Windows, Barriers, and ... Glass Shields?
By Jason Nelson-Brown

This column provides advice for DMs whose campaigns are in trouble. Do your players constantly bicker or complain about issues both inside and outside of the main campaign action? Do your best ideas fall flat? Have you set up a situation that you now wish you hadn't? Worry no more, because Jason Nelson-Brown has the answers to save your game!

Problem: My Target's Behind a Clear Barrier

I have a question about glass. An NPC is behind a window, and a PC sorcerer moved up to attack. His first thought was to use lesser acid orb, but what about the window -- would [the orb] not hit that first? Then there was a debate about magic missile, hold person, and fireball. Finally the PC just used his crossbow. The DM ruled that the 6 points of damage became 4 (minus 1 for the hardness of the window and minus 1 for the glass HP). Does the window stop line of effect, and as the rules are written, was the DM correct in his call on the damage?

-- Jerald Tripp, from AskWizards.com

At first glance, this is an easy one. The Player's Handbook is quite explicit on p. 176 that "line of effect is canceled by a solid barrier." However flimsy a glass window is (and it's pretty flimsy, with hardness of 1 and 1 hit point per inch), it is nevertheless a solid barrier. Ipso facto, no spell-go-through-o.

By the way, it's probably too late to point out that many medieval 'windows' didn't have glass in them at all, but were more just shuttered casements. If the shutter is open and you can see in, you have a clear shot. Page 176 also states that any gap of 1 square foot or more constitutes an open line of effect, but I digress…

In your case, we have a glass window and an attack through it. The window allows line of sight, obviously, but line of effect is blocked. That means when you are trying to attack someone on the other side, you can't. They have 100% cover from you. What you can do is attack the intervening object in an attempt try to break it. In fact, this is what will happen in the event you shoot in the direction of someone on the other side of the barrier -- your attack strikes the intervening object. Your attack roll cannot be made against the intended target but instead must be made against the window itself. The window is a stationary object, which means it has a base AC of 10, modified by -5 because it has a Dexterity of 0. A typical window is probably size small, giving it a +1 AC bonus for size. Ergo, a window has a base AC of 6. In other words, you almost can't miss it unless you roll a 1, leaving the window intact and you feeling like a tool. But windows don't usually fight back, so you can just keep shooting at it.

The point is that, by the letter of the rules, the attack does not and cannot hit anyone on the inside of the window. By the rules of D&D, the attack on the person you want to shoot (i.e., the person you see in the window) is redirected against the window. You hit it, and unless you make a terrible damage roll, you smash the window. The rest of the damage? It just goes away. This is true if it's a crossbow bolt or a spell that causes physical damage, like acid orb. If the damage is more than the window's hit points, that's just overkill on the window. There is no blow-through to things beyond the window. It's like dropping a foe in melee. It doesn't matter if you just barely drop him negative or if you murderize him by 30 hit points into the negative. The damage does not carry through to the creature behind him, no matter how cinematic that might be (or how many times Legolas shot through multiple targets in the Helm's Deep battle in The Two Towers). The cleave feat lets you emulate this sort of effect in melee -- drop a foe and then slice on through and attack the guy next to him -- but that's still a new attack. You don't get to just apply the overage to the next guy in line. For good or bad, there is no analogous feat for missile weapons or spells.

That means that if your DM intended to follow the rules, he muffed the call, regardless of whether it was a crossbow or a spell. The crossbow hits the window, the window breaks. No damage to anyone inside.

That's the letter of the law. If you want to argue that the rule here is a little out of whack, I might be inclined to agree. We've seen a zillion spy movies where an assassin nails someone through a window with his rifle. Why not let that happen in D&D?

An easy solution to this might be to make it a feat. Maybe something such as "penetrating shot" or "penetrating spell" that lets you cast spells through solid barriers. As long as you have line of sight to the target (which pretty much limits this to paper, glass, and maybe ice, though I could see an application for shooting through a narrow metal grate, thin wooden slats, or even for a cheaterous monster with tremorsense, through a solid stone wall), you can make an attack that blows through the barrier. You apply hardness and the barrier's hit points (and maybe a little extra penalty just because), and the remainder of the damage carries through onto the target. That's basically the way that your DM ruled it. I would close the tremorsense loophole, or else things are going to get very weird and dangerous at high levels. (You need to break through a lot of hit points to burn a spell through solid stone, so maybe even tremorsense isn't that bad.) Other than that, I think I could see it.

Another funny quirk comes up when you think about area-effect attacks. Sure, I can see a glass window intercepting an acid orb -- the window is destroyed, but the acid orb is blocked. I can even see it screening out magic missiles -- the missiles can't get through, and because they can't affect objects, they can't break the window. But what about fireball? Maybe it's the curse of being raised on too many Hollywood action pictures with a million explosions and shattering windows (and yes, I know fireball isn't really an explosion in the rules, no matter how much it looks like one). The rules are explicit that the line of effect for a ranged spell such as fireball has to go to the point of origin of the spell. OK, so the fireball explodes on impact rather than going through the window and exploding inside -- fair enough. But page 175 states that bursts can't affect creatures with total cover, and a glass window provides its 1 hardness, 1 hit point total cover to anyone beyond it. The window will get incinerated, but the spell is instantaneous. It affects everyone in the area of effect at the moment it goes off. At that instant, people behind the window are not in the area of effect. As soon as the window is blasted, they are fair game, but by then the instant is over and so is the spell. The building might be on fire, but no fire damage from the spell goes through the window. That's the rule. If you wanted to rule that blowing up a barrier allowed the burst to continue through, with the stipulation that people behind the barrier get improved cover (see p. 152 in the Player's Handbook), I think that's a pretty reasonable house rule.

As far as spells that have no physical effect, such as hold person, why should a window interfere with them at all? The rules clearly state that the window blocks line of effect (though if there were an open window or door on the other side of the room, and you had range to reach them through that side while you had line of sight to them through your closed-barrier window, you could legally cast against them), but I don't know. I might let it happen. Throw the enchanters a bone once in a while.

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About the Author

Jason Nelson-Brown lives in Seattle with his wife Kelle, daughters Meshia and Indigo, son Allen, and dog Bear. He is an active and committed born-again Christian who began playing D&D in 1981 and currently runs one weekly campaign while playing intermittently in two others.