Filed by the Registrant x    Filed by a Party other than the Registrant ¨

May 23, 2019

We invite you to attend the 2019 annual meeting of shareholders (the "Annual Meeting") of National Storage Affiliates Trust, a Maryland real estate investment trust (the "Company," "we," "our" or "us").

April 5, 2019

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting to be held on May 23, 2019. The Proxy Statement, our 2018 Annual Report to Shareholders, and the means to vote in person or by Internet, telephone or mail are available at: www.proxyvote.com. You will need to enter the control number found on your proxy card to access these materials via the Internet.

Our trustee nominees represent a mix of independence, age, gender, tenure, skills and experience:

(2) Source: 2019 Self-Storage Almanac, based on number of properties with company ownership.

This Proxy Statement, the Notice of Annual Meeting of Shareholders and the related proxy card are first being made available to shareholders on or about April 5, 2019.

The Annual Meeting will be held at 8400 East Prentice Avenue, 2nd Floor, Greenwood Village, Colorado 80111, on May 23, 2019, at 8:00 a.m., local time, or at any postponements or adjournments thereof.

The record date is March 29, 2019.

Holders of our Common Shares on the close of business on the record date are entitled to vote. For all matters submitted for a vote at the Annual Meeting, each Common Share is entitled to one vote. As of March 29, 2019, we had 56,699,541 Common Shares that are issued, outstanding and entitled to vote at the Annual Meeting (including unvested restricted Common Shares).

A broker non-vote occurs when a nominee holding shares for a beneficial owner (i.e., a brokerage firm, bank, broker-dealer or other intermediary) delivers a properly-executed proxy but does not vote on a particular proposal because the nominee does not have discretionary voting power for that particular matter and has not received instructions from the beneficial owner.

•FOR the election of the nominees named in this Proxy Statement as trustees;

•FOR the ratification of the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2019; and

•FOR the approval of the compensation of the Named Executive Officers as described in this Proxy Statement.

If your hold your Common Shares in "street name" through a brokerage firm, bank, broker-dealer or other intermediary, then under NYSE rules, your nominee may vote your Common Shares without receiving instructions from you only with respect to the ratification of the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2019. All other matters that are to be voted upon at the Annual Meeting are considered to be "non-routine" matters. If you hold your shares in street name and do not give the intermediary specific voting instructions on the election of trustees or the advisory vote regarding the compensation of our Named Executive Officers, your shares will not be voted on those items, and a broker non-vote will occur. Broker non-votes and abstentions will have no effect on the voting results for any of the proposals.

•By Internet: To use the Internet to transmit your voting instructions and for electronic delivery of information, have your proxy card in hand when you access the website at www.proxyvote.com, and follow the instructions to obtain your records and to create an electronic voting instruction form. If you hold your shares in street name, you should follow the instructions provided by your brokerage firm, bank, broker-dealer or other intermediary. Voting instructions transmitted by Internet must be received by 11:59 P.M. Eastern Time on May 22, 2019.

•By Phone: To transmit your voting instructions by telephone, use any touch-tone telephone to dial 1-800-690-6903. Have your proxy card in hand when you call and then follow the instructions. If you hold your shares in street name, you should follow the instructions provided by your brokerage firm, bank, broker-dealer or other intermediary. Voting instructions transmitted by telephone must be received by 11:59 P.M. Eastern Time on May 22, 2019.

•By Mail: To transmit your voting instructions by mail, mark, sign and date your proxy card and return it in the postage-paid envelope we have provided or return it to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, New York 11717. If you hold your shares in street name, you should follow the instructions provided by your brokerage firm, bank, broker-dealer or other intermediary. Your proxy card must be received by May 22, 2019.

•In Person at the Annual Meeting: If you are registered holder of Common Shares and attend the meeting, you may vote in person at the Annual Meeting. If you hold your Common Shares in street name, you must obtain a proxy form from your brokerage firm, bank, broker-dealer or other intermediary in order to vote your Common Shares at the Annual Meeting. To vote in person at the Annual Meeting, you will be required to present a valid form of identification.

