Should breaking down something like a door be adjudicated as an attempt to beat its AC and HP, or as an ability check against a set DC?

Question

It is not uncommon for players to encounter a door that resists being opened - the door may be stuck, barred, locked, barricaded, etc. A locked door could be unlocked by finding a key or passing a Difficulty Check to pick the lock, or it could be broken down.

In the D&D 5e Dungeon Master’s Guide page 237, the examples for when a strength ability check might be used are: “Smash down a door, move a boulder, use a spike to wedge a door shut”. Which seems fine - set a DC and see if the player can beat it with Strength check. This seems to be confirmed by the Player’s Handbook page 176, again in reference to when a Strength check may be used: “Force open a stuck, locked, or barred door”.

However, page 246 of the DMG also details object Armour Class and Hit Points. One could argue that a door is considered to be an object (at least, as much as a wall is considered to be an object by the book). Lets say the door is made of wood, its a medium sized object and it is resilient, so it has an AC of 15 and 18 Hit Points. When the door reaches 0 HP, it opens.

When would it be appropriate to use the AC and hit points of a door to determine if it opens versus setting a DC Strength check?

For the purposes of this question, assume there is always a chance for success and a risk of failure, there are no automatic successes or failures. Also assume that the players are determined to break the door, they are not interested in looking for ways around it - the door will be broken and open eventually, it is more a case of what method should be used to determine when the door opens.

---

Note that although this question is specifically asking about breaking doors, it would apply to any situation where it might be appropriate to use either an AC or a DC to break something. I have simply used doors as my example as they are one of the most likely and most common things a player may try to break.

Answer 1

In my interpretation, the AC VS DC thing depends on how the PC would like to open the door.

DC would mean the character wants to keep the door whole, but just get rid of whatever would stop the door from opening (like the small metal part of a lock sliding into the side of a wall or a wooden bar behind it). This might leave the door damaged, but still usable (depending on the lock method).

AC would mean a player attacks the door, so they would just physically destroy it, which I would just describe as a player trying to return a wooden door back to some planks with nails sticking out or something similar.

Answer 2

Both are appropriate for different circumstances

The description of how the player wishes to open the door is key. Typically if they wish to 'Smash down a door' - i.e. break it off of it's hinges, a strength check would be the appropriate choice, with a DC determined by the DM according to the description of the door.

If the PC wishes to directly attack and damage the door itself, then AC should be used to determine if they're capable of dealing sufficient damage.

One caveat of letting a PC use AC to attack a door however, is that they'd eventually be able to break even the strongest of doors with enough attacks. If you don't wish the door to be eventually broken into by anybody - a strength check is a single determination of whether a PC is capable of it or not.

Answer 3

It depends on the Situation

Is there a penalty for failure, and how detailed do we really need to be?

Scenario 1

If your party is in the middle of a combat and needs to break through a door, then how long it takes them matters just as much as how hard they hit. There is definitely a penalty for failure here, and as it is combat, and thus a tense situation where every action matters, we want to be detailed. Thus, use AC and hit points.

Scenario 2

If your party is not threatened, has plenty of time, and there is no penalty for failure, you don't even need to roll. Look at the proposed DC, look at the characters and how they intend to do it and make a judgement call. If they have any chance of success, they'll get there eventually so just narrate it happening. If there is no chance of them achieving it, perhaps because they're all Strength 8 wizards with just their fists against a locked iron door, then you just tell them they have no chance.

Scenario 3

But what if there is a penalty for failure? Maybe there's some unsuspecting monsters on the other side, who could be taken by surprise if you successfully kick the door down on the first attempt, but will be able to react if it takes longer. We could make attacks against the door until it breaks, and decide that if the players do not break the door in X turns then the monsters will have had time to prepare a defence. But in practice, all this will turn into is a bunch of meaningless dice throws. Nothing has changed from the players' point of view, so they're just going to keep hitting the door again, and again, and again, until the door breaks. That is a boring waste of precious table time.

So instead, roll against the DC. If your players make the roll, they did it quickly enough that the monsters are still napping, playing cards or whatever. If they fail, they had to hit the thing enough times that the monsters were able to ready a defence.

In conclusion

Don't roll the dice any more than you need to. If there is no penalty for failure and a chance to succeed, give it to them. If the failure doesn't get any worse if they repeatedly fail, just roll once against the DC. If it really does matter exactly how long it takes to break the door, and you really need to know exactly how many hits it will take then, and only then, use AC and hit points.

A caveat is if your players want to give the door an opportunistic kick, just to see if it'll open, without investing all the time necessary to guarantee that the door breaks. In this case, roll the DC once. If they make it, great! If they don't then anyone on the other side knows they are there, so you don't need to bother rolling again.

