<PAGE>

                                                                   EXHIBIT 10.28

                             CONTRIBUTION AGREEMENT
                                    (KING I)

                                 BY AND BETWEEN

                    CARR CAPITAL REAL ESTATE INVESTMENTS, LLC
                      A VIRGINIA LIMITED LIABILITY COMPANY,

                                 AS CONTRIBUTOR

                                       AND

                              COLUMBIA EQUITY, LP,
                         A VIRGINIA LIMITED PARTNERSHIP,

                                   AS ACQUIRER

<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
<S>                                                                                       <C>
ARTICLE I  THE CONTRIBUTION..........................................................      1

      1.1        Contribution of Membership Interest.................................      1
      1.2        Consideration.......................................................      1
      1.3        Redemption Rights for Units.........................................      2
      1.4        Tax Consequences to Contributor.....................................      2

ARTICLE II  REPRESENTATIONS AND COVENANTS............................................      2

      2.1        Representations by Acquirer.........................................      2
      2.2        Representations by Contributor......................................      3
      2.3        Covenants of Acquirer...............................................      5
      2.4        Covenants of Contributor............................................      6

ARTICLE III  Conditions Precedent to the Closing.....................................      7

      3.1        Conditions to Acquirer's Obligations................................      7
      3.2        Conditions to Contributor's Obligations.............................      7

ARTICLE IV  Closing and Closing Documents............................................      8

      4.1        Closing.............................................................      8
      4.2        Contributor's Deliveries............................................      8
      4.3        Acquirer's Deliveries...............................................      9
      4.4        Fees and Expenses; Closing Costs....................................      9
      4.5        Adjustments.........................................................      9

ARTICLE V  Miscellaneous.............................................................     10

      5.1        Notices.............................................................     10
      5.2        Entire Agreement; Modifications and Waivers; Cumulative Remedies....     10
      5.3        Exhibits............................................................     11
      5.4        Successors and Assigns..............................................     11
      5.5        Article Headings....................................................     11
      5.6        Governing Law.......................................................     11
      5.7        Counterparts........................................................     11
      5.8        Survival............................................................     11
      5.9        Severability........................................................     11
      5.10       Attorneys' Fees.....................................................     11

</TABLE>

EXHIBITS

      A Assignment and Assumption Agreement

<PAGE>

                             CONTRIBUTION AGREEMENT

      THIS CONTRIBUTION AGREEMENT (this "Agreement") is made as of this 31st day
of January, 2005 by and between Carr Capital Real Estate Investments, LLC, a
Virginia limited liability company ("Contributor"); and Columbia Equity, LP, a
Virginia limited partnership ("Acquirer").

                                    RECITALS

      A. King I, LLC, a Virginia limited liability company (the "LLC") is the
owner of certain land located at 1800 Diagonal Road in Alexandria, Virginia (the
"Land") and the office building and related improvements located thereon (the
"Improvements"), which Land and Improvements (collectively, the "Property") are
more commonly known as King Street Station I.

      B. Contributor is the record and beneficial owner of One and 84/100
percent (1.84%) of the membership interests in the LLC (the "Membership
Interest").

      C. Contributor desires to contribute the Membership Interest to Acquirer,
on the terms and conditions hereinafter set forth.

      D. Acquirer desires to acquire the Membership Interest from Contributor,
on the terms and conditions hereinafter set forth.

                                    AGREEMENT

         NOW, THEREFORE, for and in consideration of the mutual covenants herein
contained, the parties hereto agree as follows:

                                   ARTICLE I

                                THE CONTRIBUTION

      1.1 Contribution of Membership Interest. Contributor agrees to contribute,
transfer, assign and convey the Membership Interest to Acquirer, and Acquirer
agrees to acquire and accept transfer of the Membership Interest pursuant to the
terms and conditions set forth in this Agreement. The Membership Interest shall
be transferred to Acquirer free and clear of all liens, encumbrances, security
interests, prior assignments or conveyances, conditions, restrictions, voting
agreements, claims, and any other matters affecting title thereto (other than
the LLC's operating agreement (the "LLC Operating Agreement")).

