I just starte playing minecraft a few days ago and there is one thing really annoying me.

Before I start I know this must have been answered somewhere already, there are thousands of articles written. But I see the game has had some changes and some tricks do not work anymore, that why I choose to ask this myself.


One method I know that kept the spiders away is just simply putting torches on the roof, but I thought it was ugly.

When looking up mod-spawning techniques I thought I could use an inverted technique to keep them away.

I heard that mobs don't spawn on half-blocks or glas, well I thought that would make a great roof. My home is made of wood so I choose a wooden half blocks. I did it like this:

x = wooden half-steps    
O  = glass

x x x x x x x x x x x
x x x x x x x x x x x
x x O O O O O O O x x
x x O O O O O O O x x
x x O O O O O O O x x
x x O O O O O O O x x
x x O O O O O O O x x
x x O O O O O O O x x
x x x x x x x x x x x
x x x x x x x x x x x

The half steps and the glass make for a nice roof. Well lit and it looks good from outside.

Well that night I heard the sound again, I went upstairs, and there was a spider staring at me from the roof.


NOTE: I do not think they spawn and climb on the roof, because when I had the torches on the roof everything was fine. The sides my home are well lit.

  • Are you using a single half step or a double half step? – cedi May 27 '12 at 14:24
  • Just single half-steps. So the glass sticks out above one half. – Saif Bechan May 27 '12 at 14:58

Well, indeed mobs don't spawn on glass or slabs (half-blocks). The way you describe it, that spider couldn't have spawned on the roof. There is not much more to say without actually seeing the house and its surroundings. Is it possible that the spider tracked you from outside and climbed on the roof (unlike other mobs, spiders can track you through walls)? Is it possible that the spider spawned on a nearby cliff or tree and fell on the roof?

  • Ok that could be possible. Today I am doing some redecorating anyway. I will try and place one slab to extend the roof with one slab in all directions, so it sticks out. I guess that way the spider can not come from the sides right?? I am still pretty new, so my house is just a wooden block, 14 x 14 wide. There are no trees or cliffs near. In a 100 x 100 block radius my house is the highest top. – Saif Bechan May 30 '12 at 16:37
  • This is correct, if you build an overhang around the roof, spiders will not be able to climb on it. – Kcats Jun 1 '12 at 5:58
  • Actually, all mobs can track you through walls. Spiders' climbing behaviour just makes it more obvious. – SevenSidedDie Aug 19 '12 at 4:05
  • What I meant is that other mobs will not beeline for you if they can't find an open path to you. Assuming the player is inside the house with the door closed, only spiders will try to get him. – Kcats Aug 20 '12 at 14:40

From Minecraft 1.3.1 you can now place half-slabs on either the top or bottom of a block.

  • If the top of the half-slab is placed at the same height as the top of a full-sized block, then mobs can spawn on it.
  • If the top of the half-slab is half a block high, then no mobs can spawn on it.
  • If you make an overhang on your roof then spiders cannot climb up it.

If the glass on your roof sticks up half a block above those half slabs, your roof should be spawn proof.

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