Building stability
The construction system in Valheim implements a stability mechanic to encourage more realistic buildings and drive gameplay. If the player places a building piece that is not sufficiently stable, it will collapse. Stability is primarily dictated by a piece's material, its position and orientation, and the pieces to which it is attached.
Mechanically, the stability of a component is described by a number called its "support". This number is calculated and then checked to determine whether the component should break. A higher support value indicates more stability and less likelihood of breakage.
The support system does not work like it does with real materials and resembles more how pressure propagates in a plumbing system. Or a magic force coming from ground and trees and flowing through the building pieces. For example, there is no limit on how many other pieces a single beam could support.