This Proxy Statement is accompanied by our annual report on Form 10-K, as supplemented by our Form 10-K/A, for the year ended December 31, 2018 (collectively, our "Form 10-K"), which is our Annual Report to Shareholders for the year ended December 31, 2018.

Our board of trustees is currently comprised of nine trustees. Kevin M. Howard, one of our current trustees, has elected to retire from the Board effective May 23, 2019, the date of our Annual Meeting. Accordingly, Mr. Howard is not standing for re-election at the Annual Meeting.  Upon the recommendation of our CNCG Committee, our board of trustees has determined to maintain the size of our board at nine trustees, has nominated our other current trustees for re-election, and has also nominated J. Timothy Warren to stand for election at the Annual Meeting. As a result, the trustee nominees standing for re-election or election, as the case may be, at the Annual Meeting are listed below.

We seek highly qualified trustee candidates from diverse business, professional and educational backgrounds who combine a broad spectrum of experience and expertise with a reputation for the highest personal and professional ethics, integrity and values. The CNCG Committee considers diversity of gender, age, experience and skills as important factors in choosing the most qualified candidates. We believe that, as a group, the nominees bring a broad range of perspectives that contribute to the effectiveness of our board of trustees as a whole. The procedures and considerations of the CNCG Committee in recommending qualified trustee candidates are described below under "Corporate Governance–Identification of Trustee Candidates" in this Proxy Statement. The CNCG Committee and our board of trustees concluded that each of our trustee nominees should be nominated for election based on the qualifications and experience described in the biographical information below under "–Information Regarding Nominees for Election as Trustees."

It is intended that the Common Shares represented by properly submitted proxies will be voted by the persons named therein as proxy holders FOR the election of Messrs. Nordhagen, Chapman, Hylbert, Meisinger, Osgood, Palazzo, Van Mourick and Warren and Ms. Steinfort as trustees, unless otherwise instructed. If the candidacy of any trustee nominee should, for any reason, be withdrawn prior to the Annual Meeting, the proxies will be voted by the proxy holders in favor of such substituted candidates (if any) as shall be nominated by our board of trustees. Our board of trustees has no reason to believe that, if elected, any of the nominees will be unable or unwilling to serve as a trustee.

We have not received notice of any additional candidates to be nominated for election as trustees at the Annual Meeting and the deadline for notice of additional candidates has passed. Consequently, the election of trustees will be an uncontested election and the provisions of our Second Amended and Restated Bylaws (the "Bylaws") providing for majority voting in uncontested elections will apply. See "Corporate Governance–Majority Vote and Trustee Resignation Policy" below. Under majority voting, to be elected as a trustee, a nominee must receive votes "FOR" his or her election constituting a majority of the total votes cast for and against such nominee at the Annual Meeting at which a quorum is present. If a nominee who currently is serving as a trustee does not receive sufficient "FOR" votes to be re-elected, Maryland law provides that the trustee would continue to serve on our board of trustees as a "holdover" trustee. Under our Bylaws and corporate governance guidelines (the "Guidelines"), he or she must submit his or her resignation to our board of trustees. Our CNCG Committee will consider such tendered resignation and recommend to our board of trustees whether to accept it. Our board of trustees will decide whether to accept any such resignation within 90 days after certification of the election results and will publicly disclose its decision. If the resignation is not accepted, the trustee will continue to serve until the trustee's successor is duly elected and qualifies or until the trustee's earlier death, resignation, retirement or removal. If a trustee’s offer to resign is accepted by our board of trustees, or if a nominee for trustee is not elected and the nominee is not an incumbent trustee, then our board of trustees, in its sole discretion, may fill any resulting vacancy pursuant to the Bylaws. Proxies solicited by our board of trustees will be voted FOR Messrs. Nordhagen, Chapman, Hylbert, Meisinger, Osgood, Palazzo, Van Mourick and Warren and Ms. Steinfort, unless otherwise instructed. Abstentions and broker non-votes will not be counted as votes cast and will have no effect on the result of the vote, although they will be considered present for the purpose of determining the presence of a quorum.

