D&D 5E Dragon's breath weapon vs wall

[Nitrosaur]

Hi there, first time poster here.

I'm planning to throw an adult red dragon to my party's fort, and was wondering how would it's fire breath interact with their stone walls. Each 10x10 section of the wall has 17 AC and 27 HP, and the dragon's breath does 63 fire damage on average. The cone doesn't reach around corners, so they have that going for them.

Would you have each section of the wall nside the blast take full damage? I was thinking about treating it like the sleep spell, with each section of the wall starting in the center of the blast subtracting damage and carrying it over to the next one until it hits 0 damage. Would you also give stone walls fire resistance? I believe RAW they are immune to poison and psychic, and while it doesn't say anything about fire, they spent a lot of money on making those walls out of stone.

I want the dragon to feel like a force of destruction, but I don't want it to erase everything the party cares for. I want to be as fair as possible, how would you guys rule it?

 

[commandercrud]

Full damage each section. Even with resistance, the dragon would obliterate the wall very quickly. An adult red dragon is a force of destruction. Don't gimp it.

 

[Oofta]

I've never hit this. Where are the rules for HP for building materials?

Fire can damage stone but it takes a lot of sustained heat. I'd probably require repeated breath attacks ... or just different tactics.

Which is not to make dragons any less of a threat, just not able to destroy solid stone with a single breath weapon attack. Their breath weapon is no more damaging than a couple of fireballs (or a couple other spells), I wouldn't allow that to burn down walls either.

Dragons should be dangerous foes but if I look at a rule and think "that makes absolutely no sense" I change it. On the other hand, the dragon picking up boulders weighing close to a ton and dropping them on the keep is a tactic I'd consider.

 

[Cap'n Kobold]

I'd have the breath set fire to doors, shutters etc, but I wouldn't have it actually destroy the wall. Building stone is pretty impervious to fire.

However I'd definitely have the dragon able to smash the doors to kindling with a couple of tail swipes if it can.

 

[Harzel]

I pretty much agree with @Oofta and @Cap'n Kobold - it should be difficult to damage stone with fire, regardless of the source, but that is far from the only kind of damage a dragon can cause. Also, why would a dragon breathe at the wall when it can breathe down on the things behind the wall from above?

With respect to dragon's breath going around corners, I'm not aware of a rule that says it does or doesn't. Spell effects don't go around corners unless the spell says they do, but dragon's breath is not a spell effect. One could apply the same meta-rule to dragon's breath, but it would seem extremely odd (to me) if at least the gas-type breath weapons did not go around corners even though the descriptions don't say they do.

 

[Baron Opal II]

First, your units are mismatched. You're talking about hp for sections of wall and damage from a single attack that may or may not strike multiple sections of wall. I would consider how many sections of wall would be struck by the dragon's breath and compare the hp total with the breath damage. So, if the dragon is going to breathe on four sections of wall at the same time, it will remain standing, the first time.

That said, after a fly-by or two, every exposed wooden section of the structure would be on fire. Afterwards the walls would be scorched and partially melted together.* I imagine that if the stone is hot enought to partially melt, any wood touching it would start to burn. A tail lash would like knock down weakened stone work.

How big is the breath weapon compared to the size of the castle. I think it might be foolish for the dragon to get this close, but if it landed in front of the wooden castle gate a single breath would destroy it.

I wouldn't have it flow around corners, but if you are right next to it I would consider you making a save for half vs quarter damage. It makes sense to me that hiding behind some stone should count for something. Still, you're right next to some hot magical fire there, and there is a lot of radiant heat I would imagine.

They had better have some ballista or some good archers. They're in trouble.


* There was something I saw somewhere about partially vitrified stone walls in England I think. Might be interesting to research.

 

[Flamestrike]

I'd have the breath set fire to doors, shutters etc, but I wouldn't have it actually destroy the wall. Building stone is pretty impervious to fire.

Harrenhal?

When the sun had gone down, Aegon flew Balerion high above Harrenhal, before plunging down upon Harrenhal, burning the castle beneath him. All that was flammable, both suplies and ironmen, caught fire within the castle, while Harrenhal's stone towers cracked and melted. The rivermen outside observed that the towers glowed and melted like candles

Burning of Harrenhal

Dragon fire from an old Red Dragon isn't a campfire here. It's doing as much damage as magma.

It requires between 600-1000 odd degrees Celsius to melt stone. Id happily rule sustained blasts from an Ancient or Old red dragon can melt it.

For mine?

Firstly I'd keep the walls AC the same, but double the HP and do the walls in 20' x 20' sections. The bigger sections justify the doubling of HP, and the doubling of HP means the walls are not insta-gimped each time the dragon breathes on them (it represents the structural integrity the PCs paid so much for). So 54 HP per section. With 60 or so points of average damage per breath weapon attack, that sounds about right.

Then id give them fire immunity, but also give the following rule to dragon breath:

''If a wall is subject to dragon fire by a dragon within half range of its breath weapon, one 20 foot by 20 foot section of the wall loses its immunity to fire damage until the end of the dragons next turn.

''For each 20' by 20' section of wall destroyed, place a 20' by 20' area of difficult terrain adjacent to the damaged wall section. The first time on its turn a creature enters those squares, or if it starts its turn there, it takes 5d6 fire damage.''

So the dragon 'softens' the wall with a breath weapon attack, and then if the dragon hits it again the next round (presuming they get a breath recharge) it likely melts, creating an area of molten rock as difficult terrain nearby.

It gets up close and hits the walls with sustained dragon fire. Sounds about right.

 

[Chaosmancer]

For a story/ cutscene moment I had a high level druid who used Shapechange to become an Adult Red Dragon, they blasted an evil priest that was talking about committing atrocities against the druid's people with point blank enraged fire.

I had it melt the stone of the pryamid, causing a lot of structural damage.

But that was one part story (she was enraged beyond reason) and one part mythos (dragonfire is unlike normal fire in my settings)

So, the first question is whether you want Dragon Fire to be special in anyway. If you do, then I'd take Flamestrike's idea about combining the sections of wall and roll the damage. Maybe not melt it the first time if it doesn't make sense to you, but "weakened stone" is a thing and you could show the wall won't hold against another assault like that. Also, the Players will get terrified of that breath if they see it melting through stone, that is the sort of thing that they don't expect to see, and will jar them into "holy crap this monster is terrifying".

If you don't want it to be special, then don't melt the stone. The fire only exists for a few seconds, and while it will scorch, it might not melt.

But as for your players hard work, 1) I think the set piece of the dragon is worth it and 2) Just ask them how much worse they think it might have been if they had wooden walls when the dragon came knocking. At least the stone has a chance.

 

[Iry]

Different materials should have different resistances. It's pretty reasonable for stone to have fire and cold resistance but not acid resistance.

 

[Chaosmancer]

Different materials should have different resistances. It's pretty reasonable for stone to have fire and cold resistance but not acid resistance.

Eh, maybe?

I mean, sure, stone doesn't break easily due to heat, but thermal expansion and contraction is a serious concern with stone buildings. And dragon's breath is hot. Hotter than a flamethrower, it is more akin to the heat from a lightning strike, and that can crack stone in half.