Older decks made from untreated lumber such as Douglas Fur last about 30 years. Pressure treated lumber last 50 years or longer. Redwood all heart grade or Clear Cedar can last longer than 50 years whereas the less costly knotty grades may last only 40. Hardwoods may last longer than 40 years. Man-made materials come with their own limited warranty which can range anywhere from 25 to 100 years