Cover

From Valheim Wiki

Cover determines when players are sheltered and affects behavior of some structures.

Cover is calculated by checking how many of the 17 cover rays are blocked by obstacles. Each ray starts 0.5 meters from the structure cover point and extends to 29.5 meters (30 meters from the cover point).

Affected How
Player Needs 80% cover and a roof to get the sheltered buff
Workbench Needs 70% cover, and a roof, to craft and repair
Forge Needs 70% cover, and a roof, to craft and repair