Our review of zoning board of adjustment decisions is limited to questions of law and legal inference; we may not consider questions of fact. G.S. 160A-388(e); Coastal Ready-Mix Concrete Co. v. Board of Commissioners of the Town of Nags Head, 299 N.C. 620, 265 S.E. 2d 379, reh. denied, 300 N.C. 562, 270 S.E. 2d 106 (1980). A Board’s findings of fact if supported by competent evidence are conclusive on appeal. In re Campsites Unlimited, 287 N.C. 493, 215 S.E. 2d 73 (1975). The Board’s findings of fact in this case are so supported, but neither the findings nor the record as a whole support the conclusion that petitioner is violating the zoning law of the City of Rocky Mount by permitting her son and his family to occupy the dwelling house involved.
*230In the first place, the record that respondent Board certified to the court, all that we have to go by in determining the validity of its action, is quite incomplete. It contains only selected parts of the zoning ordinance petitioner is allegedly violating and no part of the earlier ordinance that was in effect when the house involved was built, or at least when the City gave the former owner a permit to build it. For the record shows that the house was built under a permit issued by the City of Rocky Mount on 24 April 1975, whereas the zoning ordinance petitioner is charged with violating was not enacted until several months later and did not become effective until 1 January 1976. Too, while the building permit shows that the lot was then classified R-15 (it is now classified R-10), the record does not tell us what that classification entailed; it merely shows that the former owner was authorized to construct an “accessory building.” But what an “accessory building” under the former ordinance was and what use it was limited to we do not know. It is self-evident, though, that the house was built for human habitation and the record does establish that it was so used for several years before petitioner bought it; but whether those that used it were required to be domestic employees of the former owner we do not know and refuse to surmise that they were. It is rudimentary learning, though, that a later enacted zoning ordinance does not affect the use of existing buildings or those that are being constructed under a lawful permit. Town of Hillsborough v. Smith, 276 N.C. 48, 170 S.E. 2d 904, 49 A.L.R. 3d 1 (1969). Thus if the house when it was built or started could be lawfully occupied by the owner’s, child and his family, and nothing in the record suggests that it could not, the limitation later enacted would have no application. In all events we cannot conclude from this record that petitioner is in violation of the City zoning ordinance by permitting her son and his family to occupy the dwelling house involved, and therefore vacate the judgment appealed from.
In the second place, if we interpreted the zoning ordinance excerpts brought forward to prevent petitioner’s son and his family from occupying the house situated in her backyard, but to authorize a domestic employee and his family to live there, as the respondent contends that we should, we would be obliged to hold that the ordinance is unconstitutional. This is because an inherent requisite of all legislation is that it be rationally related to a pur*231pose that the enacting body is authorized to address and if there is a rational relation between prohibiting a property owner’s child from living in a dwelling house on her property that is zoned for residential purposes and any object of the police power, which is the basis for all zoning legislation, it is not apparent to us. Nor have we found any court decision involving similar circumstances that so holds. Certainly the ordinance cannot promote low density occupancy of the lots involved, a proper object of residential zoning, as it permits an extra family to live on each lot classified R-10 and limits only the status of the extra occupants. In this instance, it is not as if family residential property was being used for another purpose, say as a nursing or retirement home, as in In re Appeal of McGinnis, 68 Pa. Commw. 57, 448 A. 2d 108 (1982), cert. denied, 461 U.S. 944 (1983); the property here is being used for the residential purposes that the ordinance requires. Nor is it as if those using the house were different in status or class from other occupants of that area, as in the case of New York v. Renaisance, 36 N.Y. 2d 65, 324 N.E. 2d 355 (1975), where it was fallaciously contended that unrelated narcotic addicts under rehabilitation were “family” members within the meaning of the local ordinance; the user here, along with his family, is the actual child of the owner.
The judgment appealed from is therefore vacated and the matter remanded to the Superior Court for appropriate disposition in accord with this opinion.
Vacated and remanded.
Judge Becton concurs.
Chief Judge HEDRICK dissents.