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A Roof over our Heads
Man has three basic needs：food，clothing，and shelter.If a man lives in a warm climate，clothing is not absolutely necessary.However，man cannot live without food，and，he has little chance of survival without shelter.Mankind needs shelter to protect him from the weather，wild animals，insects，and his enemies.
Long before man learned how to build houses，he looked for natural shelters，as the animals did.He found that he could protect himself by climbing up into trees or by crouching under the over-hanging edges of cliffs，or by crawling into caves.The first shelters or homes actually built by man were very simple.For his building materials，he used what he could find easily around him：rocks，tree branches，dried grasses，animal skins.It was a long time，however，before man began to build permanent shelters because，until man learned to farm，he lived by hunting.And，in order to follow game，he had to be able to move from one hunting ground to another.Thus，the first man-made shelters were those that could be easily transported.
The first permanent shelters were probably built twenty to forty thousand years ago by fish eating people who lived in one place as long as the fish supply lasted.Fish-eaters could stay in one place for several years.However，once man learned to farm，he could live longer in one place.Thus，he was able to build a permanent home.Once again，he built his home with the materials he found at hand.In Egypt，for example，wood was scarce，so most houses were built of bricks made of dried mud，with a roof supported by palm tree trunks.
When the Norsemen came from Scandinavia to northern Europe，they found many forests，so they built homes with a framework of heavy tree trunks and they filled the space between the trunks with clay.The Eskimos，on the other hand，lived in a land where there was little or no wood.They learned to adapt their homes perfectly to their surroundings.In the winter time，when everything was covered with snow and ice，the Eskimos built their homes with blocks of ice.When the warm weather came and melted the ice，the Eskimos lived in a tent made of animal skins.
The weather is man’s worst natural enemy.He has to protect himself from extremes of heat and cold and from storms，wind and rain.
Where the weather is hot and dry，the house is generally made of clay brick.The windows are small and high up，so that the heat stays outside.There is often a fiat roof，where people can find a cool place to sleep.In hot，humid areas，on the other hand，people need to be protected from the rain，as well as the heat.In such places，houses are built with wide，overhanging roofs，balconies or verandas （走廊）.
Where there are torrential rains，houses are either built on piles to keep them off the ground，or they have steep thatched （茅草屋顶的）roofs to drain off the rain.People living in the Congo River region have found that steep，heavily-thatched roofs drain off the jungle rains more quickly.Other people in Africa have found that a roof of broad leaves sheds rain quickly.
In Borneo，houses are built on high posts to protect people from dampness.And there are tribes in Malaya who build their homes in the forked branches of trees，and climb up to their houses on bamboo ladders.
In northern countries，people build houses to protect themselves from cold and snow.Their houses are built of sturdy materials，and the roofs are steep，so that the snow will slide off.There are also overhanging eaves （屋檐）to keep the snow from piling up next to the house.And，in northern Siberia，where snowfall is extremely heavy，the roofs even have a funnel-shaped （漏斗状的）platform.to protect the chimneys from drifting snow.