How much damage does adult Blue's lightning breath do to structures?

[Pinjata]

So, we have a situation where Adult Blue Dragon is flying over a small town, with a stone fort in its center. Dragon is there basically to cause fear. But flying devastator also has a destructive itch. He targets roofs and prioritizes the fort. I'm wondering how much damage could his lightning breaths do? A bit maybe in term of numbers, more in term of fluff. I'd imagine his breath would equal a shot from early period WW2 anti tank gun. Something that could eventually even damage the fort and make it crumble slowly.

thoughts?

thanks :)

[Demonslayer666]

I would say lightning would do at least a little damage, and could do all the way up to exploding stone. Just narrate the building loosing bits of rock and cracking with each strike, charred rock and dust/smoke, wood burning, maybe a wall or corner crumbling after a while.

How damaged the building is, is completely up to you, and where you want to take the story. Do you want it destroyed, badly damaged, in need of some repairs, or left with lots of cosmetic damage?

[Ninja_Prawn]

I would generally not grant buildings any special resistance against lightning damage. Lightning can definitely blast apart wood and stone - I've seen it happen, or at least the aftermath.

Therefore, each blast from the dragon is doing 66 points of damage on average to any building it hits.

Extrapolating from existing rules, I would estimate that a 10' x 10' x 1" section of wall has 30 HP. The AC would vary depending on material, but obviously isn't relevant against dagonbreath.

So how thick is a roof? Maybe 2"? In which case every lightning bolt would blast a 10' square hole in a roof. Where I live, the default thickness of traditional stone walls in domestic buildings is 24" so that would have 720HP per section, and be able to resist sustained dragon attack for over a minute.

A castle will have walls several feet thick and might well have vaults/casemates that are protected with several feet of material (probably earth) on top as well. So that ought to be relatively safe from your dragon, by my calculations.

Remember though: lightning starts fires, which are a huge threat in medieval settlements. That's the real threat here. If the dragon gets a good fire going, the townsfolk are in for a bad time.

[Vogie]

Remember though: lightning starts fires, which are a huge threat in medieval settlements. That's the real threat here. If the dragon gets a good fire going, the townsfolk are in for a bad time.

Also, there is a connection in-game as well - Lightning Bolt has a "The lightning ignites flammable objects in the area that aren’t being worn or carried" rider in it, so having Dragon's lightning breath do something similar isn't that much of a stretch.

[Pinjata]

Great solutions guys, just what I needed :)

[Chronos]

A dragon's breath would be even more effective at starting fires than natural lightning, because natural lightning usually strikes when it's raining. But a literal bolt from the Blue, when all the thatch in the town is dry? Big trouble.

[Aprender]

If you're the DM, it will do whatever it needs to do to accomplish the narrative you have in mind.

[Tanarii]

It does the equivalent of 4 shots from a ballista, 2.4 from a mangonel, or 1.5 from a trebuchet or cannon. It does enough to take out a Large (10x10) object 2.4 times over. 5 blasts will sink a sailing ship or a longboat. It blows right through a Wall of Ice, and can blast away 2 inches of a Wall of Stone panel (which are either 3" or 6" thick)

It's almost certainly going to blast right through wood and keep going, and do solid damage to a stone structure after a few blasts. (Wall of Stone is probably significantly stronger than the average man-made structure of the same thickness.)

[No brains]

If you want to be technical, 0. Their ability only says it damages creatures, not objects.

That said, do what the story needs, etc. If you have a player who loves to live by RAW, give the dragon a magical retainer that allows its breath weapons to start fires. That way you won't have the same player try to tunnel through walls with Shocking Grasp.

[Ninja_Prawn]

Why shouldn't a player be able to tunnel through walls with shocking grasp? I mean, spades and pickaxes would be more conventional, but damage is damage. If you're willing to spend hours at it (which is what it would require, looking at the back of my envelope), I'd let you electro-punch your way through a wall.

[No brains]

Why shouldn't a player be able to tunnel through walls with shocking grasp? I mean, spades and pickaxes would be more conventional, but damage is damage. If you're willing to spend hours at it (which is what it would require, looking at the back of my envelope), I'd let you electro-punch your way through a wall.

I'm actually not sure why the rules are that way. It's a weird issue, but my guess is that many spells don't damage objects as a way to get around complicated rules of energy types interacting with materials. Further, you won't need to worry about every aoe destroying a part of the floor.

To me, it makes sense that any damage type can vibrate the molecules of matter out of their useful alignment, even with weird damage types like radiant or necrotic. It's just that for whatever reason, these effects are designed not to affect objects.

Just remember that it's entirely safe to cast Wall of Fire on a field of dry grass. For whatever reason, it's one of the few fire spells that doesn't ignite objects.

[HappyDaze]

Many stone structures have wooden roofs (and interior flooring for floors above ground level). A flying dragon can lightning bolt these "tender innards" rather than the hard shell of stone.