40d:Grate

Grates can be placed either as walkable platforms (as a floor grate) or as walls (as a wall grate). Creatures treat floor grates as floors that can be walked on for pathing. They allow the passage of water, magma, and archery attacks, and do not block line-of-sight. Floor grates can also be fished through by Fisherdwarves. Like with a hatch cover, grates prevent the tiles beneath them from being considered outside.

Grates can be constructed from stone or ore (with the masonry labour at a mason's workshop), wood (with the carpentry labor in a carpenter's workshop), or metal bars (with the a blacksmithing labour at a forge). They are represented in game by the symbol " # ".

Floor grates must be attached orthogonally (i.e. not diagonally) to firm ground or some solid construction (a wall, floor, etc), not (just) other grates. Constructions, of any type, will not be supported by grates - although the game allows you to designate something supported only by a grate, any construction will collapse as soon as it is completed. Wall grates need only be placed on top of a natural or constructed floor - no supporting walls are needed.

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.

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 objects/creatures.

Since a grate must be connected to something other than other grates, they currently cannot be used to cover a large area by themselves. Therefore, large areas can only be covered with some sort of patchwork connected to solid ground, such as this tessellated pattern, which covers 80% of any extended area with grates, and the top of a "wall" only 1 every 5 tiles:

    +                  <- single supporting tile
 # #+## #+##
#+####+####+##         + = natural ground or top of wall 1 z-level below
 ##+####+####+#        # = grate
   ##+####+###
     ##+# ##+#

Note that none of these are constructed floors, unless those are attached to something other than a 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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