
      It doesn't strain belief that a dagger can find a vulnerable spot on someone wearing plate. There's nothing about plate that makes it intrinsically immune to being circumvented through luck, skill, opportunity, etc. :)
      The balance is definitely an issue. Hitting a guy with a d4 dagger, when he has 5 DR creates the imbalance. Unless you graft on Criticals bypassing DR or something similar, you've got a situation where the foe is effectively impossible to damage.
      My main concern is just that it adds another level of resolution by effectively bypassing the results of the "hit roll." If you need lots of hits, narration of combat results can accomplish that. The only thing "hit" really conveys in D&D is that the result is damage dealt. A lower roll can just as easily strike the target in the fiction, but it just doesn't have the oomph to overcome armor, or is deflected away from a vulnerable area :)

    3. I get the whole nature of D&D combat abstraction. I included a way to reduce DR, above, and it's easy to say criticals do that automatically. I wouldn't put a system like this in place to improve narration, but to change the way the game plays out combat. It's not about the narrative play but the actual results of die rolls I'd want to change via this.

      I'm not sure it would work well, but I think this is a workable basis for testing if it would work well.

    4. Gives me an idea for 5e specifically: Advantage/Disadvantage for certain weapons versus certain armors? Advantage/Disadvantage on the damage rolls (take high or take low)?
      I do like the idea of stepping down damage by die size that you mentioned below in response to Random Wizard as well. That seems like it would solve things nicely, without reducing damage dealt to 0.

    5. I thought about advantage/disadvantage for damage as well, as a variant of All-Out Attack - quite the analog to GURPS' All-Out Attack (Strong) as well. Using Anydice, a 1d8 advantaged roll is +1.3 average higher than a flat roll, with a smaller deviation. Just shy of twice as likely to roll an 8, too.

    6. If all I managed to do was spark an idea for another rule to try out, that's plenty of reward for writing the post!

  2. I pondered this same issue a few months back. Well, I wrote about how DR would be a likely consequence of using roll-under action resolution in d&d:

  3. I tried a armor as DR in a game I ran a couple of years ago. I think it works better if you say the DR is variable.
    leather 1d4
    chain 1d6
    plate 1d8
    shield +1

    1. Did you roll for each hit, or mean that 1d8 of armor hit by a 1d12 attack drops the attack to 1d4?

    2. Another variant here would be to treat it as something like

      Leather: 1d4-1
      Chain 2+1d4
      Plate 4+1d4

      That sort of thing - so that the base layer is better and better (and some chinks have a zero, perhaps). You could, with Roll20, even have unusual "dice," so that you could get nearly any total you wanted: such as if you wanted (say) 2d3 or something.

  4. I am actually doing something different in my 5E game:

    1 - armors don't grant AC bonus, but you can apply your Proficiency bonus to AC if you're proficient with that armor (Dex limitations and disadvantage work as normal)

    2 - armors DO grant temporary CON bonus (overcoming the 20 pips limit only in this case), thus a 14 CON fighter wearing hide armor has 16 CON (12-10=+2). If you change armor you need to take rest in order to change the CON bonus properly.

    1. How has that been working out in the game?

    2. It's working out pretty good.

      There's not such a huge loss in term of a AC points, and additional HP points are more than welcome. Players haven't found yet magical armors, but I think that magic bonus will be added to AC as a magical deviation.


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