Because your house is worth more, your equity and the amount you can borrow are both greater. And you can hire a contractor or do the work yourself. The downside is that loan limits vary by county and tend to be relatively low. The usual term is 30 years. Suppose your home's R-value is the envy of your block.
Utility bills are lower in energy-efficient homes, so the homeowner can afford a bigger loan.
B and C loans. B and C loans are a fallback. While many banks offer them, so do credit unions, brokerage houses and finance companies. You'll also find lenders that push B and C loans for debt consolidation with enticing introductory rates. Total interest and fees tend to be high because of the lenders' added risk.