The information included in this Current
Report on Form 8-K is a supplement to, and is intended to be read together with, the discussion under the heading “Federal
Income Tax Considerations” in the Current Report on Form 8-K filed by CoreSite Realty Corporation (the “Company”)
with the Securities and Exchange Commission (the “SEC”) on July 30, 2018 (File No. 001-34877), including the information
on Exhibit 99.1 thereto (the “Exhibit”), which updated in its entirety, and replaced, the discussion under the heading
“Federal Income Tax Considerations” in the Registration Statement on Form S-3 (File No. 333-177052) of the Company
filed with the SEC on September 28, 2011, and in the related prospectus dated October 11, 2011, and the discussion under the heading
“Federal Income Tax Considerations” in the Registration Statement on Form S-3 (File No. 333-221023) of the Company
filed with the SEC on October 19, 2017, and in the related prospectus.
The following sentence supersedes the eighth sentence
under the heading “Federal Income Tax Considerations—Taxation of Our Company—General—Ownership of Interests
in Taxable REIT Subsidiaries” in the Exhibit.
For taxable years beginning after December 31, 2017, taxpayers
are subject to a limitation on their ability to deduct net business interest generally equal to 30% (or, with respect to certain
years, 50%) of adjusted taxable income (or, if a taxpayer properly elects with respect to certain years, adjusted taxable income
for the prior year), subject to certain exceptions.
The following two sentences supersede the first two sentences
of the fourth paragraph under the heading “Federal Income Tax Considerations—Taxation of Our Company—Annual Distribution
Requirements” in the Exhibit.
For taxable years beginning after December 31, 2017, and except
as provided below, our deduction for net business interest expense will generally be limited to 30% (or, with respect to certain
years, 50%) of our taxable income (or, if we properly elect with respect to certain years, our taxable income for the prior year),
as adjusted for certain items of income, gain, deduction or loss. Any business interest deduction that is disallowed due to this
limitation may be carried forward to future taxable years, subject to special rules applicable to partnerships.
The following discussion supersedes the discussion in
the Exhibit under the heading “Federal Income Tax Considerations—Material Federal Income Tax Considerations for Holders
of Our Common Stock—Taxation of Non-U.S. Stockholders—Foreign Accounts.”
Foreign Accounts. Withholding
taxes may be imposed under Sections 1471 through 1474 of the Code (commonly referred to as the Foreign Account Tax Compliance
Act, or FATCA) on certain types of payments made to non-U.S. financial institutions and certain other non-U.S. entities.
Specifically, a 30% withholding tax may be imposed on dividends on, or (subject to the proposed Treasury Regulations
discussed below) gross proceeds from the sale or other disposition of, our stock paid to a “foreign financial
institution” or a “non-financial foreign entity” (each as defined in the Code), unless (1) in the case of a
foreign financial institution, the foreign financial institution undertakes certain diligence and reporting obligations, (2)
in the case of a non-financial foreign entity, the non-financial foreign entity either certifies it does not have any
“substantial United States owners” (as defined in the Code) or furnishes identifying information regarding each
substantial United States owner or (3) the foreign financial institution or non-financial foreign entity otherwise qualifies
for an exemption from these rules. If the payee is a foreign financial institution and is subject to the diligence and
reporting requirements referred to in clause (1) above, it must enter into an agreement with the U.S. Department of the
Treasury requiring, among other things, that it undertake to identify accounts held by certain “specified United States
persons” or “United States-owned foreign entities” (each as defined in the Code), annually report certain
information about such accounts and withhold 30% on certain payments to non-compliant foreign financial institutions and
certain other account holders. Non-U.S. persons located in jurisdictions that have an intergovernmental agreement with the
United States governing FATCA may be subject to different rules.
Under the applicable Treasury Regulations
and administrative guidance, withholding under FATCA generally applies to payments of dividends on our common stock. While withholding
under FATCA would have also applied to payments of gross proceeds from the sale or other disposition of our stock, proposed Treasury
Regulations eliminate FATCA withholding on payments of gross proceeds entirely. Taxpayers generally may rely on these proposed
Treasury Regulations until final Treasury Regulations are issued.
Prospective investors should consult their
tax advisors regarding these rules.