<PAGE>

                                                                    Exhibit 4.03


                       BUILDING ONE SERVICES CORPORATION
                        10 1/2% Senior Subordinated Note
                                due May 1, 2009

                               CUSIP No._________
                          No.                       $

     BUILDING ONE SERVICES CORPORATION, a Delaware corporation (the "Company",
which term includes any successor corporation), for value received promises to
pay to CEDE & CO. or registered assigns, the principal sum of
on May 1, 2009.

          Interest Payment Dates:  May 1 and November 1, commencing November 1,
1999.

          Record Dates:  April 15 and October 15.

          Reference is made to the furth
er provisions of this Security contained
herein, which will for all purposes have the same effect as if set forth at this
place.

          IN WITNESS WHEREOF, the Company has caused this Security to be signed
manually or by facsimile by its duly authorized officers.

Dated:  April 30, 1999

                              BUILDING ONE SERVICES CORPORATION

                              By:
                                  ----------------------
                                 Name:
                                 Title:

                              By:
                                  ----------------------
                                 Name
                                 Title:
<PAGE>

               [FORM OF TRUSTEE'S CERTIFICATE OF AUTHENTICATION]

          This is one of the 10 1/2% Senior Subordinated Notes due 2009
described in the within-mentioned Indenture.

Dated:  April 30, 1999       IBJ WHITEHALL BANK & TRUST COMPANY,
        as Trustee

                             By:
                                 ----------------------------
                                     Authorized Signatory
<PAGE>

                             (REVERSE OF SECURITY)

                       BUILDING ONE SERVICES CORPORATION

                        10 1/2% Senior Subordinated Note
                                due May 1, 2009

1.  Interest.
    --------

          BUILDING ONE SERVICES CORPORATION, a Delaware corporation (the
"Company"), promises to pay interest on the principal amount of this Security at
the rate per annum shown above.  The Company will pay interest semi-annually on
May 1 and November 1 of each year (the "Interest Payment Date"), commencing
November 1, 1999.  Interest on this Security will accrue from the most recent
date to which interest has been paid or, if no interest has been paid, from
April 30, 1999.  Interest on this Security will be comput
ed on the basis of a
360-day year of twelve 30-day months.

          The Company shall pay interest on overdue principal from time to time
on demand at the rate borne by this Security plus 2% and on overdue installments
of interest (without regard to any applicable grace periods) to the extent
lawful.

2.  Method of Payment.
    -----------------

          The Company shall pay interest on the Securities (except defaulted
interest) to the persons who are the registered Holders at the close of business
on the Record Date immediately preceding the Interest Payment Date even if the
Securities are cancelled on registration of transfer or registration of exchange
after such Record Date.  Holders must surrender Securities to a Paying Agent to
collect principal payments.  The Company shall pay principal and interest in
money of the United States that at the time of payment is legal tender for
payment of public and private debts ("U.S. Legal Tender").  However, the Company
may pay principal and interest by wi
re transfer of Federal funds, or interest by
check payable in such U.S. Legal Tender.  The Company may deliver any such
interest payment to the Paying Agent or to a Holder at the Holder's registered
address.

3.  Paying Agent and Registrar.
    --------------------------

          Initially, IBJ Whitehall Bank & Trust Company (the "Trustee") will act
as Paying Agent and Registrar.  The Company may change any Paying Agent,
Registrar or co-Registrar without notice to the Holders.  The Company or any of
its Subsidiaries may, subject to certain exceptions, act as Registrar or co-
Registrar.

4.  Indenture.
    ---------

          The Company issued the Securities under an Indenture, dated as of
April 30, 1999 (the "Indenture"), among the Company, the Guarantors named
therein and the Trustee.  This Security is one of a duly authorized issue of
Securities of the Company designated as its 10 1/2% Senior
<PAGE>

Subordinated Notes due 2009 (the "Securities"). The Securities are treated as a
single class of securities under the Indenture unless otherwise specified in the
Indenture. Capitalized terms herein are used as defined in the Indenture unless
otherwise defined herein. The terms of the Securities include those stated in
the Indenture and those made part of the Indenture by reference to the Trust
Indenture Act of 1939 (15 U.S.C. (S)(S) 77aaa-77bbbb) (the "TIA"), as in effect
on the date of the Indenture until such time as the Indenture is qualified under
the TIA, and thereafter as in effect on the date on which the Indenture is
qualified under the TIA. Notwithstanding anything to the contrary herein, the
Securities are subject to all such terms, and Holders of
 Securities are referred
to the Indenture and the TIA for a statement of them. The Securities are general
obligations of the Company limited in aggregate principal amount to
$400,000,000.

