Dungeons and Dragons 5th Edition has a fairly small section on how to rule dealing damage to objects. This is the amount of damage an object can take before it’s broken and not necessarily how much damage to destroy the substance. All objects are immune to poison and psychic damage and otherwise, just have hit points based on size and fragility. It’s fairly simple and leaves a lot to ‘make your own judgement at what makes sense’. Which is good for ease of use but my brain is often obsessed with the consistency of a rule to create a consistent simulation.
When looking at objects we are thinking of size, substance and density. So the following is a detailed expanded table of possible objects – what damage they could be resistant to and vulnerable to. I have tried to account for what substance an object is to determine if it can be affected by attacks from objects made of other substances and the normal 5th edition damage types. Reading left to right a vulnerability overrides a resistance and an immunity overrides everything. You can only benefit from one resistance or vulnerability – they do not stack. Magical weapon attacks bypass resistances and immunities. Note that some objects are especially vulnerable to attacks from tools designed to break them. I have listed a few options but more could easily turn up in play.
Breaking down a door.
Detailed rules for forcing open or breaking down doors are missing from 5th Edition. We only have a mention that a Strength/Athletics check may be called for forcing open a locked or barred door. Here is some suggested DC’s door by what substance it’s made out of.
Damaging a Block of Substance
For damaging huge and gargantuan objects add a damage threshold as suggested in the DMG (Dungeon Masters Guide). If the damage dealt is less than the threshold then no damage is taken. If it meets the damage threshold then all damage is taken. For instance, dealing 9 points to something with a threshold of 10 deals no damage but dealing 10 points of damage to something with a threshold of 10 deals all 10 points of damage. The DMG lists this as an option for very large objects such as a gargantuan statue or a massive ship.
Here I have proposed a guide for damaging a block of a raw substance. This method comes into play when damaging a solid mass such as a massive stone wall. In such a case the damage received is able to destroy a 5-foot area and a depth as per below. Each depth has hit points of a large object.