Originally posted by Oakshield:

When it comes to support strength from the ground up:

(strongest support first)

1) Earth walls
2) Stone walls
3) Iron Beams
4) Core Beams
5) Wood Beams.
6) Darkwood Beams.

Yggdrasil wood is only for decorative purposes now. But somehow I have the feeling it'll sooner or later may have some support beams - but still as decoration - as well.

That is wrong, it's more like:

1. Earth
   
2. Iron
   
3. Marble
   
4. Stone
   
5. Core
   
6. Dark
   
7. Wood

And horizontally:

1. Iron
   
2. Core
   
3. Dark
   
4. Wood
   
5. Marble
   
6. Stone
   Impossible: Earth

With marble able to vertically hang slightly, and stone breaking immediately. Horizontal stone is pretty much exclusively arch & floor tiles only.

And Yggdrasil wood makes some specific pieces, spiral staircases are more functional than decorative.