MB4 220b: Location of a Lechi (363:8-12)

A lechi made from an Asherah tree is valid (even though it's avodah zarah which is אסור בהנאה).

Even if the lechi is only noticeable from the inside or from the outside alone it is valid.

The lechi has to be within three tefachim of both the wall and the ground.

A lechi doesn't need to be placed with the intent to use it as such as long as it was there before Shabbos.