EXHIBIT 10.10 MEMBERSHIP INTEREST SALE AGREEMENT BY AND BETWEEN CLARK/CARR INVESTMENTS, LLC, A MARYLAND LIMITED LIABILITY COMPANY, AS SELLER AND COLUMBIA EQUITY, LP, A VIRGINIA LIMITED PARTNERSHIP, AS PURCHASER TABLE OF CONTENTS

<PAGE>

EXHIBIT 10.10

MEMBERSHIP INTEREST SALE AGREEMENT

BY AND BETWEEN

CLARK/CARR INVESTMENTS, LLC,

A MARYLAND LIMITED LIABILITY COMPANY,

AS SELLER

AND

COLUMBIA EQUITY, LP,

A VIRGINIA LIMITED PARTNERSHIP,

AS PURCHASER

<PAGE>

TABLE OF CONTENTS

<TABLE>

<S> <C>

ARTICLE I THE SALE........................................................................ 3

1.1 Sale of Membership Interest............................................... 3

1.2 Purchase Price............................................................ 3

ARTICLE II REPRESENTATIONS AND COVENANTS.................................................. 4

2.1 Representations by Purchaser.............................................. 4

2.2 Representations by Seller................................................. 5

2.3 Covenants of Purchaser.................................................... 6

2.4 Covenants of Seller....................................................... 6

ARTICLE III CONDITIONS PRECEDENT TO THE CLOSING........................................... 7

3.1 Conditions to Purchaser's Obligations..................................... 7

3.2 Conditions to Seller's Obligations........................................ 7

ARTICLE IV CLOSING AND CLOSING DOCUMENTS.................................................. 8

4.1 Closing................................................................... 8

4.2 Seller's Deliveries....................................................... 8

4.3 Purchaser's Deliveries.................................................... 9

4.4 Fees and Expenses; Closing Costs.......................................... 9

4.5 Adjustments............................................................... 9

ARTICLE V MISCELLANEOUS................................................................... 9

5.1 Notices................................................................... 9

5.2 Entire Agreement; Modifications and Waivers; Cumulative Remedies.......... 10

5.3 Exhibits.................................................................. 10

5.4 Successors and Assigns.................................................... 10

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>

MEMBERSHIP INTEREST SALE AGREEMENT

THIS MEMBERSHIP INTEREST SALE AGREEMENT (this "Agreement") is made as of

this 31st day of January, 2005 by and between Clark/Carr Investments, LLC, a

Maryland limited liability company ("Seller"); and Columbia Equity, LP, a

Virginia limited partnership ("Purchaser").

RECITALS

A. Meadows IV, LLC, a Virginia limited liability company (the "LLC") is

the owner of certain land located in Chantilly, 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 the Meadows IV Building.

B. Meadows IV Investors, LLC, a Virginia limited liability company

("Meadows IV Investors") is the direct and indirect owner of One Hundred and

00/100 percent (100.00%) of the membership interests in the LLC.

C. Seller is the record and beneficial owner of Forty-Three and 60/100

percent (43.60%) of the membership interests in Meadows IV Investors (the

"Membership Interest").

D. Seller desires to sell the Membership Interest to Purchaser, on the

terms and conditions hereinafter set forth.

E. Purchaser desires to purchase the Membership Interest from Seller, 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 SALE

1.1 Sale of Membership Interest. Seller agrees to sell, transfer, assign

and convey the Membership Interest to Purchaser, and Purchaser agrees to

purchase 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 Purchaser 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 Purchase Price. The purchase price (the "Purchase Price") for which

Seller agrees to sell and assign the Membership Interest to Purchaser, and which

Purchaser agrees to pay to Seller, subject to the terms of this Agreement, shall

be equal to an amount providing the Seller with a twenty percent (20%) IRR (as

defined in Meadows IV Investors' Operating Agreement (the "Meadows IV Investors

Operating Agreement")), based on a minimum of a six month investment holding

period for Seller's Capital Contribution (as defined in the Meadows IV

-3-

<PAGE>

Investors Operating Agreement) (that is, based on initial Capital Contribution

of $2,212,500, assuming no distributions by the Company, the minimum Purchase

Price would equal $2,443,176).

ARTICLE II

REPRESENTATIONS AND COVENANTS

2.1 Representations by Purchaser. Purchaser hereby represents and warrants

to Seller 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. Purchaser is duly organized and validly

existing as a limited partnership 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 Purchaser of its

obligations under this Agreement have been duly authorized by all requisite

action of Purchaser and require no further action or approval of Purchaser's

partners or of any other individuals or entities in order to constitute this

Agreement as a binding and enforceable obligation of Purchaser.

(b) Noncontravention. Neither the entry into nor the performance of,

or compliance with, this Agreement by Purchaser has resulted, or will result, in

any violation of, or default under, or result in the acceleration of, any

obligation under the partnership agreement of Purchaser, or any mortgage,

indenture, lien agreement, note, contract, permit, judgment, decree, order,

restrictive covenant, statute, rule, or regulation applicable to Purchaser.

(c) Litigation. There is no action, suit, or proceeding, pending or

known to be threatened, against or affecting Purchaser in any court or before

any arbitrator or before any 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 Purchaser, (iii)

would reasonably be expected to materially and adversely affect the ability of

Purchaser to perform its obligations hereunder, or under any document to be

delivered pursuant hereto.

(d) 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

Purchaser has been obtained.

(e) Bankruptcy with respect to Purchaser. No Act of Bankruptcy has

occurred with respect to Purchaser. 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,

-4-

<PAGE>

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.

(f) Brokerage Commission. Purchaser has not engaged the services of,

nor has it or will it or Seller 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 Purchaser. Purchaser hereby agrees to indemnify and

hold Seller and its employees, directors, members, partners, affiliates and

agents harmless against any actual 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 Seller. Seller hereby represents and warrants unto

Purchaser 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:

(a) Organization and Power. Seller is duly organized, validly

existing, and in good standing as a limited liability company under the laws of

the State of Maryland. Seller 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 Seller of

its obligations hereunder have been duly authorized by all requisite action of

Seller and require no further action or approval of Seller's members or managers

or of any other individuals or entities in order to constitute this Agreement as

a binding and enforceable obligation of Seller.

(b) Noncontravention. To Seller's actual knowledge, neither the

entry into nor the performance of, or compliance with, this Agreement by Seller

has resulted, or will result, in any material violation of, or material default

under, or result in the acceleration of, any material obligation under any

material 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 Seller

or, to the actual knowledge of Seller, to the Membership Interest.

(c) Litigation. There is no action, suit, claim, or proceeding

pending or, to the actual knowledge of Seller, threatened against Seller, or, to

the actual knowledge of Seller, 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) would

reasonably be expected to materially and adversely affect the ability of Seller

to perform its obligations hereunder, or under any document to be delivered

pursuant hereto, (B) would reasonably be expected to create a lien on the

Membership Interest, any part thereof, or any interest therein, or (C) would

reasonably be expected to materially and adversely affect the Membership

Interest, any part thereof, or any interest therein.

(d) Good Title. (A) Seller 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

-5-

<PAGE>

security interests whatsoever (other than the LLC Operating Agreement), and (C)

Sell