40d:Hatch cover

A hatch cover (also called a floor hatch or just hatch) is a circular covering for a hole in the ground, effectively a horizontal door based on the Z-axis. It is classed as furniture and can be built from either rock, wood, metal or glass. When closed, hatches have the symbol ¢, and when open they "disappear", just like doors or floodgates. You can verify the presence of an open hatch by using the k key and moving the cursor over/near the hatch opening. You can also use the t key to view the quality/value of an installed hatch.

When you create any stairway down between two floors, a Floor Hatch, when put on the upper floor, acts exactly like a door. If you lock it, the dwarves will not use that staircase. A closed floor hatch will block the passage of fluids onto the lower floor, and will stop falling creatures. They can also be used on ramps. Up-down stairways do not prevent the use of hatches in that tile to block the down-portion - the up-portion would need to be blocked from the level above that. Floor hatches can also be placed or grouped on open space, provided they have support.

Hatch settings

There are three options one can specify on any door or hatch from the q menu:

• l Forbid/Permit Passage
  • A hatch set to Forbidden is impassable to any dwarves in the game. A hatch cannot be set Forbidden if it is open. Invading thieves may lock-pick and bypass a Forbidden hatch.
• o Keep Tightly Closed/Make Pet-Passable
  • A hatch that is pet-passable allows through traffic of pets. A pet can still pass through a hatch that is tightly closed if it does so while it is being held open by an object or dwarf.
• s Set as Internal/External
  • A hatch set to external functions as a floor when defining boundaries of a room such as a bedroom. A hatch set to internal allows the room boundaries to pour over.

Building Hatches

After constructing a hatch at any of the above workshops, they must be "built" (placed) like all other furniture. Hatches can be built on any free floor tile, over empty space, or on top of down-staircases (or up/down staircases, or even up-staircases, although that last option won't do anything useful). Hatches cannot be placed on the same tile as most other constructions, including all furniture and traps.

To be used effectively, a hatch should either be placed above a downstair (or in an up/down stair) where, like a door, it will impede liquid flow while still allowing access; or alternatively it can be linked up to a lever (and probably placed above a channel, or lava, or below a river etc), which when pulled will temporarily open the hatch, allowing whatever is above to fall down below.

Like grates, hatches placed on top of floor tiles are purely decorative. Placing a hatch cover does not automatically dig out anything under the hatch.

Water which has a hatch on top of it can still be used as a water source and for fishing.

Hatches over empty space can be safely walked on and even driven over by caravans (They do need to be next to a wall or floor for support, however, but they can't even be built if that condition isn't met - and supports on the level below don't do any good ^[Verify]).

On using Hatches

• They work just like doors. Only on the Z-axis.
• The hatch will be flashing if placed over stairs or ramps.
• Trap doors when hooked to pressure plates
• For use over pits and ponds
• Cover for stockpile stashes hidden underground
• Preventing water and magma from flowing down stairs or ramps - useful for aquifer levels
• Last minute defense for an invasion (Mainly for fortress built right into the ground)
• A dwarf falling down a multiple floor stairway will be stopped by a closed floor hatch.
• Hatches can be linked to levers to function like a "vertical" floodgate without blocking liquid accumulating on the surface above - for example they can be used as emergency drains for pools of water - or magma, if made of magma-safe materials.
• Hatches can be deconstructed by creatures with the building destroyer tag, like trolls or cave crocodiles.
• Freezing water has been reported to deconstruct hatches, causing flooding when the water thaws (and leaving the hatch lying nearby the opening).
• Can be used to halt enemies coming from below the hatch, as enemies must be on the same level as their target when making a melee attack. This might not work if an enemy's body temperature is high enough to damage the hatch.

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