      1.2 Consideration. The total consideration (the "Consideration") for which
Contributor agrees to contribute and assign the Membership Interest to Acquirer,
and which Acquirer agrees to pay or deliver to Contributor, subject to the terms
of this Agreement, shall be the issuance to Contributor of a number of units of
limited partnership interests in Acquirer ("Units") equal to (a) Seven Hundred
Sixteen Thousand Nine Hundred Thirty-Four Dollars ($716,934), (b) divided by the
price per share at which the common stock, $.01 par value per share, (the
"Common Stock") of Columbia Equity Trust, Inc., a Maryland corporation and the
general partner of Acquirer (the "REIT"), is offered to the public in the
underwritten initial

                                      -1-
<PAGE>

public offering of the Common Stock (the "IPO"). On the Closing Date (as defined
below), the Units shall be issued to Contributor. Upon the request of
Contributor, Acquirer shall issue certificates reflecting Contributor's
ownership of Units. The certificates evidencing the Units will bear appropriate
legends indicating (i) that the Units have not been registered under the
Securities Act of 1933, as amended ("Securities Act"), and (ii) that Acquirer's
Amended and Restated Agreement of Limited Partnership (the "Partnership
Agreement") restricts the transfer of the Units. Upon receipt of the Units and
execution and delivery of the Partnership Agreement, Contributor shall become a
limited partner of Acquirer.

      1.3 Redemption Rights for Units. Each Unit shall be redeemable, at the
option of the holder, in accordance with, but subject to the restrictions
contained in, the Partnership Agreement; provided, however, that such redemption
option may not be exercised prior to the first anniversary of the Closing Date.

      1.4 Tax Consequences to Contributor. Notwithstanding anything to the
contrary contained in this Agreement, including without limitation the use of
words and phrases such as "sell," "sale," purchase," and "pay," the parties
hereto acknowledge and agree that it is their intent that the transaction
contemplated hereby be treated for federal income tax purposes as the
contribution of the Membership Interest by Contributor to Acquirer in exchange
for Units pursuant to Section 721 of the Internal Revenue Code of 1986, as
amended (the "Code"), and not as a transaction in which Contributor is acting
other than in its capacity as a prospective partner of Acquirer.

                                   ARTICLE II
                          REPRESENTATIONS AND COVENANTS

      2.1 Representations by Acquirer. Acquirer hereby represents and warrants
unto Contributor that the following statements are true, correct, and complete
in every material respect as of the date of this Agreement and will be true,
correct, and complete as of the Closing Date:

            (a) Organization and Power. Acquirer is duly organized and validly
existing, under the laws of the Commonwealth of Virginia, and has full right,
power, and authority to enter into this Agreement and to perform all of its
obligations under this Agreement; and, the execution and delivery of this
Agreement and the performance by Acquirer of its obligations under this
Agreement have been duly authorized by all requisite action of Acquirer and
require no further action or approval of Acquirer's partners or of any other
individuals or entities in order to constitute this Agreement as a binding and
enforceable obligation of Acquirer.

            (b) Noncontravention. Neither the entry into nor the performance of,
or compliance with, this Agreement by Acquirer has resulted, or will result, in
any violation of, or default under, or result in the acceleration of, any
obligation under the Partnership Agreement, or any mortgage, indenture, lien
agreement, note, contract, permit, judgment, decree, order, restrictive
covenant, statute, rule, or regulation applicable to Acquirer.

            (c) Litigation. There is no action, suit, or proceeding, pending or
known to be threatened, against or affecting Acquirer in any court or before any
arbitrator or before any

                                      -2-
<PAGE>
federal, state, municipal, or other governmental department, commission, board,
bureau, agency or instrumentality which (i) in any manner raises any question
affecting the validity or enforceability of this Agreement, (ii) would
reasonably be expected to materially and adversely affect the business,
financial position, or results of operations of Acquirer, or (iii) would
reasonably be expected to materially and adversely affect the ability of
Acquirer to perform its obligations hereunder, or under any document to be
delivered pursuant hereto.

            (d) Units Validly Issued. The Units, when issued, will have been
duly and validly authorized and issued, free of any preemptive or similar
rights, and will be fully paid and nonassessable, without any obligation to
restore capital except as required by the Virginia Revised Uniform Limited
Partnership Act (the "Limited Partnership Act"). Upon execution and delivery of
the Partnership Agreement by Contributor, Contributor shall be admitted as a
limited partner of Acquirer as of the Closing Date and shall be entitled to all
of the rights and protections of a limited partner under the Limited Partnership
Act and the provisions of the Partnership Agreement, with the same rights,
preferences, and privileges as all other limited partners on a pari passu basis.

