The Commonwealth’s lodging house licensing statutory system — G. L. c. 140, §§ 22-32 (Act) — is at the center of this consolidated appeal. Five property owners (defendants) appeal from judgments of the Housing Court permanently *758enjoining them “from allowing more than three unrelated adults to reside in each legal dwelling unit” in question, and from final orders adjudging them in contempt for disobeying court orders so enjoining them. General Laws c. 140, § 22, amended by St. 1973, c. 481, defines a lodging house as “a house where lodgings are let to four or more persons not within the second degree of kindred to the person conducting” such a facility.

On appeal, the defendants argue the order for injunctive relief was erroneous as matter of law and must be vacated. They contend each unit was rented to four unrelated adult college students, living as a “family” or single housekeeping unit, an arrangement which, the defendants say, does not constitute a lodging house under the Act. We affirm.

1. Background. The facts, which are not in dispute, are as follows. The defendants own multiunit rental properties in the city of Worcester (city). Paul F. Giorgio and Diana H. Giorgio own such properties at 7 Clay Street and 13 Boyden Street. College Hill Properties, LLC, an entity controlled by Paul F. Giorgio, owns a property located at 11 Boyden Street. Michele Meaney and Paul J. Meaney own properties at 21 and 23 Caro Street.

Upon an investigation by its department of inspectional services, the city served the defendants with written notices, citing them for operating unlicensed lodging houses at the stated locations. The city ordered the defendants to cease and desist from doing so; the defendants refused.

As authorized by G. L. c. 140, § 24,3 the city commenced civil actions against the defendants to enforce its administrative orders and made application to a Housing Court judge for the issuance of preliminary injunctions restraining the defendants from conducting unlicensed lodging houses.4 See Mass.R.Civ.P. 65(b)(1), 365 Mass. 832 (1974).

The city presented evidence showing that at each property *759address, the defendants rented a unit to four unrelated adults, all of whom were students at a local college. Each unit had a living and dining room, kitchen, bathroom, and bedrooms (the number of which was left undefined). Counsel for the defendants represented to the judge that the students signed a lease for a twelve-month period; no lease was offered to the judge.

After a hearing in each case, the judge granted the city’s application and issued an injunction commanding the defendants to “forthwith reduce the number of unrelated adult occupants” in the subject premises “to no more than three in each legal dwelling unit.”5 There the cases stood until the city filed civil contempt complaints against the defendants for disobeying the injunction. See Mass.R.Civ.P. 65.3, as appearing in 386 Mass. 1244 (1982).

Show-cause hearings ensued. The judge found the defendants in contempt and imposed fines,6 memorialized in the judge’s orders of contempt. Final judgments entered permanently enjoining the defendants “from allowing more than three unrelated adults to reside in each dwelling unit.” The actions were later consolidated for purposes of this appeal.

2. Standard of review. Action by a licensing body in furtherance of the Act is appraised by the substantial evidence test. See G. L. c. 140, § 30; Trustees of Paul Revere Realty Trust v. Revere License Commn., 29 Mass. App. Ct. 11, 12 n.3 (1990). This case reduces to a question of law as to the meaning of “lodging house” under the Act, an issue that is subject to de novo review. See Massachusetts Insurers Insolvency Fund v. Smith, 458 Mass. 561, 564-565 (2010); Commonwealth v. B & M Fitzgerald Builders, Inc., 71 Mass. App. Ct. 486, 491 (2008); Gore v. Arbella Mut. Ins. Co., 77 Mass. App. Ct. 518, 536 (2010).

“[W]e interpret the words used in a statute with regard to both their literal meaning and the purpose and history of the *760statute within which they appear.” Atlanticare Med. Center v. Commissioner of the Div. of Med. Assistance, 439 Mass. 1, 6 (2003), quoting from Massachusetts Hosp. Assn. v. Department of Med. Sec., 412 Mass. 340, 346 (1992). We concur with the judge that under the Act, “lodging house” encompassed the arrangements the defendants had obtained with the students, resulting in violations of the law.

3. Discussion, a. Lodging house. The Legislature’s licensing system for regulating lodging houses in the Commonwealth was enacted during World War I. St. 1918, c. 259. It was designed to address the Legislature’s concerns with the deplorable health and sanitary conditions then prevailing in lodging houses and their notorious use as a venue for immoral solicitation and other like conduct. See Maher v. Brookline, 339 Mass. 209, 215 (1959); Newbury Jr. College v. Brookline, 19 Mass. App. Ct. 197, 203-204 (1985). “It is unquestioned that the Legislature has inherent authority to regulate buildings, structures and premises in the interests of public safety, health, morals and welfare.” Inspector of Bldgs. of Falmouth v. General Outdoor Advertising Co., 264 Mass. 85, 87 (1928).

