EXHIBIT 99.1


                            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 Annual Report of the Company on Form 10-K for the year ended December
     31, 2002 (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: March 31, 2003

                                              /s/ Evan M. Gruber
                                                  --------------
                                              Evan M. Gruber
                                              Chief Executive Officer

This certification accompanies this Report pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002 and shall not be deemed filed by the Company for the
purposes of Section 18 of the Securities Exchange Act of 1934, as amended.