5.  Subordination.
    -------------

          The Securities are subordinated in right of payment, in the manner and
to the extent set forth in the Indenture, to the prior payment in full in cash
or Cash Equivalents of all Senior Debt of the Company, whether outstanding on
the date of the Indenture or thereafter created, incurred, assumed or
guaranteed.  Each Holder by his acceptance hereof agrees to be bound by such
provisions and authorizes and expressly directs the Trustee, on his behalf, to
take such action as may be necessary or appropriate to effectuate the
subordination provided for in the Indenture and appoints the Trustee his
attorney-in-fact for such purposes.

6.  Optional Redemption.
    -------------------

          The Securities will be redeemable, at the Company's option, in whole
at any time or in
 part from time to time, on and after May 1, 2004, upon not
less than 30 nor more than 60 days' notice, at the following redemption prices
(expressed as percentages of the principal amount) if redeemed during the
twelve-month period commencing on May 1 of the years set forth below, plus, in
each case, accrued and unpaid interest thereon, if any, to the date of
redemption:

      Year                                     Percentage
      ----                                     ----------
      2004                                     105.438%
      2005                                     104.350%
      2006                                     103.263%
      2007                                     102.175%
      2008                                     101.088%
      2009 and thereafter.......               100.000%

7.  Optional Redemption upon Equity Offerings.
    --------------------------------------------

          At any time, or from time to time, on or prior to May 1, 2002, the
Company may, at
its option, use the net cash proceeds of one or more Equity
Offerings to redeem up to 35% aggregate principal amount of the Securities
issued pursuant to the Indenture at a redemption price equal to 110.875% of the
principal amount thereof, plus accrued and unpaid interest thereon, if any, to
the date of redemption; provided that after any such redemption the aggregate
                        --------
principal amount of Securities outstanding must equal at least 65% of the
aggregate principal amount of the Securities issued
<PAGE>

pursuant to the Indenture.  In order to effect the foregoing redemption with the
net cash proceeds of any Equity Offering, the Company shall make such redemption
not more than 90 days after the consummation of any such Equity Offering.

          As used in the preceding paragraph, "Equity Offering" means a public
or private offering of Qualified Capital Stock (other than public offerings with
respect to the Company's Common Stock on Form S-8 or any replacement form for
the Form S-8) of the Company for aggregate net cash proceeds to the Company of
at least $20 million.

8.  Notice of Redemption.
    --------------------

          Notice of redemption will be mailed at least 30 days but not more than
60 days before the Redemption Date to each Holder of Se
curities to be redeemed
at such Holder's registered address.  Securities in denominations of $1,000 may
be redeemed only in whole.  The Trustee may select for redemption portions
(equal to $1,000 or any integral multiple thereof) of the principal of
Securities that have denominations larger than $1,000.

          If any Security is to be redeemed in part only, the notice of
redemption that relates to such Security shall state the portion of the
principal amount thereof to be redeemed.  A new Security in a principal amount
equal to the unredeemed portion thereof will be issued in the name of the Holder
thereof upon cancellation of the original Security.  On and after the Redemption
Date, interest will cease to accrue on Securities or portions thereof called for
redemption.

9.  Change of Control Offer.
    -----------------------

          Upon the occurrence of a Change of Control, the Company will be
required to offer to purchase all of the outstanding Securities at a purchase
price equal to 101% of
the principal amount thereof, plus accrued and unpaid
interest, if any, thereon to the date of repurchase.

10.  Limitation on Asset Sales.
     -------------------------

          The Company is, subject to certain conditions, obligated to make an
offer to purchase Securities at 100% of their principal amount, plus accrued and
unpaid interest, if any, thereon to the date of repurchase with certain net cash
proceeds of certain sales or other dispositions of assets in accordance with the
Indenture.

11.  Denominations; Transfer; Exchange.
     ---------------------------------

          The Securities are in registered form, without coupons, in
denominations of $1,000 and integral multiples of $1,000.  A Holder shall
register the transfer of or exchange Securities in accordance with the
Indenture.  The Registrar may require a Holder, among other things, to furnish
appropriate endorsements and transfer documents and to pay certain transfer
taxes or similar governmental charges payable in connection the
rewith as
permitted by the Indenture.  The Registrar need not register the transfer of or
exchange any Securities or portions thereof selected for redemption, except the
unredeemed portion of any security being redeemed in part.
<PAGE>

12.  Persons Deemed Owners.
     ---------------------

          The registered Holder of a Security shall be treated as the owner of
it for all purposes.

13.  Unclaimed Funds.
     ---------------

          If funds for the payment of principal or interest remain unclaimed for
one year, the Trustee and the Paying Agent will repay the funds to the Company
at its request.  After that, all liability of the Trustee and such Paying Agent
with respect to such funds shall cease.

14.  Discharge Prior to Redemption or Maturity.
     -----------------------------------------

          The Company and the Guarantors may be discharged from their
obligations under the Indenture, the Securities and the Guarantees except for
certain provisions thereof, and may b
e discharged from obligations to comply
with certain covenants contained in the Indenture, the Securities and the
Guarantees, in each case upon satisfaction of certain conditions specified in
the Indenture.

