40d:Grate

Grates can be placed on a floor or a wall. They allow the passage of water, magma, and projectiles. Dwarves treat grates as floors that can be walked on. To effectively use a floor grate a channel must be dug under it before placement. Grates can be constructed of rock, wood and metals. Grates can also be fished through by Fisherdwarves. Like with a floor, grates prevent the tiles beneath them from being considered outside.

They are represented in game by a: #

They currently cannot be used to cover a large area - grates must be attached orthogonally (ie, not diagonally) to firm ground or some solid construction (a wall, floor, etc), not (just) other grates. Grates left attached only to other grates will deconstruct and collapse.

Grates can be linked to a lever to temporarily make the grate disappear. Liquids can pass through grates in either state, so this is only useful for solid objects (E.g. dwarves).

Grates can be used to filter out large creatures and objects while still allowing liquids through. This is a blessing for areas with underground water sources, as these bodies of water often contain deadly creatures.

Since a grate must be connected to something other than other grates, large areas can only be covered some sort of patchwork, such as this tessellated pattern, which covers 80% of any extended area with grates, and a floor only 1 every 5 tiles:

    +             <- single supporting floor tile
 # #+## #+##
#+####+####+##         + = floor
 ##+####+####+#        # = grate
   ##+####+###
     ##+# ##+#

Compared to Bars

Floor grates and wall grates are much like floor bars and vertical bars. Are they different? Toady writes:

I don't think there's a meaningful distinction at this time [10/31/2007] (perhaps the grate does have that extra step to make the item). Later, I imagine larger items will fall through bars, and only small items will go through grates. Grates might also stop most vermin. Perhaps even small units could go through bars.

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