Craft the World Wiki
Inventory Construction

Walls, along with entryways, are blocks used to delimit the boundaries of the shelter.

Walls are all placeable constructions and so, found in game on the third tab of the "Craft" menu (ladder icon), excepting the windows, which are considered "furniture".

Some like the wooden wall can be placed as back and foreground blocks.
Others like the venetian stucco are restricted to the background layer.
And a few like the spire and the roofs are restricted to the foreground layer.