Exhibit 10.20

JOINDER AGREEMENT

THIS JOINDER AGREEMENT (this Agreement),
dated as of February 25, 2011, is entered into by KBSII TWO WESTLAKE PARK, LLC, a Delaware limited liability company (the New Borrower), and WELLS FARGO BANK, NATIONAL ASSOCIATION, as Administrative Agent under that certain
Amended and Restated and Consolidated Loan Agreement, dated as of January 27, 2011 (as the same may be amended, supplemented or otherwise modified from time to time, the Loan Agreement), among KBSII HARTMAN BUSINESS CENTER,
LLC, a Delaware limited liability company, KBSII PLANO BUSINESS PARK, LLC, a Delaware limited liability company, KBSII HORIZON TECH CENTER, LLC, a Delaware limited liability company, KBSII 2500 REGENT BOULEVARD, LLC, a Delaware limited liability
company, KBSII CRESCENT VIII, LLC, a Delaware limited liability company, KBSII NATIONAL CITY TOWER, LLC, a Delaware limited liability company, KBSII GRANITE TOWER, LLC, a Delaware limited liability company, KBSII GATEWAY CORPORATE CENTER, LLC, a
Delaware limited liability company, and KBSII I-81 INDUSTRIAL PORTFOLIO TRUST, a Delaware statutory trust (the Borrowers, each, a Borrower), the Lenders from time to time party thereto and the Administrative
Agent. All capitalized terms used herein and not otherwise defined shall have the meanings set forth in the Loan Agreement.

New Borrower and the Administrative Agent, for the benefit of the Lenders, hereby agree as follows:

Section 1.         Assumption and Joinder.

(a)         The New Borrower hereby expressly assumes, and hereby agrees to perform and observe,
each and every one of the covenants, rights, promises, agreements, terms, conditions, obligations, appointments, duties and liabilities of a Borrower under the Loan Agreement and all of the other Loan Documents applicable to it as a
Borrower under the Loan Agreement. By virtue of the foregoing, the New Borrower hereby accepts and assumes any liability of a Borrower related to each representation, warranty, covenant or obligation made by a Borrower in the Loan Agreement, and
hereby expressly affirms, as of the date hereof, each of such representations, warranties, covenants and obligations.

(b)         All references to the term Borrower in the Loan Agreement or in any
document or instrument executed and delivered or furnished, or to be executed and delivered or furnished, in connection therewith shall be deemed to be a reference to, and shall include, the New Borrower.

Section 2.         Representations and Warranties.   The New Borrower
hereby represents and warrants to the Administrative Agent and the Lenders as follows:

(a)         The New Borrower has the requisite limited liability company power and authority to
enter into this Agreement and to perform its obligations hereunder and under the Loan Agreement and any other Loan Document to which it is a party. The execution, delivery and performance of this Agreement by the New Borrower and the performance of
its obligations under this Agreement, the Loan Agreement, and any other Loan Document have been duly authorized by the sole member of the New Borrower and no other limited liability company proceedings on the part of the New Borrower are necessary
to authorize the execution, delivery or performance of this Agreement, the transactions contemplated hereby or the performance of its obligations under this Agreement, the Loan Agreement or any other Loan Document. This Agreement has been duly
executed and delivered by the New Borrower. This Agreement, the Loan Agreement and each Loan Document constitutes the legal, valid and binding obligation of the New Borrower enforceable against it in accordance with its respective terms, except as
enforceability may be limited by applicable bankruptcy, insolvency, reorganization or similar laws affecting creditors rights generally and by general principles of equity, whether such enforceability is considered in a proceeding at law or in
equity.



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(b)         The representations and warranties set
forth in the Loan Agreement are true and correct in all material respects on and as of the date hereof as such representations and warranties apply to the New Borrower (except to the extent that any such representations and warranties expressly
relate to an earlier date) with the same force and effect as if made on the date hereof.

Section 3.         Security Document.  New Borrower is, simultaneously
with the execution of this Agreement, executing and delivering (i) a Security Document which encumbers certain real property owned by New Borrower and (ii) such other documents and instruments as requested by the Administrative Agent in
accordance with the Loan Agreement. New Borrower acknowledges and agrees that from and after the date of this Agreement, such real property referred to in item (i) of the immediately preceding sentence shall be a Property under the Loan
Agreement.

Section 4.         Further Assurances.  At any time
and from time to time, upon the Administrative Agents request and at the sole expense of the New Borrower, the New Borrower will promptly and duly execute and deliver any and all further instruments and documents and take such further action
as the Administrative Agent reasonably deems necessary to effect the purposes of this Agreement.

