Presumption about Deference and Extent

 "The circuit court nonetheless deferred to the Technical Review Board's reasoning, correctly noting that courts give "great deference" to an agency's interpretation of its own regulations.
 Holtzman Oil Corp. v. Commonwealth, 32 Va. App. 532, 539, 529 S.E.2d 333, 337 (2000). 
This deference stems from Code § 2.2-4027, which requires that reviewing courts "take due account" of the "experience and specialized competence of the agency" promulgating the regulation.
[ Va. Real Estate Bd. v. Clay, 9 Va. App. 152, 160-61, 384 S.E.2d 622, 627 (1989) (interpreting former Code § 9-6.14:17).]
Even so, "deference is not abdication, and it requires us to accept only those agency interpretations that are reasonable in light of the principles of construction courts normally employ." 
EEOC v. Arabian American Oil Co., 499 U.S. 244, 260 (1991) (Scalia, J., concurring).
 No matter how one calibrates judicial deference, the administrative power to interpret a regulation does not include the power to rewrite it. When a regulation is "not ambiguous," judicial deference "to the agency's position would be to permit the agency, under the guise of interpreting a regulation, to create de facto a new regulation."
[It may be noted that this is also like the prevailing practice in other countries where only the courts interpret the statute unlike the US legal system. In those circumstances the judiciary is generally reluctant to add/subtract words, read in , read down etc, words in /from the statute]
 Christensen v. Harris County, 529 U.S. 576, 588 (2000). 
Though agencies may be tempted to adjudicate their way around unwanted regulations, such overreaching undermines the notice and public hearing procedures of the rulemaking process " thereby putting in jeopardy the "enhanced political accountability of agency policy decisions adopted through the rulemaking process" and the democratic virtue of allowing "all potentially affected members of the public an opportunity to participate in the process of determining the rules that affect them." 
[1 Richard J. Pierce, Jr., Administrative Law Treatise § 6.8, at 369, 372 (4th ed. 2002); see generally 1 Charles H. Koch, Jr., Administrative Law & Practice § 2.12, at 53 (2d ed. 1997)." ]
Board of Supervisors of Culpeper County v. State Building Code Technical Review Board, __ Va. App. __ S.E.2d __ (2008).