The defendants, Robert Jeffrey Chandler and Jayne Kerry Chandler (collectively the Chandlers), appeal from the entry of summary judgment by a judge of the Land Court that reversed a decision of the zoning board of appeals of Chatham (board). The board had granted the Chandlers a special permit allowing them to reconstruct a pre-existing nonconforming structure on their nonconforming lot. In reversing the board’s decision, the judge determined that because the proposed new structure’s increased height created a new, additional nonconformity, distinct from the pre-existing dimensional and coverage nonconformities, a variance was required. We agree with the judge’s decision that a variance would be required if the proposed increase in height constitutes an additional nonconformity not otherwise exempted by the town by-law. However, we also conclude that the judge erroneously concluded that the board had determined that the Chandlers’ project is ineligible for the exemption from certain height limits created by § IV.A.3 of the Chatham bylaw.4 Consequently, we vacate the entry of summary judgment and remand the matter for further proceedings before the board.

1. Facts. The following undisputed facts are taken from the summary judgment record. On July 1, 2005, the Chandlers purchased property, located at 24 Windmill Lane in Chatham, containing a single-family home (old structure). The old structure was built in approximately 1929 and is located within a residential R-40 district and in a coastal conservancy district.5 The old structure is 19.2 feet high above grade, and contains 2,161 square feet of living space. The Chandlers’ property is nonconforming as to lot size and building coverage, and contains *541additional dimensional nonconformities with respect to its frontage, front yard setback, and side yard setback.

In November, 2007, the Chandlers filed an application for a special permit seeking to raze the old structure and replace it with a new structure. The new structure, as proposed, will contain an additional 529 square feet of living space on substantially the same footprint as the old structure.6 The new structure maintains the same nonconformities as the old structure with respect to frontage, setbacks, lot size, and building coverage. However, the height of the new structure is 27.2 feet above grade and, therefore, exceeds the maximum allowable height of twenty feet in the coastal conservancy district.

Part of this height increase is due to the property’s location in a “velocity zone” as designated by the Federal Emergency Management Agency (FEMA), which mandates pilings instead of a foundation. Pursuant to FEMA regulations, any “substantial improvement” to a structure located within a velocity zone must be built on pilings with an elevation above the 100-year flood elevation.7 The proposed height of the new structure, not including the FEMA foundation, is 23.5 feet above flood elevation.8

2. Procedural history. On December 31, 2007, John V.C. Saylor, Georgia A. Saylor, Peter Hallock, Edwin J. Deadrick, and Mary Anne Hall Deadrick filed their complaint appealing from the board’s decision to grant a special permit to the Chandlers, pursuant to G. L. c. 40A, § 17.9 The plaintiffs filed *542a second amended complaint10 on March 5, 2008, which added a count under G. L. c. 240, § 14A, seeking an interpretation of § V.B and § IV.A.3 of the Chatham zoning bylaws.

Thereafter, both parties filed cross motions for summary judgment. A judge of the Land Court allowed the Chandlers’ motion, concluding that the plaintiffs lacked standing to challenge the special permit. However, in Hallock v. Zoning Bd. of Appeals of Chatham, 80 Mass. App. Ct. 1104 (2011), an unpublished decision pursuant to rule 1:28 (2011 decision), a panel of this court determined that the Deadricks had standing, and remanded the case to the Land Court.11

On remand, both parties renewed their cross motions for summary judgment. In a decision dated February 21, 2013, the Land Court judge allowed the plaintiffs’ motion for summary judgment and reversed the board’s decision granting the special permit. The judge reasoned that, since the new structure created an additional nonconformity as to its height, the project required a variance rather than a special permit.

