Page 1

( Mark One ) UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 Form 10 - K or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 1-14315 Delaware ( State or other jurisdiction of incorporation or organization ) CORNERSTONE Cornerstone Building Brands , Inc. ( Exact name of registrant as specified in its charter ) BUILDING BRANDS Title of Each Class Common Stock , $ 0.01 par value 5020 Weston Parkway Suite 400 Cary NC ( Address of principal executive offices ) 76-0127701 ( I.R.S. Employer Identification No. ) 27513 ( Zip Code ) Registrant's telephone number , including area code : ( 866 ) 419-0042 Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol CNR Name of Each Exchange on Which Registered New York Stock Exchange Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes o No ý Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes o No ý Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes ý No o Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes ý No o Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act .