Exhibit 5

LUSE GORMAN POMERENK & SCHICK

A PROFESSIONAL CORPORATION

ATTORNEYS AT LAW

5335 Wisconsin Avenue, NW, Suite 780

Washington, D.C. 20015

Telephone (202) 274-2000

Facsimile (202) 362-2902

www.luselaw.com

WRITER’S DIRECT DIAL NUMBER

(202) 274-2000

December 20, 2013

The Board of Directors

New Investors Bancorp, Inc.

101 JFK Parkway

Short Hills, New Jersey 07078

Re: New Investors Bancorp, Inc.

Common Stock, Par Value $0.01 Per Share

Ladies and Gentlemen:

You have requested the opinion of this firm as to certain matters in connection with the offer and sale of the shares of common stock, par value $0.01 per share (“Common Stock”) of New Investors Bancorp, Inc. (the “Company”). We have reviewed the Company’s Certificate of Incorporation, Registration Statement on Form S-1 (the “Form S-1”), as well as applicable statutes and regulations governing the Company and the offer and sale of the Common Stock. The opinion expressed below is limited to matters governed by Delaware and Federal law.

We are of the opinion that upon the declaration of effectiveness of the Form S-1, the Common Stock, when sold, will be legally issued, fully paid and non-assessable.

We hereby consent to our firm being referenced under the caption “Legal Matters” and to the filing of this opinion as an exhibit to the Form S-1.

Very truly yours,

/s/ Luse Gorman Pomerenk & Schick

LUSE GORMAN POMERENK & SCHICK

A PROFESSIONAL CORPORATION