You're right Maj, the second sentence does not take commas:
The house that is on the corner is for sale.
In this case "that is on the corner" is restricting the house to that particular one and no other house. In this case "that" should be used instead of "which". In the first sentence:
Now I understand why my word software keeps underlining my use of which and that. So I won't need use to use mean and threatening language towards it again.