The audit committee of our board of trustees (the "Audit Committee") has appointed KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2019. Our board of trustees is requesting that our shareholders ratify this appointment of KPMG LLP.

The following table summarizes the aggregate fees billed to us for professional services provided by KPMG LLP for the years ended December 31, 2018 and 2017.

Our board of trustees recommends a vote FOR the ratification of the appointment of KPMG LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2019.

"RESOLVED, that our shareholders approve, on an advisory basis, the compensation of our Named Executive Officers as described in this Proxy Statement for the 2019 Annual Meeting of Shareholders pursuant to the compensation disclosure rules of the SEC, including the Compensation Discussion and Analysis, the Summary Compensation Table and the other related tables and narrative disclosure."

Our board of trustees is responsible for overseeing our affairs. Our board of trustees conducts its business through meetings and actions taken by written consent in lieu of meetings. Our board of trustees intends to hold at least four regularly scheduled meetings per year and additional special meetings as necessary. During 2018, our board of trustees held eight meetings. All of our trustees attended at least 75% of the meetings of our board of trustees and of the Audit Committee, CNCG Committee and Investment Committee on which they served during this period, either in person or telephonically. Our board of trustees' policy, as set forth in our Guidelines, is to encourage and promote the attendance by each trustee at all scheduled meetings of our board of trustees and all meetings of our shareholders.

The Audit Committee has furnished the following report for the fiscal year ending December 31, 2018:

The Audit Committee held seven meetings in 2018. Representatives of KPMG LLP were in attendance at six of our Audit Committee meetings. These meetings were designed, among other things, to facilitate and encourage communication among the Audit Committee, management and KPMG LLP. At these meetings, among other things, the Audit Committee reviewed and discussed with management the consolidated financial statements contained in our quarterly and annual periodic reports, as applicable, as well as our earnings releases. The Audit Committee also discussed with KPMG LLP matters that independent accounting firms must discuss with audit committees under generally accepted auditing standards and standards of the Public Company Accounting Oversight Board ("PCAOB"), including, among other things, matters related to the conduct of the audit of our consolidated financial statements and the matters

Based on the Audit Committee's review and these meetings, discussions and reports, and subject to the limitations on the Audit Committee's role and responsibilities referred to above and in its written charter, the Audit Committee unanimously recommended to our board of trustees that our audited consolidated financial statements for the fiscal year ended December 31, 2018 be included in our annual report on Form 10-K filed with the SEC.

For 2018, each of our independent trustees was eligible to receive annual compensation as follows:

The table below summarizes the annual compensation received by our independent trustees during 2018.

Each independent trustee is subject to our minimum equity ownership guidelines. See "Compensation Discussion and Analysis–Minimum Equity Ownership Guidelines."

Our board of trustees has adopted Corporate Governance Guidelines that address significant issues of corporate governance and set forth procedures by which our board of trustees carries out its responsibilities, including the trustee resignation policy as described under "–Majority Vote and Trustee Resignation Policy" below. In addition, among the areas addressed by the Guidelines are the composition of our board of trustees, its functions and responsibilities, its standing committees, its PRO advisory committee, trustee qualification standards, access to management and independent advisors, trustee compensation, management succession, trustee orientation and continuing education, and the annual performance evaluation and review of our board of trustees and committees. The Guidelines are available for viewing on our website at www.nationalstorageaffiliates.com. We will also provide the Guidelines, free of charge, to shareholders who request it. Requests should be directed to Tamara D. Fischer, our president, chief financial officer, treasurer and secretary, at National Storage Affiliates Trust, 8400 East Prentice Avenue, 9th Floor, Greenwood Village, CO 80111.