            (e) Consents. Each consent, approval, authorization, order, license,
certificate, permit, registration, designation, or filing by or with any
governmental agency or body necessary for the execution, delivery, and
performance of this Agreement or the transactions contemplated hereby by
Acquirer has been obtained.

            (f) Bankruptcy with respect to Acquirer. No Act of Bankruptcy has
occurred with respect to Acquirer. As used herein, "Act of Bankruptcy" shall
mean if a party hereto shall (A) apply for or consent to the appointment of, or
the taking of possession by, a receiver, custodian, trustee or liquidator of
itself or of all or a substantial part of its property, (B) admit in writing its
inability to pay its debts as they become due, (C) make a general assignment for
the benefit of its creditors, (D) file a voluntary petition or commence a
voluntary case or proceeding under the Federal Bankruptcy Code (as now or
hereafter in effect), (E) be adjudicated bankrupt or insolvent, (F) file a
petition seeking to take advantage of any other law relating to bankruptcy,
insolvency, reorganization, winding-up or composition or adjustment of debts,
(G) fail to controvert in a timely and appropriate manner, or acquiesce in
writing to, any petition filed against it in an involuntary case or proceeding
under the Federal Bankruptcy Code (as now or hereafter in effect), or (H) take
any action for the purpose of effecting any of the foregoing.

            (g) Brokerage Commission. Acquirer has not engaged the services of,
nor has it or will it or Contributor become liable to, any real estate agent,
broker, finder or any other person or entity for any brokerage or finder's fee,
commission or other amount with respect to the transactions described herein on
account of any action by Acquirer. Acquirer hereby agrees to indemnify and hold
Contributor and its employees, directors, members, partners, affiliates and
agents harmless against any claims, liabilities, damages or expenses arising out
of a breach of the foregoing. This indemnification shall survive Closing or any
termination of this Agreement.

      2.2 Representations by Contributor. Contributor hereby represents and
warrants unto Acquirer that each and every one of the following statements is
true, correct, and complete in every material respect as of the date of this
Agreement and will be true, correct, and complete as of the Closing Date:

                                      -3-
<PAGE>

            (a) Organization and Power. Contributor is duly organized, validly
existing, and in good standing as a limited liability company under the laws of
the Commonwealth of Virginia. Contributor has full right, power, and authority
to enter into this Agreement and to assume and perform all of its obligations
under this Agreement; and the execution and delivery of this Agreement and the
performance by Contributor of its obligations hereunder have been duly
authorized by all requisite action of Contributor and require no further action
or approval of Contributor's members or managers or of any other individuals or
entities in order to constitute this Agreement as a binding and enforceable
obligation of Contributor.

            (b) Noncontravention. Neither the entry into nor the performance of,
or compliance with, this Agreement by Contributor has resulted, or will result,
in any violation of, or default under, or result in the acceleration of, any
obligation under any limited liability company agreement, operating agreement,
regulation, mortgage, indenture, lien agreement, note, contract, permit,
judgment, decree, order, restrictive covenant, statute, rule, or regulation
applicable to Contributor or to the Membership Interest.

            (c) Litigation. There is no action, suit, claim, or proceeding
pending or threatened against or affecting Contributor or the Membership
Interest in any court, or before any arbitrator, or before any federal, state,
municipal or other governmental department, commission, board, bureau, agency or
instrumentality which (A) in any manner raises any question affecting the
validity or enforceability of this Agreement, (B) would reasonably be expected
to materially and adversely affect the business, financial position or results
of operations of Contributor, (C) would reasonably be expected to materially and
adversely affect the ability of Contributor to perform its obligations
hereunder, or under any document to be delivered pursuant hereto, (D) would
reasonably be expected to create a lien on the Membership Interest, any part
thereof, or any interest therein, or (E) would reasonably be expected to
adversely affect the Membership Interest, any part thereof, or any interest
therein.

            (d) Good Title. (A) Contributor has good title to the Membership
Interest on the date hereof and will have good title to the Membership Interest
on the Closing Date (other than the LLC Operating Agreement), (B) the Membership
Interest on the date hereof is and on the Closing Date will be free and clear of
all liens, encumbrances, pledges, voting agreements and security interests
whatsoever (other than the LLC Operating Agreement), and (C) Contributor has not
granted any other person or entity an option to purchase or a right of first
refusal upon the Membership Interest nor are there any agreements or
understandings between Contributor and any other person or entity with respect
to the disposition of the Membership Interest (other than the LLC Operating
Agreement).