On March 6, 2013, the Chandlers filed a motion for reconsideration, or in the alternative, for a ruling on their pending motion for entry of final judgment, arguing that the 2011 decision of this court had determined the merits of the case favorably to them. On April 9, 2013, the Chandlers also filed a motion under Mass.R.Civ.P. 60(b), 365 Mass. 828 (1974), seeking relief from the judgment on the basis that the last surviving original plaintiff, Mary Anne Deadrick, had died in July, 2012, resulting in a “gap in the title.” Thus, the Chandlers claimed that the judgment should be vacated and the complaint dismissed for lack of an aggrieved party at the time the judgment entered. In response, Mary Anne Hall Deadrick’s daughter, Sara Dead-rick Frye (Frye), acting in her capacity as executor of her mother’s estate, filed a motion under Mass.R.Civ.P. 17(a), as amended, 454 Mass. 1401 (1982), to be substituted as plaintiff *543for her deceased mother. On the same day, Sara Deadrick Frye and Mary Anne Hall Deadrick’s other children, Stuart Hall Deadrick and Spencer Hall Deadrick (collectively the Deadrick children), appearing in their individual capacities, filed a motion under Mass.R.Civ.P. 20(a), 365 Mass. 766 (1974), seeking to be joined as plaintiffs in this action.12 The motions for substitution and joinder were allowed on April 30, 2013, but the Land Court judge took under advisement the Chandlers’ rule 60(b) motion on the issue of the Deadrick children’s standing.

In an order dated June 4, 2013, the judge determined that, because the Deadrick children had some ownership interest in the property from the outset of the dispute, they shared the same harm as their parents. Therefore, the judge concluded the Deadrick children had standing because this court previously had determined that their parents’ harm was a basis for standing. In the same order, the judge denied the Chandlers’ motion for reconsideration, noting that the 2011 decision was limited to the issue of standing. The judge also rejected the Chandlers’ additional argument that § IV.A.3 of the Chatham bylaw, discussed infra, permitted the Chandlers to exceed the applicable maximum height restriction. The judge concluded that the board had determined that the new structure constituted an “expansion” under § IV.A.3 of the bylaw, and therefore was ineligible for its exemption from applicable height restrictions; he also expressed his view that if the board had determined that it was not an expansion, such a decision would be arbitrary and capricious. In any event, the judge ruled that the height exemption provided by § IV.A.3 was inapplicable, so that the new structure’s increased height created a new nonconformity requiring a variance.

3. Discussion. “We review the Land Court judge’s summary *544judgment decision de nova. Because the judge does not engage in fact finding in ruling on cross motions for summary judgment, we owe no deference to his assessment of the record.” Marhefka v. Zoning Bd. of Appeals of Sutton, 79 Mass. App. Ct. 515, 517 (2011) (footnote and citations omitted). Turning to the merits of the Chandlers’ appeal,13 we first consider whether the judge correctly decided two issues: (1) whether the board considered the applicability of § IV.A.3 of the bylaw to the new structure, while weighing the Chandler’s application for a special permit, and (2) whether the addition of new nonconformities to a pre-existing nonconforming residential structure require a variance or special permit.

On remand after the 2011 decision, the judge properly recognized that the decision was limited to the issue of standing. Specifically, the judge correctly understood that he needed to determine if the board had ruled on the applicability of § IV.A.3 of Chatham’s zoning bylaw to the new structure; as he stated: “The first issue is whether the ZBA made a finding as to whether or not the New structure was an expansion of the Old structure.”

Section IV.A.3 of the bylaw exempts certain structures from otherwise applicable height restrictions if FEMA regulations require the additional height. See note 5, supra. Accordingly, if the new structure is not an “expansion” within the meaning of § IV.A.3, then it qualifies for the exemption created by that section from the otherwise applicable twenty-foot height restriction. The increased height would not be a new nonconformity, and the Chandlers may proceed under their special permit. However, in denying the Chandlers’ motion for reconsideration, the judge concluded that the zoning board had already found *545the new structure to be an “expansion,” within the meaning of § IV.A.3 and, therefore, confirmed his conclusion that the Chandlers’ project required a variance rather than a special permit.

