is their a law in texas that states that if a roof decking is a hazard it has to be changed?

http://library7.municode.com/default-test/home.htm?infobase=10123&doc_action=whatsnew
You need a lawyer. Check with a lawyer in your locale to discuss more of the details.

Good luck to you.

God bless.

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Wood shingles are a fire hazard and have been "non-code" in Houston for at least the last 20 years. Depending on the building type, there may be an ordinance violation as well.