The Secretary of the Interior’s Standards

The Secretary of the Interior’s Standards for the Treatment of Historic Properties are common sense historic preservation principles in non-technical language. They promote historic preservation best practices that will help to protect our nation’s irreplaceable cultural resources

https://www.nps.gov/tps/standards.htm 

National Parks Service

Technical Preservation Services develops historic preservation standards and guidance on preserving and rehabilitating historic buildings, administers the Federal Historic Preservation Tax Incentives Program for rehabilitating historic buildings, and sets the Secretary of the Interior’s Standards for the Treatment of Historic Properties.

https://www.nps.gov/tps/index.htm