Document:

<PAGE>

                                                                     EXHIBIT 4.3

================================================================================

                      BUILDING ONE SERVICES CORPORATION,
                                  as Issuer,

                     C.R. HIPP CONSTRUCTION COMPANY, INC.,
                        DEL-AIR SERVICE COMPANY, INC.,
                            MH TECHNOLOGIES, INC.,
                            S.L. PAGE CORPORATION,
                           TRI-STATE ELECTRIC, INC.,
                               TRI-STATE, INC.,
                       WALTER C. DAVIS & SON, INC., and

                      the other GUARANTORS named herein,

                                 as Guarantors

                                      AND

                      IBJ WHITEHALL BANK & TRUST COMPANY,

                                  as Trustee

                       _________________________________

                            SUPPLEMENTAL INDENTURE

                         Dated as of  January 31, 2000

                       _________________________________

                                  Relating to
                              up to $400,000,000
                       _________________________________

                  10 1/2% Senior Subordinated Notes due 2009

================================================================================

<PAGE>

                            SUPPLEMENTAL INDENTURE

     This supplemental Indenture (the "Supplemental Indenture") dated as of
January 31, 2000, among C.R. Hipp Construction Company, Inc., Del-Air Service
Company, Inc., MH Technologies, Inc., S.L. Page Corporation, Tri-State Electric,
Inc., Tri-State, Inc. and Walter C. Davis & Son, Inc. (the "New Guarantors"),
companies acquired by BUILDING ONE SERVICES CORPORATION, a Delaware corporation
(the "Company") of wholly owned subsidiaries thereof, since the date of the
Indenture (defined below), the existing subsidiary guarantors listed as
signatories hereto (the "Existing Guarantors") and IBJ Whitehall Bank & Trust
Company, a New York banking corporation, as trustee under the Indenture referred
to below (the "Trustee").

                             W I T N E S S E T H:

     WHEREAS, the Company and the Existing Guarantors have heretofore executed
and delivered to the Trustee an indenture (the "Indenture") dated as of April
30, 1999, providing for the issuance of an aggregate principal amount of up to
$400,000,000 of 10 1/2% Senior Subordinated Notes due 2009 (the "Securities");

     WHEREAS, Section 4.18 of the Indenture provides that under certain
circumstances the Company is required to cause the newly acquired subsidiaries
to execute and deliver to the Trustee a supplemental indenture pursuant to which
such subsidiaries shall unconditionally guarantee all of the Company's
obligations under the Securities on the terms and conditions set forth herein;
and

     WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee, the
Company and the Existing Guarantors are authorized to execute and deliver this
Supplemental Indenture;

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the New
Guarantors, the Company and the Existing Guarantors mutually covenant and agree
for the equal and ratable benefit of the holders of the Securities as follows:

     1. AGREEMENT TO GUARANTEE.  The New Guarantors hereby agree, jointly and
severally with all of the Existing Guarantors, to unconditionally guarantee the
Company's obligations under the Securities on the terms set forth in the
Indenture.

     2. RATIFICATION OF INDENTURE; SUPPLEMENTAL INDENTURE PART OF INDENTURE.
Except as expressly amended hereby, the Indenture is in all respects ratified
and confirmed and all of the terms, conditions and provisions thereof shall
remain in full force and effect.  This Supplemental Indenture shall form a part
of the Indenture for all purposes and every holder of Securities heretofore or
hereafter authenticated and delivered shall be bound hereby.

     3. GOVERNING LAW.  This Supplemental Indenture shall be governed by, and
construed in accordance with, the laws of the State of New York but without
giving effect to applicable principles of conflicts of law to the extent that
the application of the laws of another jurisdiction would be required thereby.

                                      -1-
<PAGE>

     4. TRUSTEE MAKES NO REPRESENTATION.  The recitals contained herein shall be
taken as the statements of the Company and the Trustee assumes no responsibility
for their correctness.  The Trustee makes no representation as to the validity
or sufficiency of this Supplemental Indenture.

     5. COUNTERPARTS.  The parties may sign any number of copies of this
Supplemental Indenture.  Each signed copy shall be an original, but all of them
together represent the same agreement.

     6. EFFECT OF HEADINGS.  The Section headings herein are for convenience
only and shall not effect the construction thereof.

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the date first above written.

