Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

The undersigned hereby certifies, in his capacity as Chief Executive Officer of Modtech Holdings, Inc. (the “Company”), for purposes of 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that based on his knowledge:

• the Quarterly Report of the Company on Form 10-Q for the quarter ended September 30, 2005, (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934; and

• the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: November 9, 2005

/s/    DAVID M. BUCKLEY        

David M. Buckley

Chief Executive Officer