Walter hired a builder March 1st, 2013 to construct a house for him by July 1st, 2013 for $340,000. At time of contracting, Walter insisted time was of the essence because Walter was selling his old house and had to move out by July 15th. The builder informed Walter in June 2013 that the house could not be completed before September 2013 unless Walter paid an additional fee of $100,000. Walter agreed but later refused to pay the additional sum of money.

Requirement: Is Walter bound to pay the $100,000, why, or why not? Incorporate the facts in your answer. Are there any defenses?