                              C.R. HIPP CONSTRUCTION COMPANY, INC.,
                              DEL-AIR SERVICE COMPANY, INC.,
                              MH TECHNOLOGIES, INC.,
                              S.L. PAGE CORPORATION,
                              TRI-STATE ELECTRIC, INC.,
                              TRI-STATE, INC.,
                              WALTER C. DAVIS & SON, INC.
                                   by:

                                   /s/ F. T. BECK
                                   _____________________________
                                   Name:  F. Traynor Beck
                                   Title: Vice President & Assistant Secretary

                              BUILDING ONE SERVICES CORPORATION
                                   by:

                                   /s/ F. T. BECK
                                   _____________________________
                                   Name:  F. Traynor Beck
                                   Title: Executive Vice President

                              ADVENT ELECTRIC CO., INC.
                              AMERICAN AIR CO., INC.
                              BARNES IVEY MECHANICAL COMPANY,
                                L.L.C.
                              BELTLINE MECHANICAL SERVICES, INC.
                              BOXBERGER, INC.
                              BRAZOSPORT MANAGEMENT, INC.
                              BUILDING ONE MECHANICAL SERVICES,
                                INC.
                              BUILDING ONE SERVICE SOLUTIONS, INC.
                              BUYR, INC.

                                      -2-
<PAGE>

                              CHAMBERS ELECTRONIC
                                COMMUNICATIONS, INC.
                              CONSOLIDATED ELECTRICAL GROUP, INC.
                              CRAMAR ELECTRIC, INC.
                              CREST INTERNATIONAL, LLC
                              D/FW MECHANICAL SERVICES, INC.
                              ELECTRICAL DESIGN & CONSTRUCTION,
                                INC.
                              ENGINEERING DESIGN GROUP, INC.
                              FLOR-SHIN, INC.
                              FRED CLARK ELECTRICAL CONTRACTORS,
                                INC.
                              G.S. FINANCIAL, INC.
                              G.S. GROUP, INC.
                              GAMEWELL MECHANICAL, INC.
                              GARFIELD-INDECON ELECTRICAL
                                SERVICES, INC.
                              G.S.I. OF CALIFORNIA, INC.
                              GULF STATES, INC.
                              HUNT ELECTRIC, INC.
                              IVEY MECHANICAL COMPANY, INC.
                              IVEY MECHANICAL SERVICES, L.L.C.
                              LEXINGTON/IVEY MECHANICAL COMPANY,
                                L.L.C.
                              MCINTOSH MECHANICAL, INC.
                              NATIONAL NETWORK SERVICES, INC.
                              OIL CAPITAL ELECTRIC, INC.
                              OMNI MECHANICAL COMPANY
                              OMNI MECHANICAL SERVICES
                              PERIMETER MAINTENANCE CORPORATION
                              POTTER ELECTRIC CO., INC.
                              PRO WIRE SECURITY SYSTEMS, INC.
                              REGENCY ELECTRIC COMPANY ATLANTA
                                OFFICE
                              REGENCY ELECTRIC COMPANY
                                CHARLOTTE OFFICE, INC.
                              REGENCY ELECTRIC COMPANY JACKSONVILLE OFFICE, INC.
                              REGENCY ELECTRIC COMPANY MEMPHIS
                                OFFICE, INC.
                              REGENCY ELECTRIC COMPANY ORLANDO
                                OFFICE, INC.
                              REGENCY ELECTRIC COMPANY PROJECTS
                                GROUP, INC.
                              REGENCY ELECTRIC COMPANY SOUTH
                                FLORIDA, INC.
                              REGENCY ELECTRIC COMPANY, INC.
                              RIVIERA ELECTRIC CONSTRUCTION CO.

