In 1958, plaintiffs purchased land in defendant city desiring to subdivide the property into residential lots. At the time of the purchase the city had in force and effect a comprehensive zoning ordinance which would, when applied to the subject land, restrict the lots to a minimum of 30,000 square feet in area. Each lot was to he not less than 150 feet in width and not less than 200 feet in depth. The plaintiffs wanted to subdivide their property into lots of over 100 feet in width, with an average depth of 150 feet, each lot thus containing about 15,000 square feet.
The request for rezoning was denied and this cause was instituted. Plaintiffs were granted a decree on the pleadings and the pretrial procedure. Motion for rehearing was denied. On appeal we determined the trial court had erred and remanded *96it to the trial court for the taking of proofs. Upon completion,’ the trial court decreed:
“that section 14 ,of Ordinance No 23 of the city of Troy, Oakland county, Michigan, insofar as it pertains to the property of the plaintiffs as hereinafter described, is an unwarranted and illegal extension of the police power of the city and is unreasonable and void, and * * *
“that the plaintiffs shall be, and they are hereby, authorized and empowered to use the said property for a residential subdivision in accordance with the proposed plat attached to plaintiffs’ bill of complaint and there marked exhibit A; provided, however, that the plaintiffs shall, at all times, comply with all other valid existing ordinances of the city of Troy and with the statutes of the State of Michigan applicable to the platting and use of said land.”
This same zoning ordinance, and section, but a different classification, was before the Court in the recent case of Christine Building Company v. City of Troy, 367 Mich 508. Many of the facts in that case and the questions posed are identical to the ones in the case at bar, and to the extent that they are identical, they are controlled by the decision in Christine. It must be noted that the Court is cognizant that 1 of the basic rules for testing the reasonableness of a zoning ordinance provides that the determination must be made in the light of the facts presented in each case. “Each zoning case must be determined upon its own facts and circumstances.” Moreland v. Armstrong, 297 Mich 32, 36; Senefsky v. City of Huntington Woods, 307 Mich 728, 737 (149 ALR 1433).
Other principles to be employed reviewing the constitutionality of zoning ordinances have been set out in detail in Christine and cases cited therein and we see no need for repeating them now.
*97Plaintiffs contend that the' zoning restriction of 30.000 square feet minimum as applied to their proposed platted subdivision “is unreasonable as it bears no substantial relationship to present public health, safety, morals or general welfare, and is confiscatory and discriminatory.” In support of their claim, plaintiffs produced witnesses who testified in substance that the proper protection of health, welfare, and safety does not require compliance with the 30,000 square foot minimum. Without quoting specific testimony, these witnesses, who were experienced in the developing and marketing of subdivisions, and of appraising land and buildings, claim that substantially smaller lots would he ample to satisfy proper requirements as to health, sanitation, safety, and welfare. They testified further that there would he no harm or damage to the surrounding area by building on 15,000 square foot lots; that there would be no detrimental effect in the overall zoning plan of the entire city; that the change to 15.000 square feet minimum would bring the property in question in line with property immediately adjacent to the east and to the south; and that other property surrounding the plaintiffs’ did not come up to the present minimum zoning requirements. Proofs also showed that other property close to that of plaintiffs had been rezoned from a minimum size area of 30,000 square feet to 15,000 square feet. Testimony tended to show that the plaintiffs’ property today, as presently zoned, was not worth the amount paid for it, and that this zoning requirement would make it economically unsound to develop the property. It is true that “mere depreciation in value by itself is not enough. The test is whether the zoning classification is unreasonable.” (Emphasis supplied.) Moreland v. Armstrong, supra, 36; City of Howell v. Kaal, 341 Mich 585, 590.
*98To support their position that the ordinance was a valid exercise of legislative power, the city asserts the following:
“A. The mere disparity in value of property resulting from the adoption of a zoning ordinance is insufficient to establish that such ordinance is unreasonable, especially where the owner of the property admittedly paid an excessive price for said property in anticipation of a change in zoning that would increase the value of the property.
“B. The present zoning, as applied to the subject parcel, tends to preserve the established character of the neighborhood, stabilizes the value of property therein and promotes the general welfare.
“C. The minimum lot size requirement of 30,000 square feet, as applied to the subject parcel, constitutes an integral part of the comprehensive zoning plan of the city of Troy and therefore bears a real substantial relation to the public health, safety and general welfare.
“D. Comprehensive zoning plan of the city of Troy, as applied to the subject parcel, promotes the orderly development of the city and safeguards the city’s economic structure.
“E. Present zoning of the subject parcel will create the maximum density of population that can be serviced by available sanitary sewers.”
Nothing in the majority opinion in Christine should be construed as indicating that this Court is insensitive to the need for comprehensive municipal zoning plans, but these, like all others, must meet the test of reasonableness.
"With regard to the available sewage disposal system, defendant’s witness, a civil engineer, stated that, •at the present, there was sufficient sewer capacity to meet the needs of the plat proposed by plaintiffs but that if present zoning were not maintained, overloading of sewer facilities might occur at some later date. (The sewage system was the same Ever*99green interceptor discussed in Christine, capable of serving 21,300 people in 6,000 bousing units. At the time of trial there was a small fraction of the anticipated population, and “Roughly a thousand units”.)
The trial judge found that “the plaintiffs have-overcome the presumption favoring the city of Troy,, and that the plaintiffs by a fair preponderance of the evidence and proofs have clearly established there is no real need for this zoning and * * * the plaintiffs have clearly proven that under the present conditions it is unconstitutional.”
We are in accord with the finding of the trial judge and conclude that the section of the ordinance as applied to plaintiffs’ property is unconstitutional.
One other question remains to be considered: “Where the court has decided that a provision of the municipal zoning ordinance covering the zoning of a minimum lot size is unreasonably large and therefore void, does it then have the right to assume the role of a municipal legislator and impose upon the subject parcel a smaller lot size?”
As can be seen from the decree of the trial judge hereinabove set out, plaintiffs were empowered to use their property in accordance with the proposed plat, therefore the minimum size was established at 15,000 square feet.
This Court agreed with the trial judge in Christine 515, 516, that he had no legal duty, right, or obligation to undertake to pass upon the reasonableness of proposed zoning that is not yet the subject of an ordinance. Recognizing that zoning is a legislative function we affirm the principle that courts cannot write zoning laws. The trial court’s decree is modified by striking therefrom that portion authorizing and empowering plaintiffs to use the property as proposed in the plat. In all other respects the decree is affirmed. No costs, neither party having-prevailed entirely.
*100Carr, C. J., and Dethmers, Kelly, Black, and Kavanagh, JJ., concurred with Smith, J.