The question of the applicability of § IV.A.3 to the new structure is significant. As discussed below, we conclude that the Land Court judge correctly ruled that the creation of a new nonconformity in a preexisting nonconforming structure requires a variance, and not just a special permit based on substantial detriment pursuant to the second sentence of G. L. c. 40A, § 6. Accordingly, if the new structure is ineligible for the exemption created by § IV.A.3, it requires a variance and the board’s decision granting a special permit for the project would be invalid. Conversely, if the new structure is eligible for the exemption created by § IV.A.3, it does not require a variance and the project may proceed by special permit.

a. Applicability of § IV.A.3 to the new structure. As we have observed, the Land Court judge correctly recognized that his first task following the remand ordered by the 2011 decision was to determine whether the board considered and determined the applicability of § IV.A.3 to the new structure in its special permit decision. “[Ajlthough interpretation of the by-law is in the last analysis a judicial function, deference is owed to a local zoning board’s home grown knowledge about the history and purpose of its town’s zoning by-law.” Duteau v. Zoning Bd. of Appeals of Webster, 47 Mass. App. Ct. 664,669 (1999). “Reviewing courts will interpret zoning by-laws ‘in accordance with ordinary principles of statutory construction, with some measure of deference given to the board’s interpretation.’ ” Eastern Point, LLC v. Zoning Bd. of Appeals of Gloucester, 74 Mass. App. Ct. 481, 486 (2009), quoting from APT Asset Mgmt., Inc. v. Board of Appeals of Melrose, 50 Mass. App. Ct. 133, 138 (2000). Accordingly, the interpretation of the application of a provision of a local zoning by-law to a request for a special permit ordinarily should be undertaken in the first instance by the local board acting as the special permit granting authority, and only thereafter subject to judicial review within the context of an appeal pursuant to G. L. c. 40A, § 17.

We disagree, however, with the Land Court judge’s conclu*546sion that the board considered and determined the applicability of § IV.A.3 to the new structure in its special permit decision. The board’s decision does not expressly refer to § IV.A.3. Nor does it appear that the board’s use of the term “expand” within its decision was intended to express a conclusion that the new structure constitutes an “expansion” within the meaning of § IV.A.3, making the new structure ineligible for the height exemption it provides.14 Instead, when the board’s decision is considered as a whole, we conclude that its use of the word “expand,” in two places, was merely descriptive, in a general sense, of the new structure proposed by the Chandlers’ application for a special permit. The board’s only mention of height was in the board’s finding that the height was “not out of scale for the neighborhood.” Significantly, even this single finding was within the board’s analysis of whether the new structure was substantially more detrimental to the neighborhood. In fact, the board’s decision appears to focus principally, if not exclusively, on whether the new structure would be “substantially more detrimental to the neighborhood,” under the rubric of G. L. c. 40A, § 6. We conclude that the board did not consider or determine the applicability of § IV.A.3 to the new structure in its special permit decision.

As we have observed, zoning is a local matter, and questions of interpretation of the local zoning bylaw ordinarily are matters for the local board charged with administration of the bylaw, with some deference thereafter due to the board’s resulting interpretation. Here, however, there was no initial determination by the board as to the applicability of § IV.A.3 to the Chandlers’ new structure.

Moreover, whether the new structure is an expansion under § IV.A.3 is at least a mixed question of law and fact. As such, the proper application of § IV.A.3 to the particularities of the new structure depends to a great extent on what the municipality intended to achieve by enactment of that section. Since “[t]he object of all statutory construction is to ascertain the true *547intent of the Legislature from the words used. If a liberal, even if not literally exact, interpretation of certain words is necessary to accomplish the purpose indicated by the words as a whole, such interpretation is to be adopted rather than one which will defeat that purpose.” Dennis Hous. Corp. v. Zoning Bd. of Appeals of Dennis, 439 Mass. 71, 83 (2003), quoting from Champigny v. Commonwealth, 422 Mass. 249, 251 (1996). Given the board’s local, particularized “home grown” knowledge, we conclude that the board is entitled here to interpret its own bylaw in the first instance.15 See Duteau v. Zoning Bd. of Appeals of Webster, 47 Mass. App. Ct. at 669.

b. The addition of new nonconformities to a pre-existing nonconforming residential structure requires a variance. Although we conclude that the matter should be remanded to the board, we nonetheless consider whether the Land Court judge correctly concluded that introduction of a new nonconformity to a pre-existing nonconforming residential structure requires a variance, because the question has been fully briefed and argued and because, as noted above, if the Land Court judge was incorrect in his conclusion there would be no need for a remand; the board’s special permit decision alone would be sufficient to allow the Chandler’s project to proceed, without regard to the applicability of § IV.A.3.