                                      -3-
<PAGE>

                              RIVIERA ELECTRIC OF CALIFORNIA, INC.
                              ROBINSON MECHANICAL COMPANY
                              SANDERS BROS., INC.
                              SKC ELECTRIC, INC.
                              SKCE, INC.
                              SPANN BUILDING MAINTENANCE
                                COMPANY
                              SPANN MANAGEMENT GROUP, INC.
                              TAYLOR ELECTRIC, INC.
                              TESS HOLDINGS, INC.
                              TESTRONICS, INC.
                              THE LEWIS COMPANIES, INC.
                              TOWN & COUNTRY ELECTRIC, INC.
                              TRI-CITY ELECTRICAL CONTRACTORS, INC.
                              TRI-M HOLDING CORP.
                              TRI-M CORPORATION
                              TRI-M ELECTRICAL CONSTRUCTION CORP.
                              TRI-M BUILDING AUTOMATION SYSTEMS
                                CORP.
                              TRI-M INFORMATION SYSTEMS CORP.
                              TRI-M INTEGRATED SYSTEMS SOLUTIONS
                                CORP.
                              WALKER ENGINEERING, INC.
                              WARREN ELECTRICAL CONSTRUCTION
                                CORP.
                              WATSON ELECTRICAL CONSTRUCTION CO.
                              WILSON ELECTRIC COMPANY, INC.
                              ELECTRICAL CONTRACTING, INC.
                              MOUNTAIN VIEW ELECTRIC, INC.,
                              B & R ELECTRIC, INC.
                              ATLANTIC ELECTRIC, INC.
                              K & A MECHANICAL, INC.
                              SULLIVAN ELECTRIC, INC.
                                   by

                                   /s/ F. T. BECK
                                   _____________________________
                                   Name:  F. Traynor Beck
                                   Title: Vice President & Assistant Secretary

                              IBJ WHITEHALL BANK & TRUST COMPANY,
                                as Trustee

                                   by

                                      -4-
<PAGE>

                                   /s/ TERENCE RAWLINS
                                   __________________________________
                                   Name:  Terence Rawlins
                                   Title: Vice President

                                      -5-<PAGE>

                                                                     EXHIBIT 4.4
================================================================================

                      BUILDING ONE SERVICES CORPORATION,
                                  as Issuer,

                       GROUP MAINTENANCE AMERICA CORP.,
                    assuming the obligations of Issuer, and

                      the other GUARANTORS named herein,
                                 as Guarantors

                                      AND

                      IBJ WHITEHALL BANK & TRUST COMPANY,

                                  as Trustee

                       _________________________________

                         THIRD SUPPLEMENTAL INDENTURE

                        Dated as of  February 22, 2000

                       ________________________________

                                  Relating to
                              up to $400,000,000
                       _________________________________

                  10 1/2% Senior Subordinated Notes due 2009

================================================================================
<PAGE>

                         THIRD SUPPLEMENTAL INDENTURE

     This Third Supplemental Indenture (the "Supplemental Indenture") dated as
of February 22, 2000, among Building One Services Corporation, a Delaware
corporation (the "Company"), the existing subsidiary guarantors (the "Existing
Guarantors"), Group Maintenance America Corp., a Texas corporation ("GroupMAC"),
GroupMAC's subsidiaries listed on the signature page hereof  (the "New
Guarantors") and IBJ Whitehall Bank & Trust Company, a New York banking
corporation, as trustee under the Indenture referred to below (the "Trustee"),
is entered into in connection with the merger (the "Merger") of the Company with
and into GroupMAC.

                             W I T N E S S E T H:

     WHEREAS, the Company and the Existing Guarantors have heretofore executed
and delivered to the Trustee an indenture (the "Indenture") dated as of April
30, 1999, as supplemented from time to time, providing for the issuance of an
aggregate principal amount of up to $400,000,000 of 10 1/2% Senior Subordinated
Notes due 2009 (the "Securities");

     WHEREAS, the Company has entered into an Agreement and Plan of Merger,
dated November 2, 1999, as amended, whereby the Company has agreed to merge with
and into GroupMAC;

     WHEREAS, Section 5.01 of the Indenture provides that upon a merger of the
Company into another person, such as GroupMAC, GroupMAC is required to execute
and deliver to the Trustee a supplemental indenture pursuant to which GroupMAC
shall unconditionally assume all of the Company's obligations under the
Securities on the terms and conditions set forth in the Indenture;

     WHEREAS, pursuant to Section 4.18 of the Indenture, the New Guarantors are
required to execute and deliver to the Trustee a supplemental indenture pursuant
to which they unconditionally guarantee all of the Company's obligations under
the Securities and the Indenture on the terms set forth in the Indenture; and

     WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee, the
Company, the Existing Guarantors, GroupMAC and the New Guarantors are authorized
to execute and deliver this Supplemental Indenture;

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, it is
hereby mutually covenanted and agreed for the equal and ratable benefit of the
holders of the Securities as follows:

     1.  AGREEMENT TO ASSUME.  GroupMAC hereby assumes the due and punctual
payment of the principal of, and premium, if any, and interest on all of the
Securities and the performance of every covenant of the Securities, the
Indenture and the Registration Rights Agreement, dated as of April 30, 1999,
among the Company, the Guarantors and the Initial Purchasers on the part of the
Company to be performed or observed; provided, however, that such assumption
shall not become effective until the effective time of the Merger;

