The rules for cover state that half and 3/4 cover grant a bonus to both AC and (importantly for this question) Dexterity saving throws. However, some spells, like fireball, state that the area of effect spreads around corners. So, if a creature has half or 3/4 cover (or even full cover) between them and the center of the sphere of a fireball, do they get a bonus to their saving throw against the fireball's effect, or is that bonus negated by the fact that it spreads around corners? (In the case of full cover, assume that there is open space for the fireball to spread around/over the cover, e.g. a 6-foot tall wall.)
[RPG] Does cover help against spells/effects that spread around corners (like fireball)
area-of-effectcoverdnd-5espells
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Best Answer
If the effect can spread around the cover to reach behind it, the target gains no benefit from the cover
Jeremy Crawford, official 5e rules designer, addresses this specific situation here on Twitter:
If you're in a solid concrete bunker with no openings, the enemy can't target you with such an effect because there's no way to reach you - but if there's just a short 5-foot wall, fireball can easily spread around that cover to reach you. If the fire is able to spread around the cover to reach you, that cover grants no benefit because you're still in the area of effect.
Spell areas in the shape of a sphere normally extend in straight lines from the point of origin to the radius of the spell. All spell areas of effect are described similarly:
Thia is further clarified under the rules for targeting, specifically requiring a clear path to the target:
As such, normally, spherical spell areas will be blocked by cover; a solid wall would mean that any area within the radius that is blocked by the wall would not be within the area of effect, even if the spell extends to the left and right of the creature behind the wall.
Fireball specifies that "The fire spreads around corners." because it ignores this restriction. If there is any part of the area behind cover within the radius, and that part is not totally blocked from the parts affected by the fireball, it is also in the area of effect. A single 5-foot wall, for instance, won't protect you from a fireball unless you're just outside the area of effect already.