Is it my or my landlord's responsibility to pay this overly high gas bill?

The gas bill for my apartment was astronomically high this month (it was my first month having lived in the apartment). Upon calling the Philadelphia Gas Works and having an inspector check out the situation, I was told that the reading was correct and that gas was being wasted as a result of thin wall insulation and poor sealing around the windows among other various leaks. The apartment was renovated just before I moved in (there was plaster dust still on the floors on move in day), so clearly the landlord could have corrected these problems during reconstruction. I just looked over my lease, and there are no specific details one way or the other about this sort of issue. That begin said, if and when I bring the matter up to my landlord, is he financially responsible for any of the bill?