section_path: Effects on civilization/Structures/Roofs
section_name: Roofs
paragraph_text: Roofs
  
  Snow loads and icings are two principal issues for roofs. Snow loads are related to the climate in which a structure is sited. Icings are usually a result of the building or structure generating heat that melts the snow that is on it.
  
  Snow loads – The Minimum Design Loads for Buildings and Other Structures gives guidance on how to translate the following factors into roof snow loads:
  
  It gives tables for ground snow loads by region and a methodology for computing ground snow loads that may vary with elevation from nearby, measured values. The Eurocode 1 uses similar methodologies, starting with ground snow loads that are tabulated for portions of Europe.
  
  Icings – Roofs must also be designed to avoid ice dams, which result from meltwater running under the snow on the roof and freezing at the eave. Ice dams on roofs form when accumulated snow on a sloping roof melts and flows down the roof, under the insulating blanket of snow, until it reaches below freezing temperature air, typically at the eaves. When the meltwater reaches the freezing air, ice accumulates, forming a dam, and snow that melts later cannot drain properly through the dam. Ice dams may result in damaged building materials or in damage or injury when the ice dam falls off or from attempts to remove ice dams. The melting results from heat passing through the roof under the highly insulating layer of snow.