15.  Amendment; Supplement; Waiver.
     -----------------------------

          Subject to certain exceptions, the Indenture, the Securities and the
Guarantees may be amended or supplemented with the written consent of the
Holders of at least a majority in aggregate principal amount of the Securities
then outstanding, and any existing Default or Event of Default or compliance
with any provision may be waived with the consent of the Holders of a majority
in aggregate principal amount of the Securities then outstanding.  Without
notice to or consent of any Holder, the parties thereto may amend or supplement
the Indenture, the Securities and the Guarantees to, among other things, cure
any ambiguity, defect or inconsistency, provide for uncertificated Securities in
addition to or in place of certifica
ted Securities or comply with any
requirements of the Commission in connection with the qualification of the
Indenture under the TIA, or make any other change that does not materially
adversely affect the rights of any Holder of a Security.

16.  Restrictive Covenants.
     ---------------------

          The Indenture contains certain covenants that, among other things,
limit the ability of the Company and its Restricted Subsidiaries to make
restricted payments, to incur indebtedness, to create liens, to sell assets, to
permit restrictions on dividends and other payments by Restricted Subsidiaries
of the Company to the Company, to consolidate, merge or sell all or
substantially all of its assets or to engage in transactions with affiliates.
The limitations are subject to a number of important qualifications and
exceptions.  The Company must annually report to the Trustee on compliance with
such limitations.

17.  Defaults and Remedies.
     ---------------------

          If an Event of Default occu
rs and is continuing, the Trustee or the
Holders of at least 25% in aggregate principal amount of Securities then
outstanding may declare all the Securities to be due and payable immediately in
the manner and with the effect provided in the Indenture.  Holders of
<PAGE>

Securities may not enforce the Indenture, the Securities or the Guarantees
except as provided in the Indenture. The Trustee is not obligated to enforce the
Indenture, the Securities or the Guarantees unless it has received indemnity
satisfactory to it. The Indenture permits, subject to certain limitations
therein provided, Holders of a majority in aggregate principal amount of the
Securities then outstanding to direct the Trustee in its exercise of any trust
or power. The Trustee may withhold from Holders of Securities notice of certain
continuing Defaults or Events of Default if it determines that withholding
notice is in their interest.

18.  Trustee Dealings with Company.
     -----------------------------

          The Trustee under the Indenture, in
 its individual or any other
capacity, may become the owner or pledgee of Securities and may otherwise deal
with the Company, its Subsidiaries or their respective Affiliates as if it were
not the Trustee.

19.  No Recourse Against Others.
     --------------------------

          No stockholder, director, officer, employee or incorporator, as such,
of the Company or any Subsidiary of the Company shall have any liability for any
obligation of the Company under the Securities or the Indenture or for any claim
based on, in respect of or by reason of, such obligations or their creation.
Each Holder of a Security by accepting a Security waives and releases all such
liability.  The waiver and release are part of the consideration for the
issuance of the Securities.

20.  Authentication.
     --------------

          This Security shall not be valid until the Trustee or authenticating
agent signs the certificate of authentication on this Security.

21.  Abbreviations and Defined Terms.
     ----------------
---------------

          Customary abbreviations may be used in the name of a Holder of a
Security or an assignee, such as:  TEN COM (= tenants in common), TEN ENT (=
tenants by the entireties), JT TEN (= joint tenants with right of survivorship
and not as tenants in common), CUST (= Custodian), and U/G/M/A (= Uniform Gifts
to Minors Act).

22.  Governing Law.
     -------------

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

23.  CUSIP Numbers.
     -------------

          Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures, the Company has caused CUSIP numbers to be
printed on the Securities as a convenience to the Holders of the Securities.  No
representation is made as to the accuracy of such
<PAGE>

numbers as printed on the Securities and reliance may be placed only on the
other identification numbers printed hereon.

24.  Indenture.
     ---------

          Each Holder, by accepting a Security, agrees to be bound by all of the
terms and provisions of the Indenture, as the same may be amended from time to
time.  Capitalized terms used herein and not defined herein have the meanings
ascribed thereto in the Indenture.

25.  Guarantees.
     ----------

          This Security will be entitled to the benefits of certain senior
subordinated Guarantees made for the benefit of the Holders.  Reference is
hereby made to the Indenture for a statement of the respective rights,
limitations of rights, duties and obligations thereunder of the Guarantors, the
T
rustee and the Holders.

