# Can you place a web spell on a surface you cannot see?

Situation: target creature is standing on the roof, caster on the ground.

The caster stands at such an angle that he can see the head of the target, but not the roof the target creature is standing on. The caster tries to cast Web (2nd level spell) at a target. There are no 'anchor points', so the caster has to 'layer it across the floor(=roof)'.

Can the caster do this (as he cannot see the roof)?

The spell doesn't mention you have to be able to 'see' the point. But it mentions that if you cannot anchor or layer it across the floor, wall, etc. that the web collapses (and the spell stops after one round).

So can the Wizard layer it on the roof, that he technically cannot see?

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## Yes, he can layer web on the roof, that he technically cannot see.

Web (1) targets (2) a point of origin for an area of effect (3) (within your range).

You have to be able to target a specific point which requires a clear path (4), which you have, the web spell then fills a 20- foot cube (5) from that point. You are not required to see the complete area of effect. So you are not required to see the anchoring points for the layering.

## So how does my spell expand if I don't know where the anchoring points are?

After you have determined the point of origin, the spell’s effect expands in straight lines from the point of origin (3). The point of origin is the only requirement for targeting the spell, the layering is part of the spell. You only decide the cube's point of origin. If the cube is not layered between two solid masses, it ends at the start of your next turn (1).

If you can't see the anchor points for the web, you are effectively guessing where they are and hoping or evaluating that the area you choose will touch those anchor points and allow the web spell to work for its entire duration. In your question, the caster has information of where the roof is based on the presumed height of the creature whose head they can see, so his risk of failing to anchor the spell to the roof is relatively low.

Web (1)

You conjure a mass of thick, sticky webbing at a point of your choice within range. The webs fill a 20- foot cube from that point for the duration

If the webs aren't anchored between two solid masses (such as walls or trees) or layered across a floor, wall, or ceiling, the conjured web collapses on itself, and the spell ends at the start of your next turn.

Targets (2) (PHB 204):

A typical spell requires you to pick one or more targets to be affected by the spell’s magic. A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect (described below).

Areas of Effect (3) (PHB 204):

A spell’s effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn’t included in the spell’s area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.

A Clear Path to the Target (4) (PHB 204):

To target something, 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.

Cube (5) (PHB 204):

You select a cube’s point of origin, which lies anywhere on a face of the cubic effect. The cube’s size is expressed as the length of each side. A cube’s point of origin is not included in the cube’s area of effect, unless you decide otherwise.

Thank you, Ryan Thompson, for significantly improving this answer.

• Thanks for the anwsers. I agree with the above reasoning. I now 'viisualise' the web extending from chosen target point to fill the 20' cube: it will expand/touch onto the (unseen) roof, and anchor there. I assume it partly collapses from 20' cube to the 5' depth layer (as no other anchor points were present, except the rood), and keep that shape during it's duration.
– qsd
Jun 16 '19 at 15:15

# Yes, they don't have to see the surface

The web spell's description says:

You conjure a mass of thick, sticky webbing at a point of your choice within range. The webs fill a 20- foot cube from that point for the duration. The webs are difficult terrain and lightly obscure their area.

If the webs aren't anchored between two solid masses (such as walls or trees) or layered across a floor, wall, or ceiling, the conjured web collapses on itself, and the spell ends at the start of your next turn. Webs layered over a flat surface have a depth of 5 feet.

The key points are that you don't need line of sight for the point of origin, the cube of effect simply expands from that (still no requirements to see the entire cube). Then surfaces in the cube (i.e. the roof/floor) are used to support the web.

• Hello while this answer is correct, it currently lacks the rules support for targetting spells. Jun 15 '19 at 14:27

My inclination here is to say no.

The other replies are showing that you can cast a web while guessing at the anchor points. I have no problem with that--but we have no anchor points here. Attempting to cast it that way will cause it to collapse, I do not believe this is the desired result.

Rather, I think the objective is to lay it across the "floor" (in this case the roof is the floor) and I would say that requires being able to target the it, not merely the creature.