My B/X house rules

Simon at …and the sky full of dust. recently mentioned that he uses very few house rules and wondered how unusual this was in the OSR. I commented that I tend to houserule pretty lightly, and I thought I’d expand on that here. Below are the rules and tweaks we’re using at the table for Stonehell on the Borderlands. Some we started with, and others have been adopted and/or amended in the six months since then. I don’t expect anything here to be especially controversial, with the possible exception of my rule for searching, which combines finding traps and detecting secret doors (because they’re both just looking for something hidden) and grants a boon to thieves.

Critical Hits and Fumbles
A natural 20 “to hit” is a critical hit and does maximum damage for the weapon or attack form employed. A natural 1 is a fumble to be interpreted by the DM as circumstances suggest, usually resulting in the character or monster spending a round or two regaining balance, retrieving a lost weapon, or the like. (It’s the roleplaying equivalent of “missing a turn”.)

“Chop When They Drop”
I do what Michael Curtis describes here except that in my game dwarves (belligerent buggers that they are) can do it too.

Unconsciousness and Death
Exactly as described here.

Binding Wounds
Immediately after combat a wounded character may receive “first aid” to restore 1d4-1 hit points lost during that combat. This healing may be administered by the character him- or herself (if conscious!) or by a companion.

Climbing
Any character can try to climb trees, rough walls, cliffs, etc. (Not sheer surfaces, which are the province of the thief.) The chance of success is equal to the character’s chance to Open Doors (i.e., 2 in 6 modified by Strength). Metal armour hampers a climbing character (-2 for chain mail, and -4 for plate). Use of climbing equipment (ropes, crampons, etc.) may grant a bonus.

Searching
Any character may examine an item or area carefully, looking for anything concealed, such as a trap or secret door. This takes a turn (per 10′ x 10′ area). Assuming there is something to find, the chance of finding it is 1 in 6 for most characters, but 2 in 6 for dwarves (due to innate understanding of material construction), elves (superior senses), and thieves (professional training). A thief’s chance improves as the character’s level increases, at the same rate as the ability to Hear Noise (3 in 6 at 3rd level, 4 in 6 at 7th level, 5 in 6 at 11th level). In general, though any character can find traps, only thieves have a chance to disarm them.

Magic-User Spells and Spell Books
First-level magic-users and elves begin play with spell books containing detect magic, read magic, and either (a) one other first-level spell selected by the player, or (b) two determined randomly. Learning a new spell from a spell book requires (in addition to the use of read magic), a number of days of study equal to the spell’s level, at the end of which the player rolls to learn the spell. The chance is 2 in 6 modified by Intelligence. (It’s Open Doors for the mind.)

We originally planned to use Trollsmyth’s popular “Shields Shall Be Splintered” rule because I always thought it sounded like a good ‘un, but in practice neither I nor the players ever remembered it at those dramatic moments when it might have been useful. I decided a house rule that was never used was a house rule too many, so we’ve dropped that one. Maybe another time.