JOINDER AGREEMENT

October 12, 2005

Reference is made to the Revolving Credit Agreement, dated as of November 30,
2004 (as from time to time amended and in effect, the “Loan Agreement”), among
First Potomac Realty Investment Limited Partnership (“FPLP”) and each other
Borrower (collectively, the “Borrower”) which from time to time is a party to
the Loan Agreement, KeyBank National Association (“KeyBank”) and the other
lending institutions referred to in the Loan Agreement as Lenders (collectively,
the “Lenders”), and KeyBank, as managing administrative agent for itself and
each other Lender (the “Agent”). Capitalized terms used herein and not otherwise
defined shall have the meanings assigned to such in the Loan Agreement.

In consideration of and as an inducement to the inclusion by the Lenders of each
of the Real Estate Asset(s) identified on Exhibit A hereto as an Eligible
Unencumbered Property pursuant to the Loan Agreement, Gateway Hampton Roads,
LLC, a Virginia limited liability company (the “Additional Borrower”), which is
a Wholly-owned Subsidiary of FPLP, hereby acknowledges and agrees to the terms
and conditions of the Loan Agreement, the Revolving Credit Notes and the other
Loan Documents to which any Borrower is a party, joins in the agreements of the
Borrower under the Loan Agreement, the Revolving Credit Notes and the other Loan
Documents to which any Borrower is a party and agrees that all Obligations of
the Borrower under the Loan Agreement, the Revolving Credit Notes and the other
Loan Documents to which any Borrower is a party shall be the obligations,
jointly and severally, of the Additional Borrower and the Borrower with the same
force and effect as if the Additional Borrower was originally a Borrower under
the Loan Agreement and an original signatory to the Loan Agreement, the
Revolving Credit Notes and the other Loan Documents to which any Borrower is a
party.

The Additional Borrower further agrees that its liability hereunder is direct
and primary and may be enforced by the Lenders and the Agent before or after
proceeding against any other Borrower.

At least three (3) Business Days prior to this Joinder Agreement becoming
effective and each of the Real Estate Asset(s) identified in Exhibit A hereto
becoming an Eligible Unencumbered Property pursuant to the Loan Agreement, the
Additional Borrower shall have delivered to the Agent (with copies to the Agent
for each Lender) the documents and other items required to be delivered pursuant
to Section 8.13(c), 12.2, 12.3, 12.4, 12.8 and 12.13 of the Loan Agreement, in
each case in form and substance satisfactory to the Agent, along with such other
documents, certificates and instruments reasonably required by the Agent,
including, if necessary, updates to the schedules to the Loan Agreement
satisfactory to the Agent. Without in any way limiting the other rights of the
Agent under the Loan Agreement, the Additional Borrower agrees that the Agent
shall have the right to visit and inspect such Eligible Unencumbered Property at
the Borrower’s sole cost and expense.

The undersigned represents and warrants to the Agent and the Lenders that it has
the complete right, power and authority to execute and deliver this Joinder
Agreement and to perform all of the obligations hereunder and the Obligations
under the Loan Agreement, the Revolving Credit Notes and the other Loan
Documents to which any Borrower is a party. This Joinder Agreement shall be
binding upon the undersigned and its successors and assigns and shall inure to
the benefit of the Lenders, the Agent and their respective successors and
assigns.

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Executed as a sealed instrument as of the 12th day of October, 2005.

GATEWAY HAMPTON ROADS, LLC,
a Virginia limited liability company

By: /s/ Barry Bass      
Barry Bass, Executive Vice President and
Chief Financial Officer

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Acknowledged and Agreed:

 
 
FIRST POTOMAC REALTY INVESTMENT LIMITED PARTNERSHIP, for itself and as agent
for each other Borrower
 
By: First Potomac Realty Trust, its
sole general partner
 
By: _/s/ Barry Bass     
 
Barry Bass, Executive Vice President and
Chief Financial Officer

Acknowledged:
KEYBANK NATIONAL ASSOCIATION,
Individually and as Managing Administrative Agent
under the Loan Agreement

By: _John Scott     
Name: John Scott
Title: Vice President

Exhibit A to Joinder Agreement

  1.   2000 Gateway Boulevard, Hampton, VA 23666

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