As stated above, the new structure will keep many of the preexisting nonconformities of the old structure but, if not exempt under § IV.A.3 of the by-law, it will create an additional nonconformity with respect to height. Consequently, the judge determined that the addition of a new nonconformity required a variance rather than a special permit. The Chandlers challenge this interpretation, arguing that both new and existing nonconformities fall under the purview of a special permit.

“In resolving this dispute, we are again called on to interpret the ‘difficult and infelicitous’ language of the first two sentences of G. L. c. 40A, § 6, as they pertain to single or two-family *548residential structures.” Gale v. Zoning Bd. of Appeals of Gloucester, 80 Mass. App. Ct. 331, 336-337 (2011) (Gale), quoting from Fitzsimonds v. Board of Appeals of Chatham, 21 Mass. App. Ct. 53, 55 (1985). General Laws c. 40A, § 6, provides as follows:

“Except as hereinafter provided, a zoning ordinance or by-law shall not apply to structures or uses lawfully in existence or lawfully begun, or to a building or special permit issued before the first publication of notice of the public hearing on such ordinance or by-law required by section five, but shall apply to any change or substantial extension of such use, to a building or special permit issued after the first notice of said public hearing, to any reconstruction, extension or structural change of such structure and to any alteration of a structure begun after the first notice of said public hearing to provide for its use for a substantially different purpose or for the same purpose in a substantially different manner or to a substantially greater extent except where alteration, reconstruction, extension or structural change to a single or two-family residential structure does not increase the nonconforming nature of said structure. Pre-existing nonconforming structures or uses may be extended or altered, provided, that no such extension or alteration shall be permitted unless there is a finding by the permit granting authority or by the special permit granting authority designated by ordinance or by-law that such change, extension or alteration shall not be substantially more detrimental than the existing nonconforming use to the neighborhood.” (Emphasis added).

The highlighted portion above is often referred to as the second “except” clause. Fitzsimonds v. Board of Appeals of Chatham, supra at 56. To our knowledge, the issue whether existing nonconformities and the creation of new nonconformities should be treated differently under the second except clause of c. 40A, § 6, has not been directly addressed by any appellate court. However, in Gale, supra at 337, this court summarized the general standard for cases concerning the second except clause:

“[U]nder the second ‘except’ clause of . . . the statute, as concerns single or two-family residential structures, the *549permit granting authority must identify the particular respect or respects in which the existing structure does not conform to the present bylaw and then determine whether the proposed alteration or addition would intensify the existing nonconformities or result in additional ones. ... If the answer to that question is in the affirmative, a finding of no substantial detriment under the second sentence is required.” (Quotations and citations omitted.)

Citing the above language, the Land Court judge noted that “ [a]t first blush, it appears this statement in Gale does not distinguish between reconstruction that results in increased existing nonconformities, versus creating new, additional nonconformities.” However, after careful review of the relevant case law, the judge concluded that while intensifying existing nonconformities requires a special permit, the creation of new nonconformities requires a variance. A similar review of relevant cases also is helpful here.

In Gale, supra, we determined that the reconstruction of a pre-existing nonconforming residential structure required a special permit to increase or intensify a pre-existing nonconformity. There, the plaintiffs appealed from the entry of summary judgment dismissing their challenge to the board’s grant of a special permit to the defendant, their neighbor. Id. at 332. The defendant’s proposed new structure had a larger footprint than the previous structure and increased the setback nonconformities. Ibid. This court upheld the entry of summary judgment, concluding that the board’s grant of a special permit, based upon its finding of no substantial detriment to the neighborhood, was all that was required. Id. at 337.