     2.  AGREEMENT TO GUARANTEE.  The New Guarantors hereby unconditionally
guarantee GroupMAC's obligations under the Securities on the terms set forth in
the Indenture; provided, however, that such guarantee shall not become effective
until the effective time of the Merger.  Notwithstanding the foregoing, this
guarantee shall be automatically and unconditionally released and discharged
(with respect to each of the New Guarantors) upon the terms and conditions
specified in Section 11.04 of the Indenture.
<PAGE>

     3.  SUPPLEMENTAL INDENTURE PART OF INDENTURE.  Except as expressly amended
hereby, all of the terms, conditions and provisions of the Indenture shall
remain in full force and effect.  This Third Supplemental Indenture shall form a
part of the Indenture for all purposes and every holder of Securities heretofore
or hereafter authenticated and delivered shall be bound hereby.

     4.  GOVERNING LAW.  This Third Supplemental Indenture shall be governed by,
and construed in accordance with, the laws of the State of New York but without
giving effect to applicable principles of conflicts of law to the extent that
the application of the laws of another jurisdiction would be required thereby.

     5.  TRUSTEE MAKES NO REPRESENTATION.  The recitals contained herein shall
be taken as the statements of the Company and GroupMAC, and the Trustee assumes
no responsibility for their correctness.  The Trustee makes no representation as
to the validity or sufficiency of this Third Supplemental Indenture.

     6.  COUNTERPARTS.  The parties may sign any number of counterparts of this
Third Supplemental Indenture.  Each signed counterpart shall be an original, but
all of them together represent the same agreement.

     7.  EFFECT OF HEADINGS.  The Section headings herein are for convenience
only and shall not affect the construction thereof.

     IN WITNESS WHEREOF, the parties hereto have caused this Third Supplemental
Indenture to be duly executed as of the date first above written.

                              BUILDING ONE SERVICES CORPORATION

                              By: /s/ F. T. BECK
                                 _______________________________________________
                                    F. Traynor Beck
                                    Executive Vice President

                              Guarantors:

                              ALLIANCE SUPPLY CO., LLC
                              ADVENT ELECTRIC CO., INC.
                              AMERICAN AIR COMPANY., INC.
                              ATLANTIC ELECTRIC COMPANY, INC.
                              B & R ELECTRICAL SERVICES, INC.
                              BARNES IVEY MECHANICAL COMPANY,
                                L.L.C.
                              BELTLINE MECHANICAL SERVICES, INC.
                              BRAZOSPORT MANAGEMENT, INC.
                              BUILDING ONE MECHANICAL SERVICES,
                                INC.
                              BUILDING ONE SERVICE SOLUTIONS, INC.
                              BUYR, INC.
                              C.R. HIPP CONSTRUCTION COMPANY, INC.
                              CHAMBERS ELECTRONIC
                                COMMUNICATIONS, INC.
<PAGE>

                              CONSOLIDATED ELECTRICAL GROUP, INC.
                              CRAMAR ELECTRIC, INC.
                              DEL-AIR SERVICE COMPANY, INC.
                              D/FW MECHANICAL SERVICES, INC.
                              DIVERSIFIED MANAGEMENT SERVICES, U.S.A., INC.
                              EDG POWER GROUP, INC.
                              ELECTRICAL CONTRACTING, INC.