          The Company will furnish to any Holder of a Security upon written
request and without charge a copy of the Indenture.  Requests may be made to:
BUILDING ONE SERVICES CORPORATION, 800 Connecticut Avenue, NW, Washington, DC
20006, Attention: Office of General Counsel.
<PAGE>

                                ASSIGNMENT FORM

I or we assign and transfer this Security to

_______________________________________________________________

_______________________________________________________________
(Print or type name, address and zip code of assignee or
transferee)

______________________________________________________________________________
(Insert Social Security or other identifying number of assignee or transferee)

and irrevocably appoint _______________________________________ agent to
transfer this Security on the books of the Company.  The agent may substitute
another to act for him.

Dated: _________________    Signed:  _________________________
                                      (Sign exactly as name

                         appears on the other
                                      side of this Security)


Signature Guarantee:  _______________________________________________
                      Participant in a recognized Signature Guarantee Medallion
                      Program (or other signature guarantor program reasonably
                      acceptable to the Trustee)

          In connection with any transfer of this Security occurring prior to
the date which is the earlier of (i) the date of the declaration by the
Commission of the effectiveness of a registration statement under the Securities
Act of 1933, as amended (the "Securities Act") covering resales of this Security
(which effectiveness shall not have been suspended or terminated at the date of
the transfer) and (ii) April 30, 2001 the undersigned confirms that it has not
utilized any general solicitation or general advertising in connection with the
transfer:

                                  [Check One]

            ---------

(1) ___   to the Company or a subsidiary thereof; or

(2) ___   pursuant to and in compliance with Rule 144A under the Securities Act
          of 1933, as amended; or

(3) ___   to an institutional "accredited investor" (as defined in Rule
          501(a)(1), (2), (3) or (7) under the Securities Act of 1933, as
          amended) that has furnished to the Trustee a signed letter containing
          certain representations and agreements (the form of which letter can
          be obtained from the Trustee); or
<PAGE>

(4) ___   outside the United States to a "foreign purchaser" in compliance with
          Rule 904 of Regulation S under the Securities Act of 1933, as amended;
          or

(5) ___   pursuant to the exemption from registration provided by Rule 144 under
          the Securities Act of 1933, as amended; or

(6) ___   pursuant to an effective registration statement under the Securities
          Act of 1933, as amended; or

(7) ___   pursuant to another available exemption from the registration
          statement requirements of the Securities Act of 1933, as amended.

and unless the box below is checked, the undersigned confirms that such Security
is not being transferred to an "affiliate" of the Company as defined in Rule 144
under the Securities Act of
 1933, as amended (an "Affiliate"):

                The transferee is an Affiliate of the Company.

          Unless one of the items is checked, the Trustee will refuse to
register any of the Securities evidenced by this certificate in the name of any
person other than the registered Holder thereof; provided, however, that if item
                                                 --------  -------
(3), (4), (5) or (7) is checked, the Company or the Trustee may require, prior
to registering any such transfer of the Securities, in their sole discretion,
such written legal opinions, certifications (including an investment letter in
the case of box (3) or (4) and other information as the Trustee or the Company
have reasonably requested to confirm that such transfer is being made pursuant
to an exemption from, or in a transaction not subject to, the registration
requirements of the Securities Act of 1933, as amended.

          If none of the foregoing items are checked, the Trustee or Registra
r
shall not be obligated to register this Security in the name of any person other
than the Holder hereof unless and until the conditions to any such transfer of
registration set forth herein and in Section 2.16 of the Indenture shall have
been satisfied.

Dated:                Signed:
      --------------         -----------------------
                             (Sign exactly as name appears on
                             the other side of this Security)

Signature Guarantee:
                    ------------------------------------------------------------



TO BE COMPLETED BY PURCHASER IF (2) ABOVE IS CHECKED

          The undersigned represents and warrants that it is purchasing this
Security for its own account or an account with respect to which it exercises
sole investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act of
1933, as amended, and is aware that the sale to it is being made in reliance on
Ru
le 144A and
<PAGE>

acknowledges that it has received such information regarding the Company as the
undersigned has requested pursuant to Rule 144A or has determined not to request
such information and that it is aware that the transferor is relying upon the
undersigned's foregoing representations in order to claim the exemption from
registration provided by Rule 144A.

Dated:
      ------------------
                                  NOTICE:  To be executed by an executive
                                           officer
<PAGE>

                       OPTION OF HOLDER TO ELECT PURCHASE

          If you want to elect to have this Security purchased by the Company
pursuant to Section 4.15 or Section 4.16 of the Indenture, check the appropriate
box:

Section 4.15 [      ] Section 4.16 [       ]

          If you want to elect to have only part of this Security purchased by
the Company pursuant to Section 4.15 or Section 4.16 of the Indenture, state the
amount:  $___________

Dated: _________________                   Signed:  _________________________
                                                      (Sign exactly as name
                                                      appears on the other
                                                      side of this Security)

Signat
ure Guarantee:   ______________________________________
                       Participant in a recognized Signature Guarantee Medallion
                       Program (or other signature guarantor program reasonably
                       acceptable to the Trustee)