Weatherization

Was reading a news article on weatherization. It talks about how weatherproofing the houses could save a lot of energy costs and also create lot of jobs! I do agree on the part that it would create jobs and save energy, but I am confused on how it will save money.
Think about it, we go and fix our houses for weatherproofing by spending lot of money (finding charges, service charges and fixing charges!) and then how long will it stay 'weatherproofed'? For a day, a week, a month? The article says if you spend $4000 you could save up to $1000 a year on energy costs. It of course does not talk about the rate at which you might want to recheck/re-weatherproof!
I think, as an economics student, it really does not make economic sense to spend money for weatherproofing (- unless you have a very old house in the first place, in which case weatherproofing would actually be cheaper in a way).

BUT, it sure makes an environment sense!

PS: My personal view anyway :)