Core Natural Resources 8-K/A Changes in Registrant's Certifying Accountant

Exhibit 16.1

February 23, 2024

U.S. Securities and Exchange Commission

Office of the Chief Accountant

100 F Street, NE

Washington, DC 20549

Re: Cornerstone Building Brands, Inc.

File No. 1-14315

Dear Sir or Madam:

We have read Item 4.01 of Form 8-K/A of Cornerstone Building Brands, Inc. dated February 23, 2024, and agree with the statements concerning our Firm contained therein.

Very truly yours,

/s/ GRANT THORNTON LLP