            (e) No Consents. Each consent, approval, authorization, order,
license, certificate, permit, registration, designation, or filing by or with,
any governmental agency or body necessary of the execution, delivery, and
performance of this Agreement or the transactions contemplated hereby by
Contributor has been obtained or will be obtained on or before the Closing Date.

            (f) Securities Law Matters. (i) In acquiring the Units and engaging
in this transaction, neither Contributor nor any member or shareholder thereof
is relying upon any representations made to it by Acquirer, or any of its
partners, officers, employees, or agents that

                                      -4-
<PAGE>

are not contained herein. Contributor is aware of and understands the risks
involved in investing in the Units and in the Common Stock issuable upon
redemption of such Units. Contributor has had an opportunity to ask questions
of, and to receive answers from, Acquirer and the REIT or a person or persons
authorized to act on their behalf, concerning the terms and conditions of an
investment in the Units and the financial condition, affairs, and business of
Acquirer and the REIT. Contributor confirms that all documents, records, and
information pertaining to its investment in Acquirer that have been requested by
it, have been made available or delivered to Contributor prior to the date
hereof.

                  (ii) Contributor understands that neither the Units nor the
Common Stock issuable upon redemption of the Units have been registered under
the Securities Act or any state securities acts and are instead being offered
and sold in reliance on an exemption from such registration requirements. The
Units issuable to Contributor are being acquired solely for its own account, for
investment, and are not being acquired with a view to, or for resale in
connection with, any distribution, subdivision, or fractionalization thereof, in
violation of such laws, and Contributor does not have any present intention to
enter into any contract, undertaking, agreement, or arrangement with respect to
any such resale. Contributor understands that any certificates representing the
Units will contain appropriate legends reflecting the requirement that the Units
not be resold by Contributor without registration under such laws or the
availability of an exemption from such registration.

            (g) Accredited Investors. Contributor is an accredited investor as
that term is defined in Rule 501 of Regulation D under the Securities Act of
1933, as amended.

            (h) Tax Matters. Contributor represents and warrants that it has
obtained from its own counsel advice regarding the tax consequences of (i) the
transfer of the Membership Interest to Acquirer and the receipt of Units as
consideration therefor, (ii) Contributor's admission as a partner of Acquirer,
and (iii) any other transaction contemplated by this Agreement. Contributor
further represents and warrants that it has not relied on Acquirer or Acquirer's
representatives or counsel for such tax advice.

            (i) Bankruptcy with respect to Contributor. No Act of Bankruptcy has
occurred with respect to Contributor.

            (j) Brokerage Commission. Contributor has not engaged the services
of, nor has it or will it or Acquirer become liable to, any real estate agent,
broker, finder or any other person or entity for any brokerage or finder's fee,
commission or other amount with respect to the transactions described herein on
account of any action by Contributor. Contributor hereby agrees to indemnify and
hold Acquirer and its employees, directors, members, partners, affiliates and
agents harmless against any claims, liabilities, damages or expenses arising out
of a breach of the foregoing. This indemnification shall survive Closing or any
termination of this Agreement.

            (k) Default. To Contributor's actual knowledge, Contributor is not
in default under the LLC Operating Agreement.

      2.3 Covenants of Acquirer. Acquirer agrees as follows:

                                      -5-
<PAGE>

            (a) Further Acts. In addition to the acts, instruments and
agreements recited herein and contemplated to be performed, executed and
delivered by Acquirer and Contributor, Acquirer shall perform, execute, and
deliver or cause to be performed, executed, and delivered at the Closing or
after the Closing, any and all further acts, instruments, and agreements and
provide such further assurances as Contributor may reasonably require to
consummate the transactions contemplated hereunder.

      2.4 Covenants of Contributor. Contributor agrees as follows:

            (a) Actions Regarding Membership Interest. Except as otherwise
permitted hereby, from the date hereof until the Closing Date, Contributor shall
use reasonable commercial efforts not to take any action or fail to take any
action within Contributor's control the result of which would (1) have a
material adverse effect on the Membership Interest, the Property, Contributor's
ability to contribute, transfer, assign and convey the Membership Interest to
Acquirer or Acquirer's ability to continue the ownership thereof after the
Closing Date or (2) cause any of the representations and warranties contained in
Section 2.2 to be untrue as of the Closing Date.

