The Alexandrian

Justin’s House Rules for OD&D

September 17th, 2011

OD&D - Volume 1: Men & MagicNot quite as auspicious as Gary Gygax’s house rules, but these are the house rules we’ve developed as part of my Thracian Hexcrawl open table campaign.

Virtually all of these rules are the result of discussing the rambling inconsistencies of the rulebooks. For the first five or six sessions of the campaign, in fact, every session started by tackling a few key passages and trying to unravel their meaning (which led to many different experimentations). Over time, however, the table settled sort of naturally into a set of “standard practices”, at which point I codified them and printed up a small booklet to accompany the copies of Volume 1: Men & Magic I have on the table.


One-Handed Weapons: 1d6
Two-Handed Weapons: 2d6, take highest
Light Weapons: 2d6, take lowest

Short Bow: 2d6, take lowest
Long Bow: 1d6
Composite Bow: 2d6, take highest

Light Crossbow: 1d6
Heavy Crossbow: 2d6, take highest

(In OD&D, despite a lengthy list of different weapons all costing varying amounts of money, all attacks do 1d6 points of damage regardless of what weapon you’re using. This always prompted merry discussion. It gave rise to a memorable session in which a character opted, instead of buying a proper weapon, to simply turn 1 gp into 100 cp and then hurl copper pieces for the duration of the session. During this time period I read James Maliszewski’s Dwimmermount Campaign House Rules and mentioned his rule for two-handed weapons (2d6, keep highest). Everyone liked it and we quickly expanded upon the concept.)


Dual-wielding grants you a +1 bonus on your attack roll. On a hit, you deal damage as per the most effective weapon. (You can’t dual-wield with a two-handed weapons unless you have more than two hands.)


Not wearing a helmet inflicts a -1 penalty to Armor Class.

(This was another rule prompted by consideration of the equipment list: Helmets are listed, but what are they good for?)


Shields grant a +1 bonus to Armor Class (as shown on the combat tables) when they are readied. (Surprised characters do not benefit from their shields.) In addition:

Shields Shall Be Splintered:Whenever you take damage, you can opt to have the damage absorbed by your shield. The shield is splintered and destroyed, but you don’t take any damage from the blow.

Magic Shields: You can do the same with a magic shield, but the shield won’t be destroyed. Instead there will be a 75% chance that the shield will lose +1 of its enchantment.

Magic Shields vs.  Spells: In addition, you can automatically sacrifice +1 from a magic shield in order to make a successful save vs. any spell, breath weapon, gaze, or similar effect.

Special Materials:

  • Dragonscale Shields: Can be sacrificed like a magic shield in order to make a successful save vs. any spell, breath weapon, gaze, or similar effect.
  • SilverFaced Shield: Functions as a magic shield against spectral attacks (75% chance of the silver-facing being ruined).

(These rules are adapted from Trollsmyth’s Shields Shall Be Splintered and Aeons ‘n Auguries’ Splintering Shields by Material. Unlike the other house rules here, I included these simply because I liked ’em so much. The result? Unlike the other house rules, these are basically never used.

What I like about all of these house rules, however, is that they provide a simple-yet-effective method of making greatsword wielders (effectively +1 damage), dual-wielders (+1 to hit), and sword-and-boarders (+1 AC plus the splintering) all mechanically diverse and rewarding options.)


1 turn = 10 minutes = 10 rounds = 2 moves
1 segment = 5 minutes = 1 move

1 move = speed x 10 feet
1 turn = 2 moves = speed x 20 feet
1 turn of flight = speed x 40 feet

Search a 10’ wall = 1 full turn
Listening/ESP/Clairvoyance/X-Ray = 1 quarter turn

(Check out Reactions to OD&D: Turns, Rounds, and Segments – Oh My! for a complete description of archaeological text work that was required to piece out this system.)


  • Declare Magic / Preparations
  • Missiles
  • Movement
  • Magic
  • Movement
  • Melee
  • Miscellaneous

All actions in a phase are considered simultaneous. If a character becomes incapacitated in a phase, they will generally not deal damage in that phase.

Surprise: Surprise allows one movement and one action.

Magic: Includes turning and most magic item use. Characters preparing to cast cannot take other actions. Any damage suffered while preparing forces a prime requisite check (modified by damage taken) to avoid losing the spell / turning.

Preparations: Retrieve 1 item, stow a weapon, draw a weapon (while dropping current weapon), pouring oil in front of you.

Missiles: Firing into melee has 50% chance of hitting a random target.

Movement: Move a number of feet equal to your speed (6” = 6 feet) or charge at twice that rate (suffering -2 penalty to AC and attacks for round).

Melee: If you’re engaged in melee, all non-melee actions (spells, missile fire, etc.) are considered a miscellaneous action and delayed until that phase. You cannot attack during melee if you are waiting to take a delayed action in the miscellaneous phase. (A spellcaster forced into melee during the first movement phase can’t cast until the miscellaneous phase, even though they were out of melee when they declared their spell.)

Miscellaneous: Includes helping wounded comrades, imbibing potions, lighting a flask of oil, etc.

Note: It is possible to shoot a missile weapon, move, move again (into melee), make a melee attack, and then drink a potion (although this would require you to be wielding a one-handed missile weapon and a one-handed melee weapon, since you wouldn’t be able to switch weapons between those actions). Similarly, one can declare a spell, cast a spell, move (into melee), and then make a melee attack (but if someone engages you in melee before the spell goes off, your casting is delayed to the miscellaneous phase and the other actions become impossible).


