For a snake, I would say it would depend on how the door is constructed, where the terrarium is located and what is being housed. If it is sliding, then I would expect you could get away with non-tempered, for your kingsnake.
Tempering doubles the breaking strength, and certainly makes it more scratch resistant, amking tempered glass very important for:
1- active lizards
2- large lizards
3- busy locations (where you could accidentally bump something and/or knock something over into the glass)
4- doors where dropping is a possibility (one of our terraria has doors with hinges along the top, so, if we drop that door, instead of gently closing it, we rish breakage with non-tempered glass)
Tempering also increases weight of the glass.
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Justin, Julie and the menagerie...
(Bobbing igs, snapping macklots, exploring ball, hungry kings, hyper grey rat, quacking tribs, hissing roaches, wriggling worms & chirping crickets)
Vermont Herpetological Society Online
www.vermontherps.org