Common elements of Old Dark House pictures are:

1. AN OLD DARK HOUSE
This would seem to go without saying.  It derived from the necessity of stage plays being performed at a central location with a single set.  While the house itself gives identity to each picture, often functioning as a sort of mute character, it also limits each picture – so latter-day viewers like ourselves must be in the mood for static camerawork and repetitive staging.

The houses themselves are usually Gothic Victorian mansions.  The 1930s films tended to respect the houses, but later films (such as THE BLACK CAT, 1941) often denigrated the houses, sometimes having them broken or destroyed at the conclusions.  ONE BODY TOO MANY (1944) modernizes its house by adding an observatory at the top.  Of Course house doesn’t always mean a house.  It could be an Inn or a castle, or a plantation or some other structure where the players mostly congregate.  They may wander around the grounds, but the players still stay near the main structure.

2. SECRET PASSAGES
This includes doors, tunnels, panels, revolving bookcases, you name it.  These passages might lead into a basement or dungeon.  They might (as in SECRET OF THE BLUE ROOM, 1933) even lead away from the house altogether.  Often, a gloved hand might reach out of a secret panel toward an unsuspecting victim.  Again secret passages are not carved in stone, but they are generally accepted as part of the plot.

3. MOTLEY CHARACTERS
Most Old Dark Movies have a large cast of characters, with some characters being very old (like the centenarian patriarch in THE OLD DARK HOUSE, 1932) or very young (with 18-year-old maidens a common type), some being rich, others being poor, some being European, others being American, some being country folk, others being city slickers.  TANGLED DESTINIES (1932) even features a Chinese traveler, treated respectfully by the script.

4. A STRANGE CREATURE
This could be an animal-like creature like a gorilla, bat, or cat.  Or it could be a ghost.  Often, the creature turns out to be a villain in disguise, like on “Scooby-Doo.”  If not a person, the creature may be revealed as a puppet or projection.  HOUSE OF MYSTERY (1934) is rare in featuring both a real gorilla and a guy in a suit.

5. A VOICE FROM THE PAST
This could be a figurative voice, like the words of a Last Will and Testament, or it could be a dire pronouncement from a hidden villain.  The voice (or villain) usually has some connection to a crime or secret or ancestor from a character’s past.  I’ve also seen where it was a person, or character, that comes back from the main character’s past.

6. SCIENCE NOT SORCERY
While a few Old Dark House classics are supernatural, the vast majority ultimately offer a rational scientific explanation for the skullduggery.  In THE PHANTOM (1931), the heroine is threatened not with supernatural terrors but with a brain transplant!

7. LOW BODY COUNT
Don’t expect a bloodbath.  In fact, don’t expect blood.  While virtually every Old Dark House picture includes a murder, few include more than two or three deaths, and fewer still include bloody or gory deaths.  Usually, victims are strangled offscreen.

8. COMIC RELIEF
Bumbling waiters or silly old housekeepers could provide comic relief, or snappy reporters could crack jokes.  Many of the films could be considered more comedic than horrifying.  Later films like William Castle’s OLD DARK HOUSE (named purposefully for the subgenre, 1963) were almost entirely comedic.

9. BAD WEATHER
You can safely bet on some thunder, lightning, rain, or all three to arrive before the movie is out.  ONE FRIGHTENED NIGHT (1935) even opens with a thunderclap.  Quite often the cast of characters are stuck at the Inn, tavern, old dark house because of the weather.