The policies generally advanced by the Act still hold today with respect to the common practice of overcrowding persons in an unsuitable space, whether in lodging houses or tenements. Tenant overcrowding and fire protection were among the reasons the city cited for its enforcement actions. To obtain a lodging house license, an applicant must have sprinkler systems in the premises. The defendants do not claim to have sprinklers in their units.7 See Massachusetts Sober Hous. Corp. v. Automatic Sprinkler Appeals Bd., 66 Mass. App. Ct. 701, 704-705 (2006).

Because safety, health, and welfare concerns stemming from lodging houses have more to do with management than with *761zoning issues, licensure is an effective regulatory device to bring about desired legislative ends.8 “Licensing serves a triggering function, to alert local authorities that they should monitor conditions in the licensed premises.” Newbury Jr. College, supra at 205.

With this backdrop, we look to the words of the Act itself.9 Lodging house is “a house[10] where lodgings[11] are let[12] to four or more persons not within second degree of kindred to the person conducting it.”13 G. L. c. 140, § 22. The city’s proof established each such element for each of the properties at issue here: a building or structure, where housing accommodations are leased or let, to four adults, unrelated to the defendants.

As they did before the judge, the defendants contend that their properties are not governed by § 22 because each unit was occupied by four or more unrelated adult tenants, “living as a family unit,” not lodgers.14 This argument was also advanced in *762Worcester v. Bonaventura, 56 Mass. App. Ct. 166 (2002), and this court rejected it.

Bonaventura, which is virtually identical to the present appeal, involved enforcement actions by the city against owners who had rented condominium units to four unrelated adults, all of whom were students at a local college. Each student had signed a lease, was jointly responsible for the rent, and had full use of the unit. Id. at 167. There, as here, the defendants had argued the students were tenants whose living arrangements formed a single housekeeping unit, akin to a family, within the meaning of a local zoning ordinance.15 That argument was unpersuasive. We held that the question whether the owners were operating a lodging house did not “turn on the status of the student occupants as tenants,” but that it was a legal issue for the court to answer by interpreting the terms of the local zoning ordinance “in the context of the [ordinance] as a whole and, to the extent consistent with common sense and practicality, [giving them] their ordinary meaning.”16 Id. at 168. The same is true here, except the Act, not a local ordinance, is at issue.

*763The Act, we believe, covers such an ad hoc group housing arrangement, among four or more persons, whose composition is not a family or single housekeeping unit, and which is not otherwise licensed or regulated by State agencies. Though the line between a lodging house, single housekeeping unit, and group home may not always be easy to discern, see Hall v. Zoning Bd. of Appeals of Edgartown, 28 Mass. App. Ct. 249, 256 n.9 (1990), we have no doubt that four or more unrelated adults, sharing housing while attending college, is not an arrangement that lends itself to the formation of a stable and durable household.

It is enough to say that the city, in its licensing capacity, reasonably exercised its supervisory and enforcement powers to remedy an unsafe and illegal condition existing in the subject properties. To narrow the definition of lodging house, as the defendants ask us to do, would undermine the Act’s purposes: to assure such facilities are safe, sanitary, habitable, and orderly. And, to do so, absent a mandate from the Legislature, would likely offer a blueprint for property owners to circumvent this long-standing licensing system.17

The judge properly issued the injunctive relief enforcing the city’s administrative order based on the city’s proving all of the statutory elements of a lodging house.18 See Packaging Indus. Group, Inc. v. Cheney, 380 Mass. 609, 615-616 (1980). His findings are supported by substantial evidence in the record, and his ultimate ruling determining the meaning of “lodging house” is not marred by legal error. See Jaffe, Judicial Enforcement of Administrative Orders, 76 Harv. L. Rev. 865, 866 (1963) *764(“The core of the judicial function where enforcement is in question is the determination of legality”).

b. Civil contempt. In each action here,19 the city filed a complaint requesting the judge to find the defendants in civil contempt, Mass.R.Civ.P. 65.3, for failing to comply with the preliminary injunction. The defendants answered and denied the allegations. Hearings ensued on April 14, 2010. The defendants argued they tried to comply but were stymied due to roadblocks attendant to the leases.20 The judge found them in contempt. “To constitute civil contempt there must be a clear and undoubted disobedience of a clear and unequivocal command.” United Factory Outlet, Inc. v. Jay’s Stores, Inc., 361 Mass. 35, 36 (1972). See Birchall, petitioner, 454 Mass. 837, 852 (2009). The city had the burden to prove the defendants’ undoubted disobedience of the injunction by clear and convincing evidence. It did so, and the judge correctly found as much. Nor was there any error in sanctioning them as the judge did here.

When announcing the fines during the April 14 proceedings, the judge made it known to the parties, in no uncertain terms, that he would hear them on vacating the fines if compliance was had by April 21, 2010. That did not occur, and the judge had no occasion to act on a request to erase the fines. On this record, there is no basis to do other than uphold the contempt orders.

The final judgments and orders of contempt are affirmed.

So ordered.