Answer 4

They both solve the same problem

Both DC and AC handle the same situation, they just have different ways of handling it. There is no right or wrong choice in which to do. The choice should be made considering what feels right for the encounter, what the DM/players prefer, and the skill set of the party involved.

When to use DC

DC tends to be the simpler solution. Typically breaking down a door requires one roll per attempt and without HP there are less numbers to keep track of. This makes the encounters more streamlined and feel fluid. I have found that using DC tends to be more cinematic and players who enjoy the role-play prefer this option.

Against stronger doors you could even create a situation with sequential DCs they need to beat to break it down. For example, an iron door would be much harder to break down by brute force, but that won't stop the barbarian from trying! Set the door with 3 DCs to beat. I opt for starting with a high DC then lowering the following checks as the door takes mores damage. The first cause the door to bulge, the second breaks the hinges and bends the door, the third rips the door off the hinges and sends it flying into the room.

When to use AC

AC has more factors to consider. Treating a door as an object you have to consider its HP, its AC, and any damage reductions it may have. It also helps when your party overall has a low strength save and beating strength DCs is difficult and takes multiple attempts. This also enables casters and non-melee characters to help break down the door. Players who enjoy number crunching or parties with low strength checks would likely prefer this solution.

When you have stronger doors and it is unrealistic to break them down with brute strength, it's more appropriated to stat the wall with AC/HP. Giving a door more HP, a higher AC, or modifying its damage reduction is an easy way to increase their difficulty.

Also I've ran sessions with people who hold grudges against doors and watching the HP of a door whittle down until it eventually breaks gives them an odd sense of satisfaction.

---

This answer is based on encounters in sessions I have ran or played in. My opinion based on my personal experiences and are by no means a large study. There are times when I use both methods, but my preference is to use DC.

Answer 5

I always change it based on what the door is made of and what the players is doing.

If the player says they are going to shoulder check the door that is obviously a strength check if they say they are going to use an axe to chop through the door that is attacking the door. I never let my players just say "I am going to try to break the door down" my immediate response is "How? How are you trying to break it"

But I limit what the players can do (or at least what works, hey you can try anything) based on the door material. You are not chopping through an iron door no matter how many times you hit it with the axe, the object damage rules support this with something called a damage threshold and damage immunities. For instance I always rule slashing don't work on stone or at least not unless you are doing at least 30 points of damage with each attack, so generally a strength checks are all that is possible. A stone door might be possible to break with a hammer or heavy pick but almost no other weapon is going to leave a mark but a strength check is always possible even if impossibly high. this mechanic is great for mitigating what I call tomfoolery, like players attempting to cut a rope with a sling or club or trying to smash down a wooden door with a rapier.

A homebrew thing I sometimes do is say every attack does 1 point of damage to the weapon or 1d2-1 if it is an very sturdy weapon, this keeps players from just always relying on breaking things down, now they might destroy their weapon if they get unlikely with their rolls to chop through the door. Usually I save this for sturdy objects like metal or stone, but wood might be appropriate if the players are trying to dig their way through a iron bound wooden door with a sword or a low level monk tries to punch their way though an solid oak door. It makes the layers stop and think which is always a plus.

Answer 6

In Moments of Building Tension

Whilst it may be better to abstract the damage as User Kyyshack said in a comment:

If they roll an attack, what will players do if they don't get through in the first hit? Nothing has really changed so they'll just hit the door again. And Again. And Again. Until the door is broken. That's super boring and wastes time. It's much better to abstract that boring time away behind a single roll against a DC that will answer your question of "Do they break through quickly enough to catch the monsters off guard?"

Using the rules for Object AC and Hit Points could be useful to help build tension. Rather than having the PC’s roll over and over again, you could have monsters roll to see if they damage a door the PC’s are on the other side of. Seeing creatures claw through a door or ripping boards off it would create more tension than if they rolled a nat 20 and broke it down in a single turn. The former option might allow players more time to react to the issue and respond to it, such as by barricading the door, escaping, preparing an ambush, etc.

Additionally, having rickety old damaged doors or furniture can help to establish a theme. If players find a door that has already been damaged, they may want to investigate what caused it, and if that thing is still around. For example, if they found a door with a large axe wound in the middle of it like something out The Shining, players may wonder who was trying to get into this room, and why? Or, if they stumbled upon a door with a dozen puncture wounds in it like it was repeatedly stabbed by a dagger, they may investigate the cause - or not, but they’ll learn pretty quickly what caused those holes when they get hit in the back of the head by a falling flail trap.

Partial Opening

Thanks to user Jared Posch for highlighting the idea of accessibility in their comment:

I would look at the accessibility of the lock, aka, can the players actually attack the lock. A door locked with a wooden beam would mean the beam is behind the door, so unless a player can accurately swing his sword down the middle, I'd say they don't do damage

Rather than players having to completely open a door (such as by destroying it completely or by bashing through the door with a DC Strength check), players might partially damage a door.