Section 5.         Binding Effect.  This Agreement shall be binding upon
the New Borrower and shall inure to the benefit of the Administrative Agent and the other Lenders and their respective successors and assigns.

Section 6.         Counterparts.  This Agreement may be executed in any number of counterparts, each of which when so executed and delivered
shall be an original, but all of which shall constitute one and the same instrument.

Section 7.         Governing Law.  This Agreement shall be governed by,
and construed and enforced in accordance with the laws of the State of California, except to the extent preempted by federal laws.

Section 8.         JURY TRIAL WAIVER.  TO THE EXTENT PERMITTED BY THEN APPLICABLE LAW, EACH PARTY TO THIS AGREEMENT HEREBY EXPRESSLY WAIVES
ANY RIGHT TO TRIAL BY JURY OF ANY CLAIM, DEMAND, ACTION OR CAUSE OF ACTION (a) ARISING UNDER THE LOAN DOCUMENTS OR OTHER RELATED DOCUMENTS, INCLUDING, WITHOUT LIMITATION, ANY PRESENT OR FUTURE MODIFICATION THEREOF OR (b) IN ANY WAY
CONNECTED WITH OR RELATED OR INCIDENTAL TO THE DEALINGS OF THE PARTIES HERETO OR ANY OF THEM WITH RESPECT TO THE LOAN DOCUMENTS OR OTHER RELATED DOCUMENTS (AS NOW OR HEREAFTER MODIFIED) OR ANY OTHER INSTRUMENT, DOCUMENT OR AGREEMENT EXECUTED OR
DELIVERED IN CONNECTION HEREWITH, OR THE TRANSACTIONS RELATED HERETO OR THERETO, IN EACH CASE WHETHER SUCH CLAIM, DEMAND, ACTION OR CAUSE OF ACTION IS NOW EXISTING OR HEREAFTER ARISING, AND WHETHER SOUNDING IN CONTRACT OR TORT OR OTHERWISE; AND EACH
PARTY HEREBY AGREES AND CONSENTS THAT ANY PARTY TO THIS AGREEMENT MAY FILE AN ORIGINAL COUNTERPART OR A COPY OF THIS SECTION WITH ANY COURT AS WRITTEN EVIDENCE OF THE CONSENT OF THE PARTIES HERETO TO THE WAIVER OF ANY RIGHT THEY MIGHT OTHERWISE HAVE
TO TRIAL BY JURY.

Section 9.         Limitations on Personal
Liability.  The limitations on personal liability of the shareholders, partners and members of the Borrowers contained in Section 13.27 of the Loan Agreement shall apply to this.

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IN WITNESS WHEREOF, New Borrower has caused this Agreement to be duly executed by its
respective authorized officer, and the Administrative Agent, for the benefit of the Lenders, has caused the same to be accepted by its authorized officer, as of the day and year first above written.

New Borrower

KBSII TWO WESTLAKE
PARK, LLC,

a Delaware limited liability company



|    |  |                                                      |  |                                                      |  |                                                |  |                                            |  |                                                  |  | 
|--- |  | ---------------------------------------------------- |  | ---------------------------------------------------- |  | ---------------------------------------------- |  | ------------------------------------------ |  | ------------------------------------------------ |  | 
|By: |  | KBSII REIT ACQUISITION XXII, LLC,                   
|    |  | a Delaware limited liability company,its sole member
|    |  |                                                     
|    |  | By:                                                  |  | KBS REIT PROPERTIES II, LLC,                        
|    |  |                                                      |  | a Delaware limited liability company,its sole member
|    |  |                                                      | 
|    |  |                                                      |  | By:                                                  |  | KBS LIMITED PARTNERSHIP II,                   
|    |  |                                                      |  |                                                      |  | a Delaware limited partnership,its sole member
|    |  |                                                      |  |                                                     
|    |  |                                                      |  |                                                      |  | By:                                            |  | KBS REAL ESTATE INVESTMENT TRUST II, INC.,
|    |  |                                                      |  |                                                      |  |                                                |  | a Maryland corporation,general partner    
|    |  |                                                      |  |                                                      | 
|    |  |                                                      |  |                                                      |  |                                                |  | By:                                        |  | /s/ Charles J. Schreiber, Jr.                   
|    |  |                                                      |  |                                                      |  |                                                |  |                                            |  | Charles J. Schreiber, Jr.Chief Executive Officer

Administrative Agent

WELLS FARGO BANK, NATIONAL ASSOCIATION,

as Administrative Agent

By:    /s/ Bryan Stevens

Name: Bryan Stevens

Its: Senior Vice President



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