OD&D doesn’t include a system for determining the order in which actions are resolved. My initial impulse was to embrace a system of simultaneous action resolution. We went through several variants of this — generally with a guideline that incapacitation favored the PCs (either striking one last valiant blow before falling unconscious or preventing monsters from dealing damage by slaying them first) — and what I discovered was that I could generally manage the system as long as the number of combatants remained relatively small.

But as group size grew — both due to the popularity of the open table and the increasing number of henchmen and hirelings — it became more difficult to juggle all of the disparate elements into a compelling narrative and game experience. This led to a fresh round of experimentation. Throughout this process I resisted the impulse to simply embrace initiative checks and call it quits (largely because I view my OD&D experiences as a chance to radically experiment with the basic game-form).

I eventually settled on this system, which is largely inspired by the Mmmmmm! System from Swords of Minaria and the Perrin Conventions. Resolution in each phase is simultaneous, but sufficiently broken up that I can manage much larger groups without losing all sense of cohesion and comprehension.

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15 Responses to “Justin’s House Rules for OD&D”

  1. Hautamaki says:

    I like it a lot. Trying to talk my gaming group into going with a much simpler system. Something so simple as to not even really resemble d20 at all. But they are still in love with complexity hehe.

  2. Fabio Milito Pagliara says:

    very very interesting :)

  3. Roger GS says:

    The copper pieces move is classic. But come on, this is OD&D, you’re fully authorized to veto any rules lawyering that goes on …

  4. Joseph says:

    I love the shield rules!

  5. Andrew says:

    These are great.

  6. heromedel says:

    I am definitely going to use some of these. By the way is that a typo on light weapons “1d6 take the lowest” shouldn’t it be 2d6

  7. Justin Alexander says:

    @heromedel: Fixed. Thanks!

    @Roger GS: Why would I veto anything that awesome? :)

    Seriously, though, the guy would spend all his time shaving copper pieces so that they’d have razor-sharp edges. It was such a neat little bit. He was eventually killed when a dire wolverine snatched one of his hurled copper pieces out of the air and jammed it into his trachea.

    Live by the copper piece, die by the copper piece.

  8. Alice of Ebony says:

    Hi – was wondering if you have seen Adventurer Conquerer King?
    Particularly the campaign mode prep and domain level stuff.

  9. Justin Alexander says:

    ACK is on my “I Really Wish I Had Money For This Right Now” list. Definitely looking forward to it.

  10. thibaut says:

    I’m not sure if it’s still relevant to your gaming hobby, but here are some different (and cleaner, i think) house rules i would use for weapons:

    2H = automatic initiative on first round (as in Chainmail, actually)
    2W = +1 to hit and the most efficient weapon hits

    no adjustment for heavy/light weapons except for the original parade rules

    Otherwise, those are great House Rules that you have here. I especially like the shield rules.

  11. David says:

    I have a question about your shield rules. I really like the way it works, but I am worried about the magic shield. Wouldn’t a Magic Shield +0 prevent a character from ever taking damage as it cannot be destroyed?

    Should there be a small chance of destruction, or have I have misunderstood the rule?

  12. Justin Alexander says:

    Magic Shield +0 = that shield isn’t magical any more.

  13. Warclam says:

    Wow, what a chain. I was reading Gm Don’ts 2, which led me to the first part, which led me back here. I’ve been puttering away at making my own system for a while, and this page is rock-solid for giving me ideas.

    I especially love your combat sequence, which looks a lot better than boring old initiative. Having magic and missiles both be delayable by melee, but missiles only if you’re ALREADY in melee while magic can be interrupted by a someone rushing over to stop you, is perfect.

    The part I’m curious about is the second movement phase. Was that added for the benefit of spellcasters, so they’re not totally immobile in a round in which they cast? Obviously it has other consequences like spellcasting tangibly slowing you down, which is neat, but I’m curious about the original motivation.

  14. Justin Alexander says:

    Re: Second movement phase. Basically, yes.

    The opportunity arose because OD&D does this weird thing with movement where you move at twice your movement rate in inches x 10 feet per turn, and then the turn is divided into ten rounds. (IIRC, no explanation is ever given for why movement rates are doubled for movement instead of just assigning a movement rate equal to how far the characters can move in one turn. This is just one of a several weird rules OD&D has when it comes to time and movement.)

    But once you cancel out the “times 10 feet” modifier by dividing the turn into 10 rounds, the only thing you’re left with is the x2 modifier. If you split that into two separate move actions, though, you end up with a really simple “move up to your movement rate in feet per action” thing.

    Having two distinct movement phases goes back to the Perrin Conventions. My major innovation is having these movement phases bracket the Magic phase and using the new “in melee” condition to allow the movement to potentially disrupt the magic. This has a few effects:

    – As you note, it slows spellcasters down without making them completely immobile on a turn where they’re casting.

    – It allows others to lock down the spellcaster by moving into melee. But it limits this to some extent because they still have to be within a SINGLE move of you, not two full moves. (In playtesting, this made a big difference.)

    – It makes spellcasting mechanically distinct from missile fire.

    To put it another way: Being able to disrupt spellcasting is important for balance, and allowing others to take actions while the casting is happening is the easiest way to do that. But we found that allowing the entire round to happen before magic triggered was too punishing.

  15. Rob says:

    Quote: “You can’t dual-wield with a two-handed weapons unless you have more than two hands.”

    Not particularly germane to the discussion at hand, but I love that the game we play requires qualifications like that. :)

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