Dungeon Master Assistance

Line of Effect Definition for Fifth Edition

The Player’s Handbook says:

“To target something [with a spell], you must have a clear path to it, so it can’t be behind total cover. If you place an area of effect at a point that you can’t see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.”

This isn’t especially clear and and leads to many questions.
A clear definition of “line of effect” would clear up much of the confusion. However, neither the Player’s Handbook nor the Dungeons Master’s Guide use this term at all. Because fifth edition doesn’t define a line of effect, below is my unofficial definition. I went back to the definition in third edition and modified it to account for the differences in 3rd and 5th edition. Because the following is not official, you should consider it a house rule.

Line of Effect [for Spells]

You must have a clear line of effect to any target that you cast a spell on or to the point of origin for any spell’s area of effect. A spell’s area of effect affects only an area, creature, or object to which it has line of effect from its origin.
Line of effect is a straight, unblocked path that indicates what a spell can affect. A line of effect is canceled by a solid barrier. It’s like line of sight for ranged weapons, except that it’s not blocked by fog, darkness, and other factors that limit normal sight.
A line of effect is also blocked by a solid barrier that doesn’t block sight, such as clear glass.
An otherwise solid barrier with a hole of at least 1 square foot through it does not block a spell’s line of effect. Such an opening means that the 5-foot length of wall containing the hole is no longer considered a barrier for purposes of a spell’s line of effect.
Line of effect is required for spells unless the spell description specifically states otherwise. Any spell that says that you need to see the target still requires a line of effect. If the spell description says that an effect spreads around corners that effect doesn’t require a line of effect.

Concentration Spells

If a spell must be maintained with concentration, you must have a line of effect to cast the spell, but you do not need to maintain a line of effect to maintain concentration. However, if the concentration spell allows you to use an action, bonus action or reaction to effect a creature or object then any round that you perform that action you must have line of effect to the target.

Line of Effect [for Auras]

The line of effect for an Aura is different than for spells. To be effected by (or to detect) an Aura there must be a straight path to the source of the aura that isn’t blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.