            (b) Confidentiality. Contributor acknowledges that the matters
relating to the REIT, the IPO, this Agreement, and the other documents, terms,
conditions and information related thereto (collectively, the "Information") are
confidential in nature. Therefore, Contributor covenants and agrees to keep the
Information confidential and will not (except as required by applicable law,
regulation or legal process, and only after compliance with the provisions of
this Section 2.4) prior to the IPO, without Acquirer's prior written consent,
disclose any Information in any manner whatsoever; provided, however, that the
Information may be revealed only to Contributor's employees, legal counsel and
financial advisors, each of whom shall be informed of the confidential nature of
the Information. In the event that Contributor or its key employees, legal
counsel or financial advisors (collectively, the "Information Group") are
requested pursuant to, or required by, applicable law, regulation or legal
process to disclose any of the Information, the applicable member of the
Information Group will notify Acquirer promptly so that it may seek a protective
order or other appropriate remedy or, in its sole discretion, waive compliance
with the terms of this Section 2.4. Contributor acknowledges that remedies at
law may be inadequate to protect Acquirer or the REIT against any actual or
threatened breach of this Section 2.4, and, without prejudice to any other
rights and remedies otherwise available, Contributor agrees to the granting of
injunctive relief in favor of the REIT and/or Acquirer without proof of actual
damages. Notwithstanding any other express or implied agreement to the contrary,
the parties agree and acknowledge that each of them and each of their employees,
representatives, and other agents may disclose to any and all persons, without
limitation of any kind, the tax treatment and tax structure of the transaction
and all materials of any kind (including opinions or other tax analyses) that
are provided to any of them relating to such tax treatment and tax structure,
except to the extent that confidentiality is reasonably necessary to comply with
U.S. federal or state securities laws. For purposes of this paragraph, the terms
"tax treatment" and "tax structure" have the meanings specified in Treasury
Regulation section 1.6011-4(c).

            (c) Other Members' Transactions. Contributor, in its capacity as
Manager (as defined in the LLC Operating Agreement), hereby consents to the
assignment by each of the

                                      -6-
<PAGE>

other members of the LLC of such other members' membership interests in the LLC
to Acquirer, and agrees to the admission of Purchaser as a member in the LLC.

            (d) Further Acts. In addition to the acts, instruments and
agreements recited herein and contemplated to be performed, executed and
delivered by Acquirer and Contributor, Contributor shall perform, execute, and
deliver or cause to be performed, executed, and delivered at the Closing or
after the Closing, any and all further acts, instruments, and agreements and
provide such further assurances as Acquirer may reasonably require to consummate
the transactions contemplated hereunder.

                                   ARTICLE III
                       CONDITIONS PRECEDENT TO THE CLOSING

      3.1 Conditions to Acquirer's Obligations. In addition to any other
conditions set forth in this Agreement, Acquirer's obligation to consummate the
Closing is subject to the timely satisfaction of each and every one of the
conditions and requirements set forth in this Section 3.1, all of which shall be
conditions precedent to Acquirer's obligations under this Agreement.

            (a) Contributor's Obligations. Contributor shall have performed all
obligations of Contributor hereunder which are to be performed prior to Closing,
and shall have delivered or caused to be delivered to Acquirer, all of the
documents and other information required of Contributor pursuant to Section 4.2.

            (b) Contributor's Representations and Warranties. Contributor's
representations and warranties set forth in Section 2.2 shall be true and
correct in all material respects as if made again on the Closing Date, and
Contributor shall have executed and delivered to Acquirer at Closing a
certificate to the foregoing effect.

            (c) No Injunction. On the Closing Date, there shall be no effective
injunction, writ, preliminary restraining order or other order issued by a court
of competent jurisdiction restraining or prohibiting the consummation of the
transactions contemplated hereby.

            (d) Completion of IPO. The IPO shall have been completed.

            (e) Other Members Transactions or Aetna Consent. Either (i) all of
the other members of the LLC shall have sold their interests in the LLC to
Acquirer, or (ii) Aetna Life Insurance Company, a Connecticut corporation, and
all other remaining members who have not sold the entirety of their membership
interests in the LLC, shall have consented to the transactions contemplated by
this Agreement.