Our board of trustees has approved a process to enable communications with the independent members of the board of trustees, including our lead independent trustee, or the chair of any of the committees of the board of trustees. Communications by email should be sent to NSABoard@nsareit.net. Communications by regular mail should be sent to the attention of Tamara D. Fischer, our president, chief financial officer, treasurer and secretary, at National Storage Affiliates Trust, 8400 East Prentice Avenue, 9th Floor, Greenwood Village, CO 80111. Each communication received will be reviewed to determine whether the communication requires immediate action. All appropriate communications received, or a summary of such communications, will be sent to the appropriate member(s) of our board of trustees. However, we reserve the right to disregard any communication we determine is unduly hostile, threatening, illegal, does not reasonably relate to us or our business, or is similarly inappropriate. Our secretary, or her delegate, has the authority to disregard any inappropriate communications or to take other appropriate actions with respect to any such inappropriate communications. In addition, any of our shareholders and any other person may make a good faith report to the Audit Committee regarding any questionable or unethical accounting or auditing matters via regular mail addressed to the Audit Committee, National Storage Affiliates Trust, 8400 East Prentice Avenue, 9th Floor, Greenwood Village, CO 80111. We also encourage members of our board of trustees to be available to speak to institutional shareholders outside of formal meeting settings.

Our board of trustees values the input and insights of our shareholders and believes that effective shareholder engagement strengthens the board's role as an informed and engaged fiduciary. We are committed to serving our shareholders’ interests, and recognize that communicating with shareholders on a regular basis is a critical component of our corporate governance program. As part of this commitment, management actively engages with our shareholders in order to fully understand their viewpoints concerning our company, to gather feedback on what we can do better and to help our shareholders understand our performance and strategy. In addition to answering questions from shareholders on our quarterly earnings calls, our management regularly engages with shareholders by participating in industry conferences, through in-person meetings with our shareholders and prospective investors, and by telephone with many shareholders at other times throughout the year to solicit input and answer questions on a variety of topics. During 2018, we held approximately 190 such meetings with current and prospective investors to discuss various key corporate matters, including our differentiated growth strategy, financing strategy, risk management practices, and strong corporate governance practices. Interested parties, including shareholders, may communicate their concerns directly to the independent members of our board of trustees, including our lead independent trustee, or the chair of any of the committees of the board of trustees as described above under "–Communications with the Board of Trustees," or to management.

▪nominated our first female trustee, who was elected at our 2018 Annual Meeting;

▪implemented majority voting in uncontested elections together with a trustee resignation policy (see "–Majority Vote and Trustee Resignation Policy" below); and

▪provided equityholders with the right to amend our Bylaws (see "–Bylaw Amendments" below).

•holders of a majority of the Company's Common Shares outstanding as of the Determination Date (as defined below); and

•holders of Common Shares and limited partners (other than the Company) of our operating partnership representing a majority of the number of Common Shares outstanding as of the Determination Date together with the number of additional Common Shares that would be issuable if:

–all Class A common units of limited partner interest in our operating partnership ("OP units") outstanding as of the Determination Date were exchanged on a one-for-one basis, subject to adjustments as provided in the Third Amended and Restated Agreement of Limited Partnership of our operating partnership (as amended, the "Partnership Agreement"), for Common Shares, and

–the OP units which would be outstanding if each series of Class B common units of limited partner interest in our operating partnership ("subordinated performance units") (or other similar class or series of OP units created from time to time) outstanding as of the Determination Date (whether or not then convertible) were converted into OP units using the conversion ratio for each such class or series in effect as of the last day of the most recent fiscal year determined pursuant to the terms of the Partnership Agreement and as approved by the Company's board of trustees, were exchanged on a one-for-one basis, subject to adjustments as provided in the Partnership Agreement, for Common Shares.

Biographies for our executive officers as of December 31, 2018, other than Mr. Nordhagen, are set forth below. Biographical information for Mr. Nordhagen is set forth under "Proposal 1: Election of Trustees–Information Regarding the Nominees for Election as Trustees." All of our executive officers are Named Executive Officers. As referenced below, effective July 1, 2018:

•Ms. Fischer became our president, chief financial officer, treasurer and secretary;

•Mr. Treadwell became our executive vice president, chief operating officer and president of National Storage Affiliates Trust Management Company;

•Mr. Togashi became our senior vice president, chief accounting officer and controller; and

•Mr. Nordhagen's title reflects the appointment of Ms. Fischer as president, and Mr. Nordhagen continues to serve as our chairman and chief executive officer.

