SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

Current Report

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): July 10, 2013

Integrated Electrical Services, Inc.

(Exact name of registrant as specified in Charter)

5433 Westheimer Road, Suite 500, Houston, Texas 77056

(Address of Principal Executive Offices)

Registrant’s telephone number, including area code: (713) 860-1500

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On July 10, 2013, Integrated Electrical Services, Inc., a Delaware corporation (“IES” or the “Company”), MISCOR Group, Ltd., an Indiana corporation (“MISCOR”), and IES Subsidiary Holdings, Inc., a Delaware corporation and a wholly-owned subsidiary of the Company (“Merger Sub”), entered into the First Amendment (the “Amendment”) to that certain Agreement and Plan of Merger, dated March 13, 2013 (the “Merger Agreement”), pursuant to which MISCOR will be merged with and into Merger Sub, with Merger Sub surviving as a wholly-owned subsidiary of the Company (the “Merger”).

Pursuant to the Amendment, (i) the Termination Date has been extended to October 31, 2013 and (ii) the default election provision has been amended to provide that any MISCOR shareholder who does not make a valid election with respect to all or any portion of his or her shares of MISCOR common stock will be deemed to have elected to receive Stock Consideration for such shares for which a valid election has not been made only in the event that the Parent Common Stock Value (as defined in the Merger Agreement) is equal to or greater than $4.024. In the event that the Parent Common Stock Value is less than $4.024, MISCOR shareholders will be deemed to have elected to receive Cash Consideration for such shares for which a valid election has not been made. All other terms of the Merger Agreement remain unchanged.

The foregoing description of the Amendment does not purport to be complete and is qualified in its entirety by reference to the Amendment, which is filed as Exhibit 2.1 hereto and is incorporated by reference into this Item 1.01, and the Merger Agreement, which is filed as Exhibit 2.1 to Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission (the “SEC”) on March 13, 2013.

Important Information for Investors and Security Holders

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. In connection with the proposed Merger, the Company has filed with the SEC a Registration Statement on Form S-4 that includes a joint proxy statement of the Company and MISCOR that also constitutes a prospectus of the Company regarding the proposed transaction. INVESTORS AND SECURITY HOLDERS OF THE COMPANY AND MISCOR ARE URGED TO CAREFULLY READ THE JOINT PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS THAT MAY BE FILED WITH THE SEC WHEN THEY BECOME AVAILABLE BECAUSE THEY CONTAIN IMPORTANT INFORMATION REGARDING THE COMPANY, MISCOR AND THE PROPOSED TRANSACTION. A definitive joint proxy statement/prospectus will be sent to security holders of the Company and MISCOR seeking their approval of the proposed transaction. Investors and security holders may obtain a free copy of the proxy statement/prospectus (when available) and other documents filed by the Company and MISCOR with the SEC at the SEC’s web site at www.sec.gov. You may also read and copy any reports, statements or other information filed with the SEC at the SEC public reference room at 100 F Street N.E., Room 1580, Washington, D.C. 20549. Please call the SEC at (800) 732-0330 or visit the SEC’s website for additional information on its public reference room.

The joint proxy statement/prospectus and such other documents (relating to the Company) may also be obtained from the Company for free (when available) from the Company’s web site at www.ies-corporate.com or by directing a request to: Integrated Electrical Services, Inc., 5433 Westheimer Road, Suite 500, Houston, Texas 77056, Attention: Investor Relations, or by phone at (713) 860-1500. The joint proxy statement/prospectus and such other documents (relating to MISCOR) may also be obtained from MISCOR for free (when available) from MISCOR’s web site at www.miscor.com or by directing a request to: MISCOR Group, Ltd., 800 Nave Rd., SE, Massillon, Ohio 44646, Attention: Investor Relations, or by phone at (330) 830-3500. Information on these websites or any other website is not incorporated by reference herein.

Participants in the Solicitation

IES, its directors, executive officers and certain members of management and employees may be considered “participants in the solicitation” of proxies from IES’ stockholders in connection with the proposed transaction. Information regarding such persons and a description of their interests in the proposed transaction is contained in the joint proxy statement/prospectus filed with the SEC.

MISCOR, its directors, executive officers and certain members of management and employees may be considered “participants in the solicitation” of proxies from MISCOR’s stockholders in connection with the proposed transaction. Information regarding such persons and a description of their interests in the proposed transaction is contained in the joint proxy statement/prospectus filed with the SEC.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX