RogerBW's Blog

How to Break a Glass Door 30 May 2021

From a conversation on discussion.tekeli.li came the challenge: if you want to break into someone's house by throwing his plant pots through his (glass) patio doors, how do you go about it? In GURPS, obviously. Do not use this as a guide for actual criminal acts, or if you do at least delete any trace of your having read this post before they catch you.

Let's assume you are not a specialist in these matters so you have no relevant skills; your stats are all a standard 10.

(Case 1)

"Improvised Weapons" (box on p. B404) says that you should find the weapon that most closely resembles the object you're using. (The standard place where I look for pre-calculated examples of improvised weapons is in Martial Arts, but it doesn't help here.) I'm going to regard a flowerpot as a "mace" at -1 (p. B276 Muscle-Powered Ranged Weapon Table); that's probably a bit generous.

So you pick up the pot (a Ready action; if there's distraction I might call for a DX roll to grab it quickly, but probably not), then roll your default Thrown Weapon (Axe/Mace) skill (DX-4, -1 for the weapon). You can make it an All-Out Attack for +1 (the door isn't going to hit back), and you can take three seconds of Aim before you throw to gain the flowerpot's Acc (+1) and a further +2 for the extra time. Range is ×0.5/×1, so you can throw it five yards, but let's assume you're within two yards of the target to avoid range penalties. The door is slightly bigger than a human, so let's assign that a further +1, for a total of 10. All in all you have a 50% chance of hitting the target; this seems rather low.

You then do sw+3 crushing damage, 1d+3 at your average ST 10 (so 3-9 depending on your roll). Ten square feet of plate glass has DR 1 and 3 hit points (p. B558, HP and DR of Structures), so if you do hit you have a ⅚ chance of making a breach in the glass that you can get through. If you get it to -3 hit points it needs to make a HT roll or be destroyed, in which case (being Brittle) it shatters and cannot be repaired. (If the door is larger than that, and it probably is, then the HP you need to shatter the whole thing will increase, but you don't need to do more damage to make a hole in the individual bit you're trying to get through.)

I'd probably give the flowerpot an HT roll to avoid getting cracked.

(Case 2)

If instead you chose to kick the door, you'd be rolling DX-2 to hit (p. 271 Melee Weapon Table; you could also use Brawling or Karate skill if you have them). A melee All-Out Attack gives you +4, and +1 for target size, so you'll hit on a 13- on 3d6 (~84% chance). (If you're using the expanded combat rules from Martial Arts you can also make the attack Telegraphic, since the door won't be parrying it, for a further +4.)

If you do hit, a "Kick w. Boots" does thr+1 damage, net 1d-1 for 0-5 points. If you do 0 or 1 you had no effect; 2-3 will crack the glass a bit but not break it; 4-5 will break a hole that you can go through, as above, but you won't shatter it completely.

Even if you shatter the door, because it did not successfully defend itself, you take no damage from this process.

(Case 3)

Or you could shoulder-charge the door: a Slam (p. B371). Hitting is a straight DX roll, still with the All-Out Attack bonus, so you have a chance of 15- to hit, the best so far (~95%); you might even choose to use All-Out Attack (Strong) rather than (Determined), to trade off that +4 to hit for +2 damage. You do damage dice equal to your HP (10) × speed (5) / 100, so 1d-2, the lowest yet (I suppose one can justify this somewhat because the area of impact is larger than in the other cases). This time the door gets to damage you back, but it has fewer hit points so it rolls 1d-3 against you. If it rolls twice or more what you roll, which is unlikely but possible, you will fall down.

In the worst case you've just taken 3 hit points from bouncing off the door. That's unpleasant, but not a major wound. Even if you're using the optional Bleeding rules (p. B420), it's a crushing injury so you probably won't bleed.

I'll say again what I said in How to Throw a Cat: I would absolutely not stop to do these calculations in a game unless for some reason it mattered exactly how long it took to get through the door (e.g. because there was a horde of zombies shuffling along behind the PCs and I wanted to know how much they'd caught up). Or someone wanted to try to get into a bank vault using their Ten Thousand Dragons Punch. In a mundane situation, I'd just say "OK, there's a plant pot, you smash the door with that" and continue with more interesting things.

No patio doors were harmed during the research for this article. Or flowerpots.

See also:
How to Throw a Cat


  1. Posted by Jon Hancock at 09:40am on 30 May 2021

    I never thought I'd say it, but this doesn't go into enough detail!

    Patio doors are, these days, double-glazed, which means that they are resistant to breaking unless you strike them in the corner. Surely this essential factor needs to be taken into account? 😊

  2. Posted by Chris Bell at 10:30am on 30 May 2021

    I assume the patio door is hardened glass, in which case stop breaking flowerpots against it and go and find a pickaxe.

  3. Posted by John P at 12:17pm on 30 May 2021

    The glass used in doors has to be toughened rather than standard glass (in case that makes a difference).

    But more importantly, if the flower pot fails it's HT check, does it it become a crack pot? Or does that require an insanity check?

    I'll get my coat ...

  4. Posted by Dr Bob at 12:39pm on 30 May 2021

    I'm glad my silly remark about defaulting House Breaking from Gardening provided you with some entertainment.

    I'm pretty sure you or your clothes would take damage from sharp edges of the glass if you shoulder charged it. Glass patio doors - like African Cape Buffalo - are more dangerous after you've damaged them! :-)

  5. Posted by RogerBW at 05:08pm on 30 May 2021

    The standard glass listed on p. B558 is "Glass, plate (1/5” thick)". To thicken it, increase the HP (and perhaps also the DR). I don't believe tempered/toughened glass has been treated in GURPS; there's mention of it in several of the Dungeon Fantasy volumes as a material for weapons and other things (in a suitable magical environment), but no general DR/HP value that I can find.

    And cutting damage from new sharp edges is probably below the resolution of GURPS – though I suspect I'd consider it depending on just how much damage had been done.

  6. Posted by John P at 09:42pm on 30 May 2021

    Remember, after you've put the players through all this, they should find out that the door isn't actually locked anyway.

  7. Posted by RogerBW at 09:48pm on 30 May 2021

    Or there was a key under the flowerpot, but they were too busy aiming it to notice.

  8. Posted by Owen Smith at 02:05pm on 31 May 2021

    You actually have several options for the glass:

    • float glass ie. standard ordinary old window glass. Not legal in a door in the UK for at least 20 years on safety grounds

    • toughened//tempered glass is the minimum legal in the UK for a door now, like the side windows in a car will break into lots of pieces but only if you hit it with a sharp point in the right place. Think those pointed hammers for breaking out of trains or coaches in an accident.

    • laminated glass is what should be the minimum for doors in my view, like the windscreen in a car it is a sandwich of glass, plastic and glass. Very difficult to break and even when it has cracked it's hard to get in through it.

    • bandit proof glass. I don't know what this is, but posh houses in the middle of nowhere tend to have it for patio doors. My dad was offered this last time he had a big floor level window put in.

    Then there is double or triple glazed, it's common for only the outer pane to break.

    And mixtures of glass, my windows are all laminated for the outer pane and toughened for the inner pane. I wish I'd had double laminate, but when I had them put in that was prohibitively expensive for some reason whereas just upgrading the outer pane to laminate was very reasonable priced.

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