                              ELECTRICAL DESIGN & CONSTRUCTION,
                                INC.
                              ENGINEERING DESIGN GROUP, INC.
                              FRED CLARK ELECTRICAL CONTRACTORS,
                                INC.
                              G.S. FINANCIAL, INC.
                              G.S. GROUP, INC.
                              GAMEWELL MECHANICAL, INC.
                              GARFIELD-INDECON ELECTRICAL
                                SERVICES, INC.
                              G.S.I. OF CALIFORNIA, INC.
                              GULF STATES, INC.
                              HYDRO COOLING, INC.
                              INTERSTATE BUILDING SERVICES, LLC
                              IVEY MECHANICAL COMPANY, INC.
                              IVEY MECHANICAL SERVICES, L.L.C.
                              K & A MECHANICAL, INC.
                              LEXINGTON/IVEY MECHANICAL COMPANY,
                                L.L.C.
                              MH TECHNOLOGIES, INC.
                              MCINTOSH MECHANICAL, INC.
                              NATIONAL NETWORK SERVICES, INC.
                              OIL CAPITAL ELECTRIC, INC.
                              OMNI MECHANICAL COMPANY
                              OMNI MECHANICAL SERVICES
                              POTTER ELECTRIC, INC.
                              PRO WIRE SECURITY SYSTEMS, INC.
                              PROCESS DESIGN BUILDERS, LLC
                              REGENCY ELECTRIC COMPANY ATLANTA
                                OFFICE
                              REGENCY ELECTRIC COMPANY
                                CHARLOTTE OFFICE, INC.
                              REGENCY ELECTRIC COMPANY JACKSONVILLE OFFICE, INC.
                              REGENCY ELECTRIC COMPANY MEMPHIS
                                OFFICE, INC.
                              REGENCY ELECTRIC COMPANY ORLANDO
                                OFFICE, INC.
                              REGENCY ELECTRIC COMPANY PROJECTS
                                GROUP, INC.
                              REGENCY ELECTRIC COMPANY SOUTH
                                FLORIDA, INC.
                              REGENCY ELECTRIC COMPANY, INC.
                              RIVIERA ELECTRIC CONSTRUCTION CO.
<PAGE>

                              RIVIERA ELECTRIC OF CALIFORNIA, INC.
                              ROBINSON MECHANICAL COMPANY
                              SANDERS BROS., INC.
                              SKC ELECTRIC, INC.
                              SKCE, INC.
                              S.L. PAGE CORPORATION
                              SPANN BUILDING MAINTENANCE
                                COMPANY n/k/a BUILDING ONE COMMERCIAL, INC.
                              SULLIVAN ELECTRIC, INC.
                              TAYLOR-HUNT ELECTRIC, INC.
                              TESTRONICS, INC.
                              THE LEWIS COMPANIES, INC.
                              TOWN & COUNTRY ELECTRIC, INC.
                              TRI-CITY ELECTRICAL CONTRACTORS, INC.
                              TRI-M HOLDING CORP.
                              TRI-M CORPORATION
                              TRI-M ELECTRICAL CONSTRUCTION CORP.
                              TRI-M BUILDING AUTOMATION SYSTEMS
                                CORP.
                              TRI-STATE ELECTRIC, INC.
                              TRI-STATE, INC.
                              WALKER ENGINEERING, INC.
                              WATSON ELECTRIC CONSTRUCTION CO.
                              WILSON ELECTRIC COMPANY, INC.
                              WALTER C. DAVIS & SON, INC.
                              ZWART, INC. d/b/a  MOUNTAIN VIEW ELECTRIC, INC.

                              By: /s/ F. T. BECK
                                 _______________________________________________
                                    F. Traynor Beck
                                    Vice President & Assistant Secretary

                              GROUP MAINTENANCE AMERICA CORP.

                              By: /s/ DARREN B. MILLER
                                 _______________________________________________
                                    Darren B. Miller
                                    Executive Vice President

                              Guarantors:

                              A-1 MECHANICAL OF LANSING, INC.
                              AA ADVANCE AIR, INC.
                              A-ABC APPLIANCE, INC.
                              A-ABC SERVICES, INC.
                              A JARL, INC.
                              AIR CONDITIONING ENGINEERS, INC.
<PAGE>