            (f) Mortgage Holder Consent. The holder of the mortgage loan secured
by the Property (the "Mortgage Holder") shall have consented to the transactions
contemplated by this Agreement.

            (g) Closing. The Closing shall have occurred on or prior to June 30,
2005.

      3.2 Conditions to Contributor's Obligations. In addition to any other
conditions set forth in this Agreement, Contributor's obligation to consummate
the Closing is subject to the

                                      -7-
<PAGE>

timely satisfaction of each and every one of the conditions and requirements set
forth in this Section 3.2, all of which shall be conditions precedent to
Contributor's obligations under this Agreement.

            (a) Acquirer's Obligations. Acquirer shall have performed all
obligations of Acquirer hereunder which are to be performed prior to Closing,
and shall have delivered or caused to be delivered to Contributor, all of the
documents and other information required of Acquirer pursuant to Section 4.3.

            (b) Acquirer's Representations and Warranties. Acquirer's
representations and warranties set forth in Section 2.1 shall be true and
correct in all material respects as if made again on the Closing Date, and
Acquirer shall have executed and delivered to Contributor at Closing a
certificate to the foregoing effect.

            (c) No Injunction. On the Closing Date, there shall be no effective
injunction, writ, preliminary restraining order or other order issued by a court
of competent jurisdiction restraining or prohibiting the consummation of the
transactions contemplated hereby.

            (d) Completion of IPO. The IPO shall have been completed.

            (e) Other Members Transactions or CCREI and Aetna Consent. Either
(i) all of the other members of the LLC shall have sold their interests in the
LLC to Acquirer, or (ii) Carr Capital Real Estate Investments, LLC, a Virginia
limited liability company ("CCREI"), in its capacity as manager of the LLC, and
Aetna Life Insurance Company, a Connecticut corporation, shall have consented to
the transactions contemplated by this Agreement.

            (f) Mortgage Holder Consent. The Mortgage Holder shall have
consented to the transactions contemplated by this Agreement.

            (g) Closing. The Closing shall have occurred on or prior to June 30,
2005.

                                   ARTICLE IV
                          CLOSING AND CLOSING DOCUMENTS

      4.1 Closing. The consummation and closing (the "Closing") of the
transactions contemplated under this Agreement shall take place at the offices
of Hunton & Williams LLP, Washington, D.C., or such other place as is mutually
agreeable to the parties, on the date of the closing of the IPO (the "Closing
Date"), or as otherwise set by agreement of the parties; provided, however, that
this Agreement shall terminate if Closing does not occur prior to June 30, 2005.

      4.2 Contributor's Deliveries. At the Closing, Contributor shall deliver
the following to Acquirer in addition to all other items required to be
delivered to Acquirer by Contributor:

            (a) Assignment of Membership Interest. An Assignment and Assumption
Agreement, in substantially the form of Exhibit A attached hereto (the
"Assignment and Assumption Agreement"), executed by Contributor;

                                      -8-
<PAGE>

            (b) Execution of Partnership Agreement. The signature page of the
Partnership Agreement duly executed by Contributor as a limited partner; and

            (c) Authority Documents. Evidence satisfactory to Acquirer that the
person or persons executing the closing documents on behalf of Contributor has
full right, power, and authority to do so.

            (d) FIRPTA Certificate. An affidavit from Contributor certifying
pursuant to Section 1445 of the Internal Revenue Code that Contributor is not a
foreign corporation, foreign partnership, foreign trust, foreign estate or
foreign person (as those terms are defined in the Internal Revenue Code and the
Income Tax Regulations promulgated thereunder), in form and substance
satisfactory to Acquirer.

            (e) Certificate of Representations and Warranties. The certificate
required by Section 3.1(b).

            (f) Other Documents. Any other document or instrument reasonably
requested by Acquirer or required hereby.

      4.3 Acquirer's Deliveries. At the Closing, Acquirer shall deliver the
following to Contributor:

            (a) Certificates for Units. If certificates are issued, certificates
duly issued by Acquirer in the name of Contributor as of the Closing Date
representing the Units to which Contributor is entitled pursuant to Section 1.2
of this Agreement;

            (b) Assumption of Membership Interest. An Assignment and Assumption
Agreement executed by Acquirer.

