delivered the opinion of the Court:
The points relied on by appellant are four. We shall consider them separately, but not in the order stated by him. First: lie asserts that there is error in the exclusion of certain testimony offered by him for the purpose of showing* that the appellee had erected a party wall on the south line of her property long before he had attempted to construct one on the north line. In view of the conclusion which we have reached on the whole case, it is not necessary to pass upon this.
Second: Was appellee silent when she should have spoken, as appellant charges ? The argument of appellant with respect to this is based chiefly on certain correspondence which passed between G'eorge 0. Totten, Jr., the architect and agent of the appellant, and Mrs. Boyts, who was at Connellsville, Pennsylvania, at the time. Mr. Totten wrote to her that he had “just made1 drawings for an addition to Mia T. T. Mann’s residence,” and that the addition would “extend to the party line between your property” and his; he stated that according to his drawings, the moldings and cornice of the addition would extend over her property “perhaps a foot,” and asked her to consent to the extension, .lie inclosed a draft of a letter giving consent and addressed to the building inspector, for her signature; and added that if she refused, Mr. Mann had the right to build the wall “centered on the party line.” She promptly declined to consent and so notified Mr. Totten by letter, which he admits receiving. None the less, the appellant constructed a Avail not extending “to the party line between” the properties, but reaching over the line oyj inches. She had no knowledge that he was 'doing so until July 26, about two months after she had Avritten her letter of refusal, Avhen, after her return to Washington, she discovered that the wall Avas nearly finished. This is all upon the subject. She had a right to assume that Totten was telling her the truth, AA’hen he said that the drawings contemplated a Avail which Avould go to the “party line” only, except- the cornice and moldings; and it docs not lie in his mouth or that, of his principal to say now that because she did, she is estopped from challenging the validity of an act which she *360knew nothing about until after it had taken place. Refusal to consent to one thing does not in itself establish consent to something else. If estoppel is to be applied to anyone it should be to the appellant, whose agent, Totten, lulled plaintiff into the belief that he would not build a party Avail.
Third: We uoav come to the most difficult phase of the case. Did the appellant have the legal right, under the circumstances disclosed by the record, to erect the Avail in controversy? Both lots Avere improved. The plaintiff had upon hers a spacious brick dwelling house, four stories and basement high, containing about twenty-five rooms, built in 1SS7 and occupied by her as a residence. It Avas valued at $40,000. The building Avas so erected that there Avas a space of over 40 feet between it and the sidewalk. Between it and the property of the defendant was a concrete Avalk running the full depth of the building, 74 feet. On the second story, north side, about midway the length of the building, Avas an oriole octagon bay AvindoAv projecting aborit 8 feet, 5 inches, from the main dwelling and leaving a space of 5 ¿4 inches between its outer edge and the defendant’s lot line, except that there were a cornice and trimmings upon the AvindoAvs which extended to the party line.
The defendant’s building, occupied by him as a home, was constructed in 1881, six years before plaintiff’s. It also stood about 40 feet back from the sideAvalk. The south Avail, that is, the one next to plaintiff’s, run back 76 feet and was about 26 feet north of the party line, or a little more than 80 feet from plaintiff’s building. This Avas the relative situation of the respective properties of the litigants at the time Hr. Mann entered upon the construction of an addition to his house, Avhicli when built had as its south Avail the one in dispute. This addition, consisting of tAvo stories and a basement, commenced 17 feet east of the front of his house and ran back only about 27 feet. It extended south 26 feet, 5->d inches, and onto the plaintiff’s property. In other Avords, the addition consists of a tAvostory projection approximately 26 x 27 feet, reaching from about the center of defendant’s building to and across the party line. To make room for the party Avail, defendant removed *361the cornice, sill, and other parts of plaintiffs oriole window. The Avail completely blanketed the north side of the window, and thereby shut off the air and light Avhich otherwise would, have passed through it into plaintiff’s house. There were 34-feet of glass area thus darkened, leaving but two small windows in the oriole window, one on the east and one on the west, having-each a glass area of about 7 square feet. This resulted in making the center room of the house, “formerly a beautifully light room,” so dark that “it cau only be used bv artificial light.” There is testimony of experienced builders that plaintiff could not use the parly wall, it being- only 13 inches thick, “without reinforcing it with steel,” and in no event Avithout removing her north wall, which would require “supports under the present Avooden joists, winch would be a A-ery expensive operation.” It Avas also shown that plaintiff’s house Avas 58 feet 10 inches high, and that under the building- regulations the outer Avail of such a house for the first story should be 18 inches, and that hence the party wall could not be used without increasing its thickness. The testimony further disclosed that if plaintiff moved her north Avail, she could not use the entire 27 feet of the party wall, because the building regulations Avould require her to maintain au air and light shaft between her house and the addition 5 feet wide, and not less than 10 feet long, thus preventing her from utilizing more than 17 fed of that Avail. Mr. Totten said (hat the reason for building the party Avail Avas “that it gyve 5 or G inches more space” to defendant's room and made it “brighter.” From this testimony it appears very clearly that the plaintiff lias sustained a very serious injury to her property by reason of the construction of the Avail, and that she could not utilize it to any advantage w-ithout making a radical change in the north side of her house at a-tu-v great expense, — a change Avhich in all probability would destroy the symmetry of the building and result in an architectural hodgepodge.
