All buildings used on the farm for housing livestock and the farm family and for storing grain, livestock feed, and farm machinery. In the United States, today's farms are larger, more specialized, and more mechanised than those of the past, and these changes are reflected in the buildings. For example, the two-story barns with haylofts are seldom built any more, in favour of one-story buildings without interior columns and with trussed roofs. The building frames are usually constructed of steel or wood and are covered with prepainted metal sheets. This type of construction is low in cost and has a useful life of about 25 years, which results in a nearly simultaneous wearout and obsolescence of the building. Some buildings have an open front facing the south or east. Others are completely enclosed and insulated so that a warm environment may be maintained to protect young animals or to maximise animal growth and production.