Fehr will earn $3 million over the next two seasons: $1.4 million next season and $1.6 million in 2014-15.
He has eight goals and eight assists in 39 games this season and leads the team with a plus-14 rating.
Chosen by the Capitals with the 18th pick of the 2003 NHL Draft, Fehr has played seven of his eight NHL seasons with Washington. He returned to Washington as a free agent this summer after spending the 2011-12 season with the Winnipeg Jets.
Volpatti will make $1.15 million over the life of his contract: $550,000 in 2013-14 and $600,000 in 2014-15.
The 28-year-old has one assist and seven penalty minutes in 15 games with the Capitals this season. He was acquired on waivers from the Vancouver Canucks on Feb. 28. In 31 games this season, he has one goal, one assist and 33 penalty minutes.