Damage and HPs of structures

[Hiro Quester]

The Crumble spell (SC 56) does hundreds of years of erosion damage to a fabricated structure.

The text says that the size of the object you can affect increases with CL (Gargantual at 18+). The erosion does 1d8 points damage per CL:, to a max of 10d8.

That doesn't sound like much damage to a stone bridge you are trying to collapse. A full round attack of unarmed strikes from a well built high-level monk, with necklace of natural attacks, could do more damage.

How can you tell how much damage a stone structure can take?

How can a DM determine whether a spell effect like this (or horn of blasting, etc.) is enough to collapse a wall, or topple a tower, etc?

[Telonius]

Well, stone has 15 hp per inch of thickness (http://www.d20srd.org/srd/exploration.htm#). With 10d8, that's an average of 45 damage. Not sure how thick the typical stone bridge is, but 3 inches sounds pretty solid.

[Anxe]

Crumble damages the whole structure, right? While this monk would only damage a 5 foot section with attacks.

And yeah, stone lasts a long time. The pyramids are still standing thousands of years later. There's plenty of less well known examples. This might be accurate for what the spell claims to do.

[Jowgen]

Crumble damages the whole structure, right? While this monk would only damage a 5 foot section with attacks.

10 foot. Large structures get damaged in 10 ft sections unless otherwise specified. But indeed, the spells advantage is that it should damage all sections (RAW is actually a tad unclear there) at once. Plus, you have to factor in hardness, which the monk has to deal with on each hit while the spell ignores it.

Still the spell is rather ineffcient. A 10 by 10 ft wall 1 ft thick made of masonry has 90 HP, so the spell only gets through half of that on average. Even a 6 inch thick wooden wall (happens to apply to most ship hulls) has 60 HP, giving it a decent chance to survive a hit.

[Zancloufer]

I would argue by RAI (since the RAW is somewhat iffy) that the damage is done to the entire structure at once using the smallest numbers possible (IE 15 HP/Inch for stone). Otherwise even at level 18+ this spell is rather, weak. Remember it caps at Gargantuan Size (So ~18000 Cubic Feet) which would only be a 30x30x20 house at most, any bigger object and the spell outright fails.

Unless you want to argue a level 18 Druid using a spell specifically designed to destroy structures can't destroy a single family dwelling if the walls are more than ~3 inches thick (stone walls tend to be BTW).

[Hiro Quester]

I'm actually playing an epic (21) druid, who is about to help invade a fortified castle.

Considering developing an epic spell to take out a section of a castle wall or something like that.

So I'm generally trying to figure out how damage to structures like that works, mechanically.

I think describing the effect in terms of HP damage is not going to be sufficient. I just need to describe a method by which the spell collapses a stone wall.

Perhaps use a crumble-like effect to erode the mortar holding stones together, then have tiny seeds implanted into the cracks and gaps between stones, instantly aging into trees whose roots grow and force the stones apart. (Use conjure and fortify epic seeds.)

Replacing worked stone with a bunch of natural trees growing in a pile of rubble seems a fairly Druidic spell effect.

[Anxe]

I'm actually playing an epic (21) druid, who is about to help invade a fortified castle.

Considering developing an epic spell to take out a section of a castle wall or something like that.

So I'm generally trying to figure out how damage to structures like that works, mechanically.

I think describing the effect in terms of HP damage is not going to be sufficient. I just need to describe a method by which the spell collapses a stone wall.

Perhaps use a crumble-like effect to erode the mortar holding stones together, then have tiny seeds implanted into the cracks and gaps between stones, instantly aging into trees whose roots grow and force the stones apart. (Use conjure and fortify epic seeds.)

Replacing worked stone with a bunch of natural trees growing in a pile of rubble seems a fairly Druidic spell effect.

Is Earthquake off the table?

[ExLibrisMortis]

What about transmute rock to mud (or sand) as comparison point? The spell doesn't affect worked stone by default, but changing that shouldn't be more than a +1 or +2 spell level adjustment. With the vanilla spell, you can undermine the foundations of most walls. Turning a 100x20x20 section of supporting rock (40 10' cubes per casting) into mud should seriously damage the integrity of the wall, especially if you can then remove the mud.

[Goaty14]

What about transmute rock to mud (or sand) as comparison point? The spell doesn't affect worked stone by default, but changing that shouldn't be more than a +1 or +2 spell level adjustment. With the vanilla spell, you can undermine the foundations of most walls. Turning a 100x20x20 section of supporting rock (40 10' cubes per casting) into mud should seriously damage the integrity of the wall, especially if you can then remove the mud.

Transmute Stone to Mud, remove water from mud = really weak dirt.

[Hiro Quester]

I considered earthquake. But it is specifically ruled out


Any structure standing on open ground takes 100 points of damage, enough to collapse a typical wooden or masonry building, but not a structure built of stone or reinforced masonry.

Perhaps an epic spell based on rock to mud could undermine the base of a structure...

[ExLibrisMortis]

Transmute Stone to Mud, remove water from mud = really weak dirt.
Exactly. Easy to repeat a couple of times, too.


I considered earthquake. But it is specifically ruled out
Well, stone structures do take 100 damage as well, it just takes more than one earthquake to destroy them. Granted, spending many 8th-level slots isn't great, but maybe you can gate a spirit of land (MMII), which gets earthquake at-will, along with a ton of other amazing BfC spells. Very druid-like, isn't it?

[Anxe]

I considered earthquake. But it is specifically ruled out



Perhaps an epic spell based on rock to mud could undermine the base of a structure...

It's guaranteed to do more damage than Crumble. True, you'd need six earthquakes to demolish a castle*, but the first one will probably take out most of the defenders.

*3 ft. thick Hewn Stone walls are the biggest written obstacle and they have 540HP.

[Hiro Quester]

Hmmm. 9th level spell UnderMaster will get you an earthquake a round for 5rounds as a SLA. That might be sufficient.

Edit: it also gets a standard action move earth to reshape the ground under the wall. Promising.