Prior to Gale, in Bransford v. Zoning Bd. of Appeals of Edgartown, 444 Mass. 852, 853 (2005), Justice Greaney, in a concurring opinion of an equally divided Supreme Judicial Court, determined that only a special permit, with the requisite finding that the proposed structure was not substantially more detrimental to the neighborhood, was required to increase or exacerbate an existing nonconformity.16 There, the plaintiff wanted to build a *550new house which conformed to the zoning by-law’s structural requirements, but nonetheless doubled the size of the old structure on a undersized nonconforming lot. Id. at 853-854. Because the expansion of the structure’s footprint on an undersized lot exacerbated the nonconformity, the court found that a finding of no substantial detriment was required under the second sentence of § 6. Id. at 861-862. The court then upheld the board’s denial of a special permit as it was within the board’s discretion to find that the new structure was substantially more detrimental to the neighborhood. Id. at 862.

Therefore, as the Land Court judge noted, “in Gale and Bransford, the Appeals Court and the Supreme Judicial Court, respectively, were faced with the issue of an extension to a preexisting nonconformity and those courts properly limited their final holdings to such circumstances.” See Gale, supra at 338 (“Bransford holds that exterior alterations or reconstructions of single or two-family residential structure that increase or intensify any pre-existing nonconformities may be authorized by means of a finding of no substantial detriment under the second sentence of the first paragraph of § 6”). Nonetheless, some confusion arises from the seminal formulation of the operation of the second except clause articulated in Willard v. Board of Appeals of Orleans, 25 Mass. App. Ct. 15, 21-22 (1987): “[T]he [second ‘except’ clause] should be read as requiring a board of appeals[17] to identify the particular respect or respects in which the existing structure does not conform to the requirements of the present by-law and then determine whether the proposed alteration or addition would intensify the existing nonconformities or result in additional ones.'’’’

It is important to observe at this juncture that the second “except” clause is directed to differentiating between those changes to nonconforming residential structures that may be made as of right, and those that require a finding of no substantial detriment under the second sentence of § 6. Bransford, for *551example, was concerned principally with determining whether a particular change “increased the nonconforming nature” of the residential structure at issue. 444 Mass, at 857. In the present case, it is undisputed that the new structure will increase the nonconforming nature of the old structure. The question, then, is not whether the second “except” clause authorizes the Chandlers’ project as a matter of right, without a finding of no substantial detriment, but whether a finding of no substantial detriment under the second sentence of § 6 may authorize the creation of new nonconformities in a pre-existing nonconforming structure. Although we are aware of no appellate case resolving that question in the context of a residential structure, the Supreme Judicial Court has twice concluded that the creation of a new nonconformity in a pre-existing commercial structure requires a variance.

In Rockwood v. Snow Inn Corp., 409 Mass. 361, 362, 370 (1991), the board of appeals granted the defendant a special permit to extend two prior nonconforming structures, which were nonconforming as to setback. Id. at 362. However, in addition to the setback violation, the proposed new structures also violated the by-law’s lot coverage requirement. Ibid. Because the violation of the lot coverage requirement created a new, additional nonconformity, the court reversed the grant of the special permit. Id. at 370. In reaching its conclusion, the court observed that the first sentence of § 6 provides that the existing by-law “shall apply” to any extension, reconstruction, or alteration of a pre-existing nonconforming structure. Accordingly, the court concluded, the authority to alter an existing nonconforming structure upon a finding of no substantial detriment under the second sentence of § 6 can apply only to changes which themselves conform to the existing by-law, and then only if they are not substantially more detrimental to the neighborhood. In reaching its conclusion, the court observed that “even as to a single or two-family residence, structures to which the statute appears to give special protection, the zoning ordinance or by-law applies to a reconstruction, extension, or change that ‘would intensify the existing nonconformities or result in additional ones.’ ” Id. at 364, quoting from Willard, 25 Mass. App. Ct. at 22.