            (c) Executed Partnership Agreement. An original of the Partnership
Agreement, duly executed by its general partner; and

            (d) Authority Documents. Evidence satisfactory to Contributor that
the person or persons executing the closing documents on behalf of Acquirer have
full right, power, and authority to do so.

            (e) Certificate of Representations and Warranties. The certificate
required by Section 3.2(b).

            (f) Other Documents. Any other document or instrument reasonably
requested by Contributor or required hereby.

      4.4 Fees and Expenses; Closing Costs. Acquirer shall pay all fees,
expenses and closing costs relating to the transactions contemplated by this
Agreement; provided however, that Contributor shall pay its own attorneys' and
consultants' fees and expenses.

      4.5 Adjustments. Acquirer shall deliver the number Units, whether
certificated or otherwise, to which Contributor is entitled pursuant to Section
1.2 of this Agreement without any

                                      -9-
<PAGE>

setoffs or adjustments. Contributor acknowledges and agrees that no further
distributions will be made from the LLC to its members until the earlier of the
Closing Date or June 30, 2005. At Closing, the Consideration shall be increased
by One and 84/100 percent (1.84%) of the amount, if any, by which all cash held
or for the benefit of the LLC (excluding lender-held reserves, reserves for
leasing and reserves for capital expenditures) exceeds $900,000.

                                    ARTICLE V
                                  MISCELLANEOUS

      5.1 Notices. Any notice provided for by this Agreement and any other
notice, demand, or communication required hereunder shall be in writing and
either delivered in person (including by confirmed facsimile transmission) or
sent by registered or certified mail or overnight courier, return receipt
requested, in a sealed envelope, postage prepaid, and addressed to the party for
which such notice, demand or communication is intended at such party's address
as set forth in this Section. All notices to Acquirer shall be addressed as
follows:

      ACQUIRER:

             Columbia Equity, LP
             c/o Carr Capital Corporation
             1750 H Street, NW, Suite 500
             Washington, DC  20006
             Telephone: (202) 303-3060
             Facsimile: (202) 303-3078
             Attn: Oliver T. Carr, III

Contributor's address for all purposes under this Agreement shall be the
following:

      CONTRIBUTOR:

             Carr Capital Real Estate Investments, LLC
             c/o Carr Capital Corporation
             1750 H Street, NW, Suite 500
             Washington, DC  20006

Any address or name specified above may be changed by a notice given by the
addressee to the other party. Any notice, demand or other communication shall be
deemed given and effective as of the date of delivery in person or receipt set
forth on the return receipt. The inability to deliver because of changed address
of which no notice was given, or rejection or other refusal to accept any
notice, demand or other communication, shall be deemed to be receipt of the
notice, demand or other communication as of the date of such attempt to deliver
or rejection or refusal to accept.

      5.2 Entire Agreement; Modifications and Waivers; Cumulative Remedies. This
Agreement supersedes any existing letter of intent between the parties,
constitutes the entire agreement among the parties hereto and may not be
modified or amended except by instrument in writing signed by the parties
hereto, and no provisions or conditions may be waived other than

                                      -10-
<PAGE>

by a writing signed by the party waiving such provisions or conditions. No delay
or omission in the exercise of any right or remedy accruing to Contributor or
Acquirer upon any breach under this Agreement shall impair such right or remedy
or be construed as a waiver of any such breach theretofore or thereafter
occurring. The waiver by Contributor or Acquirer of any breach of any term,
covenant, or condition herein stated shall not be deemed to be a waiver of any
other breach, or of a subsequent breach of the same or any other term, covenant,
or condition herein contained. All rights, powers, options, or remedies afforded
to Contributor or Acquirer either hereunder or by law shall be cumulative and
not alternative, and the exercise of one right, power, option, or remedy shall
not bar other rights, powers, options, or remedies allowed herein or by law,
unless expressly provided to the contrary herein.

      5.3 Exhibits. All exhibits referred to in this Agreement and attached
hereto are hereby incorporated in this Agreement by reference.

      5.4 Successors and Assigns. Except as set forth in this Article, this
Agreement may not be assigned by Acquirer or Contributor without the prior
approval of the other party hereto. This Agreement shall be binding upon, and
inure to the benefit of, Contributor, Acquirer, and their respective legal
representatives, successors, and permitted assigns.

