Minecraft wiki entry for Legacy_village_mechanics, associated text: It seems there are three kinds of transparent blocks. First, there are fully transparent blocks such as glass, torches, and fences. Then, there are what are called "partially transparent" blocks such as slabs, stairs, and leaves, which are treated as transparent by the rendering engine. Glowstone is also treated as transparent, although you cannot see through any part of it. Solid transparent blocks can be used as "floor" blocks in villages. Semi-transparent blocks still block light from passing through (at least partially, as is the case with leaves or water), so they're still somehow considered opaque to the lighting engine, which appears to be where it counts. These partially transparent blocks still block the sunlight, and count as roof blocks. Fully transparent blocks still do not count. Water and lava (both flowing and source blocks) are partially transparent, and count as roof blocks. Leaves, slabs, and stairs count as roof blocks.