(dissenting, with whom Grainger, J., joins). The proper inquiry remains “ ‘whether, on the facts the judge has found, any rational board could conclude’ that the additional” fourteen mobile homes “would be substantially more detrimental to the neighborhood” than the existing sixty-four mobile homes. Cumberland Farms, Inc. v. Zoning Bd. of Appeals of Walpole, 61 Mass. App. Ct. 124, 131 (2004), quoting from Britton v. Zoning Bd. of Appeals of Gloucester, 59 Mass. App. Ct. 68, 74 (2003). I agree with the judge that none of the reasons cited by the board supports the denial of the application.
*25The board contends that the judge erred because the proposed plan does not comply with the setback and frontage requirements for single-family homes in the residential zones at issue. It is true that in Cox v. Board of Appeals of Carver, 42 Mass. App. Ct. 422, 426 (1997), this court reaffirmed that pursuant to G. L. c. 40A, § 6, an extension of a nonconforming use must comply with the zoning ordinance or by-law in addition to the requirement that the extension not be substantially more detrimental to the neighborhood. For example, in Cox, expansion of a mobile home park onto a newly acquired 2.53-acre adjacent lot was prohibited where the zoning by-law at issue required a minimum lot size of 100 acres for the operation of a mobile home park. Here, however, the proposed expansion is on the original lot and there is no suggestion that it is undersized. As for the setback and frontage requirements, so far as the record reflects, the setback and frontage requirements for single-family homes have never been applied to mobile homes in a mobile home park in the town. There is no suggestion in the record that the board of appeals determined that lot area and setback requirements other than those set forth in the board of health regulations apply to each individual mobile home in the park. The town has controlled frontage and setbacks in mobile home parks through the board of health regulations and the proposed expansion complies with those regulations. I discern no error, therefore, in the judge’s refusal to apply the setbacks for single-family homes in the district.
I particularly disagree with the majority’s treatment of the issue of density, on which the board’s purported reliance, in my view, is fatally vague.
I recognize that the proposed expansion will add fourteen units to a mobile home park, the existing developed portion of which is already denser than allowed under the board of health regulations. Pursuant to the local by-law, however, expansion of a nonconforming use is permitted provided it does not exceed twenty-five percent of its area on the lot and there is a finding that the expansion is not substantially more detrimental to the neighborhood than the existing use. The proposed expansion does not exceed the twenty-five percent density limitation and the board has failed to express in any meaningful way how the *26addition of fourteen units will be substantially more detrimental to the neighborhood than the existing sixty-four units in terms of density or in any other regard.
No abutter testified at trial in opposition to the expansion. While the plan shows that the units will be closer than the existing units to three abutters, the judge found that the new mobile homes will be well screened by trees and other buffers. The board’s unexplained reference to density, albeit a concern within the scope of the zoning statutory scheme, fails to bring the decision out of the realm of arbitrary and capricious, particularly where the by-law itself establishes a maximum density for expansion of nonconforming uses.
Finally, I do not agree with the board’s argument that it may deny a permit based on its desire to prevent any additional mobile homes simply because the use has been eliminated from the allowed uses throughout the town. In considering an application for a special permit to expand a nonconforming use, we said in Davis v. Zoning Bd. of Chatham, 52 Mass. App. Ct. 349, 357 (2001), that “reliance on the undesirable enlargement of the existing nonconformity that would result from the plaintiffs’ proposed project would itself be sustainable.”1 There, however, the board had found that the expansion of a pier would result in the loss of boat moorings and would significantly increase the impediment to the harvesting of shellfish. Id. at 353-354. There was evidence, therefore, to support the conclusion that the undesirable enlargement of the nonconformity would be substantially more detrimental to the neighborhood than the existing nonconformity. Here, even if we were to assume that a desire to eliminate uses no longer allowed in the town is a proper criteria to consider in reviewing an application under § 2.8.4, where the evidence demonstrates that there will be no substantial impacts on the value of the neighboring properties, traffic, infrastructure or other zoning concerns, denial is improper in the absence of any evidence to support a finding that the expansion would be substantially more detrimental to the neighborhood than the existing use.
*27In sum, the record reveals that the evidence before the judge does not support the rationale relied on by the board in many respects. That the proposed expansion approaches but does not exceed the twenty-five percent limitation allowed under the bylaw is no reason in and of itself to deny the permit. Moreover, even the majority acknowledges that the board’s concerns about the impact on the school system were disingenuous at worst and speculative at best.
In Davis v. Zoning Bd. of Chatham, 52 Mass. App. Ct. 349 (2001), the panel did not consider whether there was a difference between a special permit for expansion of a nonconforming use and a regular special permit.