      5.5 Article Headings. Article headings and article and section numbers are
inserted herein only as a matter of convenience and in no way define, limit, or
prescribe the scope or intent of this Agreement or any part hereof and shall not
be considered in interpreting or construing this Agreement.

      5.6 Governing Law. This Agreement shall be construed and interpreted in
accordance with the laws of the Commonwealth of Virginia, without regard to
conflicts of laws principles.

      5.7 Counterparts. This Agreement may be executed in any number of
counterparts and by any party hereto on a separate counterpart, each of which
when so executed and delivered shall be deemed an original and all of which
taken together shall constitute but one and the same instrument.

      5.8 Survival. All representations and warranties contained in this
Agreement, and all covenants and agreements contained in the Agreement which
contemplate performance after the Closing Date shall survive the Closing.

      5.9 Severability. In case any one or more of the provisions contained in
this Agreement shall for any reason be held to be invalid, illegal, or
unenforceable in any respect, such invalidity, illegality, or unenforceability
shall not affect any other provision hereof, and this Agreement shall be
construed as if such invalid, illegal, or unenforceable provision had never been
contained herein.

      5.10 Attorneys' Fees. Should a party employ an attorney or attorneys to
enforce any of the provisions hereof or to protect its interest in any manner
arising under this Agreement, or to recover damages for breach of this
Agreement, any non-prevailing party in any action pursued in a court of
competent jurisdiction (the finality of which is not legally contested) shall
pay to the

                                      -11-
<PAGE>

prevailing party all reasonable costs, damages, and expenses, including
reasonable attorneys' fees, expended or incurred in connection therewith.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK.]
                     [SIGNATURES APPEAR ON FOLLOWING PAGES.]

                                      -12-
<PAGE>

      IN WITNESS WHEREOF, this Agreement has been entered into effective as of
the date first above written.

                                  CONTRIBUTOR:

                                  Carr Capital Real Estate Investment, LLC, a
                                  Virginia limited liability company

                                  By:      Carr Capital Corporation, a District
                                           of Columbia corporation, its
                                           managing member

                                           By: /s/  Oliver T. Carr, III
                                               ---------------------------------
                                           Name: Oliver T. Carr, III
                                           Title:  President and Chief Executive
                                           Officer

                                  ACQUIRER:

                                  Columbia Equity, LP, a Virginia limited
                                  partnership

                                  By:      Columbia Equity Trust, Inc., a
                                           Maryland corporation, its general
                                           partner

                                           By: /s/  Oliver T. Carr, III
                                               ---------------------------------
                                           Name: Oliver T. Carr, III
                                           Title: Chairman and Chief Executive
                                           Officer

                                      -13-
<PAGE>

                                    EXHIBIT A

                       ASSIGNMENT AND ASSUMPTION AGREEMENT

Carr Capital Real Estate Investments, LLC, a Virginia limited liability company
("Assignor"), for good and valuable consideration paid to the Assignor by
Columbia Equity, LP, a [___________________] ("Assignee"), pursuant to the
Contribution Agreement dated as of ____________, 2005, by and between Assignor
and Assignee (the "Agreement") and for other good and valuable consideration,
the receipt and adequacy of which are hereby acknowledged, does hereby sell,
assign, transfer, convey and deliver to the Assignee, its successors and
assigns, good and indefeasible title to the Membership Interest, free and clear
of all liens, encumbrances, security interests, prior assignments, voting
agreements, conditions, restrictions, pledges, claims, and other matters
affecting title thereto, subject to the LLC Operating Agreement. Assignee does
hereby accept the foregoing Assignment and assumes and agrees to be responsible
for all liabilities and obligations under the LLC Operating Agreement from and
after the date hereof relating to the Membership Interest.

Capitalized terms used but not defined herein shall have the respective meanings
ascribed to them in the Agreement.

IN WITNESS WHEREOF, the parties hereto have caused this Assignment and
Assumption Agreement to be signed by a duly authorized officer of each, this __
day of _____, 2005.

                                  ASSIGNOR:

                                  ______________________________________, a

                                  ______________________________________

                                  By:   _______________________________________
                                  Name: _______________________________________
                                  Title:_______________________________________

                                  ASSIGNEE:

                                  ______________________________________, a

                                  ______________________________________

                                  By:   _______________________________________
                                  Name: _______________________________________
                                  Title:_______________________________________