I think Frenchie's point is valid. The acually time he was spending on his house, he could have been making money. Therefore that potential earnings(minus taxes, commuting, etc.) must be subtracted to figure net savings.
However, some people look at it this way:
Remodeling basement between hours of 7-9pm. Normally watching TV between those hours. Now fixing basement. Therefore saving money.
This is the way people look at it, but it's still wrong because someone could still be working those two hours doing something, and those potential earnings MUST be considered when calculating savings.
Now if Scuba enjoys what he's doing, then great. But his savings is not 80k. It's 80k minus his potential earnings during the time he's working on the house.