I have a 60 year old home and have made a huge dent in my winter therms and summer AC usage by simply adding some roof insulation and double-layer windows/slidi

I have a 60 year old home and have made a huge dent in my winter therms and summer AC usage by simply adding some roof insulation and double-layer windows/sliding doors a few years ago. Perfect is the enemy of good enough. You are not going to eliminate all gaps.