                              AIR CONDITIONING, PLUMBING & HEATING
                              SERVICE CO., INC.
                              AIR SYSTEMS, INC.
                              AIRCON ENERGY INCORPORATED
                              AIRTRON, INC.
                              AIRTRON OF CENTRAL FLORIDA, INC.
                              ALL SERVICE ELECTRIC, INC.
                              ARKANSAS MECHANICAL SERVICES, INC.
                              ATLANTIC INDUSTRIAL CONSTRUCTORS,
                                 INC.
                              CALLAHAN ROACH PRODUCTS &
                                 PUBLICATIONS, INC.
                              CARDINAL CONTRACTING CORPORATION
                              CENTRAL AIR CONDITIONING
                              CONTRACTORS, INC.
                              CENTRAL CAROLINA AIR CONDITIONING
                                 COMPANY
                              CHAPEL ELECTRIC CO.
                              CHARLIE CRAWFORD, INC.
                              CLARK CONVERSE ELECTRIC SERVICE, INC.
                              COLONIAL AIR CONDITIONING COMPANY
                              COMMERCIAL AIR HOLDING COMPANY
                              COMMERCIAL AIR, POWER & CABLE, INC.
                              CONTINENTAL ELECTRICAL     CONSTRUCTION CO.
                              COSTA AND RIHL, INC.
                              COSTA & RIHL PLUMBING, INC.
                              COSTNER BROTHERS, INC.
                              DIVCO, INC.
                              DYNALINK CORPORATION
                              ELECTRICAL ASSOCIATES OF DALLAS, INC.
                              EVANS SERVICES, INC.
                              THE FARFIELD COMPANY
                              FERGUSON ELECTRIC CORPORATION
                              GENTZLER ELECTRICAL CONTRACTORS, INC.
                              GILBERT MECHANICAL CONTRACTORS, INC.
                              GREENWAY INVESTMENT CORP.
                              GROUPMAC FACILITY SERVICES, INC.
                              GROUPMAC HOLDING CORP.
                              GROUPMAC MANAGEMENT CO.
                              GROUPMAC MARYLAND CORP.
                              HPS PLUMBING SERVICES, INC.
                              HALLMARK AIR CONDITIONING, INC.
                              HUNGERFORD MECHANICAL
                                 CORPORATION
                              J.D. STEWARD AIR CONDITIONING, INC.
                              K & N PLUMBING, HEATING AND AIR
                                 CONDITIONING, INC.
                              LANEY'S, INC.
<PAGE>

                              LINFORD SERVICE CO.
                              L. T. MECHANICAL, INC.
                              MACDONALD-MILLER CO., INC.
                              MACDONALD-MILLER INDUSTRIES, INC.
                              MACDONALD-MILLER OF OREGON, INC.
                              MACDONALD-MILLER SERVICE, INC.
                              MASTERS, INC.
                              MECHANICAL INTERIORS, INC.
                              MECHANICAL SERVICES OF ORLANDO, INC.
                              MERRITT ISLAND AIR & HEAT, INC.
                              NEW CONSTRUCTION AIR CONDITIONING,
                                 INC.
                              NORON, INC.
                              PACIFIC RIM MECHANICAL CONTRACTORS,
                                 INC.
                              PAUL E. SMITH CO., INC.
                              PHOENIX ELECTRIC COMPANY
                              RAY AND CLAUDE GOODWIN, INC.
                              RELIABLE MECHANICAL, INC.
                              ROMANOFF ELECTRIC CORP.
                              SEQUOYAH CORPORATION
                              SIBLEY SERVICES, INCORPORATED
                              SNYDER MECHANICAL
                              SOUTHEAST MECHANICAL SERVICE, INC.
                              STATEWIDE HEATING & AIR CONDITIONING,
                                 INC.
                              STEPHEN C. POMEROY, INC.
                              STERLING AIR CONDITIONING, INC.
                              SUN PLUMBING, INC.
                              TEAM MECHANICAL, INC.
                              TOWER ELECTRIC COMPANY
                              TRINITY CONTRACTORS, INC.
                              UNITED ACQUISITION CORP.
                              VALLEY WIDE PLUMBING AND HEATING, INC.
                              VAN'S COMFORTEMP AIR CONDITIONING,
                                 INC.
                              VANTAGE MECHANICAL CONTRACTORS, INC.
                              VERMONT MECHANICAL, INC.
                              WADE'S HEATING & COOLING, INC.
                              WIEGOLD & SONS, INC.
                              WILLIS REFRIGERATION, AIR
                                 CONDITIONING & HEATING, INC.
                              YALE INCORPORATED

                              By: /s/ DARREN B. MILLER
                                 _______________________________________________
                                    Darren B. Miller
                                    Vice President
<PAGE>

                              GROUPMAC INDIANA, LLC

                              By:    AIRTRON, INC.

                                 By: /s/ DARREN B. MILLER
                                    ____________________________________________
                                    Darren B. Miller
                                    Vice President

                              GROUPMAC TEXAS L.P.

                              By:   GROUPMAC HOLDING CORP., general partner

                                 By: /s/ DARREN B. MILLER
                                    _________________________________________
                                    Darren B. Miller
                                    Vice President

                              THE BANK OF NEW YORK, AS SUCCESSOR TO IBJ
                              WHITEHALL BANK & TRUST COMPANY,
                                as Trustee

                              By: /s/ TERENCE RAWLINS
                                 ____________________________________________
                                    Name:  Terence Rawlins
                                    Title: Vice President

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