Mid-1970s

• Starting in the mid-1970s, due to large increases in the price of oil and natural gas, wall insulation in homes became more common. Prior to that time, almost no type of insulation was a common addition when constructing a home because energy costs were far less and the need to save on those costs was almost nonexistent. Chances are good that any home you're living in built before the mid-1970s won't have much insulating material at all.
  
  

Rock Wool

• Thin sheets of rock wool wall insulation first saw use in homes in the early 1950s.Hemera Technologies/AbleStock.com/Getty Images
  
  First commercially produced in 1871, rock wool or stone wool (the names are interchangeable) then became a recognized insulating product. Made of molten rock and sand spun into fibers, it was more appreciated in homes for its sound dampening characteristics. However, prior to the early 1950s, even rock wool normally wouldn't have been applied. And when it was, it would only be a thin sheet of a few inches or so buried in between a home's wall studs.
  
  

Cellulose

• The oldest building insulation material is actually cellulose. It was also made from a variety of materials, which once included old newspapers, cotton, straw and even corncobs. It first saw occasional use in homes in the 1950s. But because energy was cheap then, there'll only be a small amounts placed in a home's walls and attic. Older homes also almost always featured loose-fill cellulose. It most closely resembled shredded paper and was often just simple old newspaper.
  
  

Fiberglass

• Fiberglass insulation was created in 1932 as the result of an accident. By 1953 it had been introduced into automobile manufacturing, but it wouldn't be until the oil and gas price shocks of the 1970s that fiberglass would become common in homes. So if your home was made in the mid-1970s, chances are good you'll find a high level of fiberglass insulation of some form in your walls. There'll be little or none prior to that.
  
  

R-Value

• Wall insulation in older homes was often only a few inches thick if it was there at all.Jupiterimages/Photos.com/Getty Images
  
  In 1945 the measure of effectiveness of an insulating material to resist the transfer of heat was established. Known as R-value, all insulation in older homes possesses lower values in comparison to high R-values found in modern insulation. Rock wool, cellulose and fiberglass, which might be found in older homes, all possess roughly equal R-values of 3.2 per inch. And a few inches will typically be all you'll find in those homes.