@IRonMaN 

I think it's protection against falling airplane parts.

But then, there's this:

Q. Is a roof eligible for the residential energy efficient property tax credit?

A. In general, traditional roofing materials and structural components do not qualify for the credit. However, some solar roofing tiles and solar roofing shingles serve as solar electric collectors while also performing the function of traditional roofing, serving both the functions of solar electric generation and structural support and such items may qualify for the credit. Components such as a roof's decking or rafters that serve only a roofing or structural function do not qualify for the credit.

https://www.irs.gov/newsroom/energy-incentives-for-individuals-residential-property-updated-question...