*552To similar effect is Wrona v. Board of Appeals of Pittsfield, 338 Mass. 87, 89-90 (1958), a case decided under the prior version of c. 40A.18 In that case, the Supreme Judicial Court determined that a planned extension to a motor freight terminal that was both a pre-existing nonconforming use and structure required a variance. There, the defendant received a special permit to build an extension to his motor freight terminal located in a single residence district. Id. at 87-90. The Supreme Judicial Court, however, reversed because the defendant’s proposed extension also violated the by-law’s setback requirements. Id. at 89. Thus, the court concluded that “[t]he board could properly have allowed an extension of the nonconforming use up to the setback lines . . . [hjowever when it permitted the extension beyond the very precise setback requirements contained the ordinance it exceeded its authority.” Ibid.

Applied strictly to residential structures, the holding in Rock-wood would require a variance even for extensions of existing nonconformities; its holding is that “[i]f the first and second sentences [of c. 40A, § 6,] are read together, the statute permits extensions and changes to nonconforming structures if (1) the extensions or changes themselves comply with the ordinance or by-law, and (2) the structures as extended or changed are found to be not substantially more detrimental to the neighborhood than the preexisting nonconforming structure or structures.” Rockwood v. Snow Inn Corp., 409 Mass, at 364. However, a long line of cases, notably including Bransford and Bjorklund, have held that an alteration which intensifies an existing nonconformity in a residential structure may be authorized under the second sentence of § 6 upon a finding of no substantial detriment. See Gale v. Zoning Bd. of Appeals of Gloucester, 80 Mass. App. Ct. at 338, distinguishing Rockwood v. Snow Inn Corp., on the ground that it dealt with a commercial structure rather than a residential one.

As the Supreme Judicial Court made clear in Bransford, 444 *553Mass, at 859, “the ultimate objectives of zoning would be furthered by the eventual elimination of nonconformities in most cases.” (Citation omitted.) See Strazzula v. Building Inspector of Wellesley, 357 Mass. 694, 697 (1970), cert, denied, 400 U.S. 1004 (1971) (considering eventual elimination of nonconforming uses as an objective underlying zoning regulations). As the plaintiffs observe, the fallacy of the Chandlers’ contention that an alteration creating a new nonconformity may be authorized upon a finding of no substantial detriment is illustrated by contrasting a landowner with a conforming structure who wishes to construct an addition that violates the applicable setback requirements (which would require a variance) with a neighboring landowner with a nonconforming structure as to height who also wishes to construct an identical addition, also encroaching to the same extent into the required setback (which, according to the Chandlers, would require only a finding of no substantial detriment). Such a result is illogical, given the significantly more stringent burden for a variance, which is granted “only in rare instances and under exceptional circumstances,” Blackman v. Board of Appeals of Barnstable, 334 Mass. 446, 450 (1956), quoting from Hammond v. Board of Appeals of Springfield, 257 Mass. 446, 448 (1926), compared to the lesser burden for a special permit. See Kiss v. Board of Appeals of Longmeadow, 371 Mass. 147, 153-154 (1976), and cases cited therein. “If a sensible construction is available, [a court] shall not construe a statute to make a nullity of pertinent provisions or to produce absurd results.” Flemings v. Contributory Retirement Appeal Bd., 431 Mass. 374, 375-376 (2000). Like the Land Court judge, we construe the provisions of the first and second sentences of § 6 together to allow extension of existing nonconformities upon a showing of no substantial detriment, but to require a variance for the creation of any new nonconformity.19

Conclusion. For the reasons expressed above, the judgment *554granting the plaintiffs’ cross motion for summary judgment and the order denying the Chandlers’ motion for reconsideration are vacated. The matter is remanded to the Chatham zoning board of appeals to determine whether the Chandlers’ proposed new structure is eligible for the exemption provided under § IV.A. 3 of the Chatham by-law from otherwise applicable height limitations.

So ordered.