• For example, players might cut a hole around the locking mechanism to open a door, leaving it damaged but mostly intact - perhaps only removing 1 or 2 HP from the door.

• Or, players may cut a hole in the door, creating an opening large enough for a Small creature to go through (or a Medium sized creature if they squeeze through the hole). This could be useful if they know they are being chased by Large creatures as it would slow them down. Alternatively, Small creatures like Kobolds might make holes in locked doors as it would slow down Medium sized creatures, hinger Large creatures but would not affect Small creatures like themselves (or they could make Tiny holes so they could squeeze through but larger creatures wouldn’t be able to).

• Players may even put a hole in the door to gain access to the lock or door bar on the other side, allowing the door to be easily unlocked.

Treat the door as though it was made up of smaller objects. So, whilst you may need to remove 18 HP to destroy a Medium sized resilient door completely, you may only take off 5 HP to put a Tiny hole in it or 10 to put a Small hole in it.

Reinforced Doors

User guildsbounty helpfully pointed out:

Perhaps worth noting: some published adventures explicitly call out that a properly fortified door cannot be kicked in with a Strength Check, and must instead be destroyed by attacking it. The most recent example being in Ghosts of Saltmarsh.

Having this clear distinction for Reinforced doors could be quite a useful tool. It may force players to make a decision between completely breaking this door, which would be very noisy and may take a long while, or finding another way through it. Here is what the Ghosts of Saltmarsh says about reinforced doors, page 157:

It takes a character 1 hour to gather the required materials and reinforce one door. The time is cut in half if another character helps. A reinforced door cannot be broken through with a Strength check, but must be battered down (AC 15, 30 hit points, immunity to poison and psychic damage)

Note that this rule is assuming the door is made out of wood, is being reinforced with wooden planks and nails and these materials are readily available.

A possible way to calculate the health of a reinforced door is to add the health of the reinforcing objects to it and use the highest AC. For example, a Medium Resilient wood door (AC 15, HP 20) is being reinforced with Small Resilient planks of wood (AC 15, HP 10). The highest AC is 15 so the door has an AC of 15, 20 HP plus 10 HP equals 30 HP, giving us AC 15, HP 30 for the reinforced door in question. If we were using steel bars to reinforce the door instead, as they have an AC of 19, we would instead have AC 19, HP 30 for the reinforced door.

So then, one possible situation where you would use AC and HP over a DC check is when a door has been reinforced, either by the players or by the inhabitants of a dungeon.

Hitting Creatures Behind Cover

This follows up from the idea of partial opening. I got a bit carried away but this highlights how object AC could be used in a completely different way than how a DC check is used:

A creature can use any suitably large object as cover from an attack. A creature gains bonuses to their AC and Dexterity saving throws depending on the level of cover. A creature in total cover gains the bonus of it not being able to be targeted directly.

If, for the purposes of an attack, we treat the door as a creature, we can use the Cleave Through Creatures optional rule in the DMG page 272:

When a melee attack reduces an undamaged creature to 0 hit points, any excess damage from that attack might carry over to another creature nearby. The attacker targets another creature within reach and, if the original attack roll can hit it, applies any remaining damage to it

So, using the example of a door, its a Medium sized resilient object made of wood, so it has 15 AC and 18 HP. However, we are targeting a Tiny section of it, so the AC is 15 and the HP is only 5. The attacker rolls a 16 and deals 7 damage, this hits the Tiny section of the door and reduces it to 0 HP. As we are using the Cleave Through Creatures rule, the attacker still has 2 damage left over which can be used to hit a creature within range (such as one who was standing right behind the door).

Because the weapon has now gone through the cover, the creature is no longer in cover for the purpose of this attack - just to be clear, any bonuses for cover (such as increased AC, better Dex Saving Throws or being untargetable) the creature had are being ignored by this attack.

If the 16 rolled by the attacker earlier to hit the door is enough to hit the creature behind the door (without any bonuses from cover) they will take the remaining 2 damage. If the creature had an AC of 17 though they would manage to avoid any damage.

This rule would make more sense when applied against a creature behind a fragile material, such as glass. (Due to glass only having an AC of 13 and being fragile, a Tiny section of that might only have 2 HP, meaning more damage is transferred to the target). It also makes sense thematically, Rules as Written would say standing behind a glass window or a curtain or even pulling the bedsheets over your head would count as cover, they might even count as Total cover, preventing the creature from being targetted. However, by using the Cleave Through Creatures rule in this way, we can make things more realistic “that window will not stop this arrow going through”, “those curtains or those bedsheets aren’t going to stop my sword from stabbing you”.