We are focused on the ownership, operation, and acquisition of self storage properties located within the top 100 metropolitan statistical areas ("MSAs") throughout the United States. As of December 31, 2018, we held ownership interests in and operated a geographically diversified portfolio of 675 self storage properties, located in 34 states and Puerto Rico, comprising approximately 43.0 million rentable square feet, configured in approximately 345,000 storage units. According to the 2019 Self-Storage Almanac, we are the fifth largest owner and operator of self storage properties in the United States, based on number of properties with company ownership.

Our 2018 financial highlights include the following:

The above chart assumes $100.00 invested on April 23, 2015, with dividends reinvested and compares the yearly cumulative total shareholder return ("TSR") for our common shares with the cumulative shareholder return of companies on (i) the S&P 500 Index, (ii) the Russell 2000 Index, (iii) the Nareit All Equity REIT Index as provided by Nareit, and (iv) the Morgan Stanley Capital International US REIT Index (the "MSCI US REIT Index"), for the period beginning April 23, 2015 and ending December 31, 2018. We have included the MSCI US REIT Index as we utilize that index as a metric for our long-term equity incentive program.

Based on our average annual TSR performance of 20.62% over the three-year period ended December 31, 2018, we outperformed our public company self storage REIT peers and ranked 9th out of 141 REITs in the MSCI US REIT Index.

Source: Bloomberg

We also completed a significant number of acquisitions in 2018.

CNCG Committee

Compensation Consultant

The market data for our Named Executive Officers was sourced from FPL’s proprietary database and the 2016, 2017 and 2018 Nareit Compensation Surveys conducted by FPL. For our independent trustees, the market data was sourced from the January 2017 National Association of Corporate Directors Director Compensation Report, an August 31, 2017 SNL Financial Report and the public filings of the REITs included in the analysis. This information was considered by our CNCG Committee in approving increased annual base salaries to our Named Executive Officers in 2018 and 2019, as set forth below under "Elements of our Compensation–Base Salary." The independent trustee Benchmarking Analysis was considered by our CNCG Committee in approving our independent trustee compensation program for 2018, as described above under "Compensation of Independent Trustees." These changes are intended to better align each Named Executive Officer's and independent trustee's total compensation with the peer group.

We strive to adopt policies and practices that we believe are in the best interests of our Company and our shareholders. See "Corporate Governance–Governance Highlights" and "Corporate Governance–Active Shareholder Outreach and Corporate Governance" for additional information.

KEY FEATURES OF OUR COMPENSATION PROGRAM

Base Salary

Base salaries are a fixed component of compensation that reflects each Named Executive Officer's position and responsibilities. Base salaries are reviewed annually by our CNCG Committee and may be adjusted to better match competitive market levels or to recognize a Named Executive Officer's professional growth, development, and increased responsibility. The table below summarizes the 2018 and 2017 base salary and corresponding percentage change against the prior year for each Named Executive Officer:

For 2019, our CNCG Committee revised the base salaries for our Named Executive Officers in line with our compensation objectives. Our CNCG Committee approved base salary levels for 2019 for Mr. Nordhagen, Ms. Fischer, Mr. Treadwell and Mr. Togashi of $500,000, $370,000, $335,000 and $250,000, respectively. Such revised base salaries are intended to preserve an appropriate mix of compensation such that base salary remains a modest portion of the overall compensation opportunity for each Named Executive Officer.

Annual Incentive Cash Bonus Payments

Long-Term Equity Incentive Compensation

•Encourage management to create shareholder value over the long-term;

•Promote management retention because full vesting of the awards generally requires continued employment for multiple years; and

•Encourage company growth and the achievement of our business strategies that can take more than one year to execute when they are tied to specific performance criteria.

Restricted Shares

Dividend Equivalents

LTIP Units

Other Equity-Based Awards

AMENDMENTS AND TERMINATION