Defendant predicates his right to appropriate plaintiff’s property Avithout her consent, and build thereon, upon building regulations of the city of Washington made in pursuance of a condition in deeds through which both parties claim. These *362deeds conveyed the land “on and subject to such terms and conditions as shall be thought reasonable, by the President for the time being', for regulating the materials and manner of the buildings and improvements of the lots, generally in the said city, or in particular streets or parts thereof, for common convenience, safety, and order.” Pursuant to this authority, the President of the United States adopted a regulation which provides “that, the person or persons appointed by the Commis.sioners to superintend buildings may enter upon the land of any person to set out the foundation and regulate the walls to be built between party and party, as to breadth and thickness thereof.” That provision was in force when the parties to this litigation acquired title to their respective properties. It does not in specific terms empower an adjoining owner to build upon the property of his neighbor, but, assuming that it does, when may the power be exercised? The deed giving the President the right to prescribe the regulation says that it shall be done “for common convenience, safety, and order.” The power thus conferred, since it authorized one person to take the property of another against his will and without giving any present consideration therefor, must be strictly construed. Smoot v. Heyl, 34 App. D. C. 480. And the Supreme Court of the United States, affirming the decision of this court in the Smoot Case, and construing the power wc are discussing, said: “The fundamental idea is that of mutual benefit.” In Robinson. v. Hillman, 36 App. D. C. 576, this court decided that every wall constructed by an adjoining- owner “in serving his own needs is not necessarily a party wall, within the meaning of the regulations;” that it must be “such a wall as will satisfy the reason and purpose for which the regulation was devised.” And we have just seen that this purpose is the “mutual benefit” of the parties. Mutual benefit, then, is the criterion by which to determine whether or not the power may be exercised. If the. benefit is unilateral, not mutual, the wall may not be constructed. Applying this test to the wall in question, we are not able to say that it constitutes a mutual benefit. On the contrary, we think, as wc have before indicated, it is a positive injury to the appellee. Even the appellant denies that either *363he or his counsel claims the right “to build a party wall simply because there is a physical opportunity to do so.” Thus he admits that the right is not absolute, but limited; and this being so, the problem, difficult to solve, is, What are those limitations ? It is- not practical to enumerate them. Each case must rest 'npon its own facts. Let it suffice to say here that, a party wall may not be erected against the will of the adjoining* owner where he lias already made important permanent improvements suitable to his property and the neighborhood, and the wall, if constructed, would not only materially destroy the enjoyment of his property in its present condition, but would also involve a radical change in the structure of his improvements, and cause, him a large expense without any corresponding benefits to him. Where those conditions appear, as in the present case, it cannot be said that the party wall is for the “common convenience” or the “mutual benefit” of both parties.
Fourth: Appellant demies the jurisdiction of equity, especially the power to grant a mandatory injunction, in this case, and says plaintiff should be remitted to her remedy at law*. Wo cannot, assent to this. The' wall having been erected on plaintiffs land in violation of her rights, equity has ample power to compel its removal. Weeks v. Heurich, 40 App. D. C. 46, 60, Ann. Cas. 1914A, 972. In Haitsch v. Duffy, 10 Del. Ch. 280, 92 Atl. 249, it was said that “'a mandatory injunction may be awarded by a court of chancery to enjoin the continuance of an encroachment [ upon land] and compel a removal thereof” (citing many authorities), and added that the power to do so was “based on the peculiar nature of the right invaded and the subject-matter affected, viz., land.” (See Long v. Ragan, 94 Md. 465, 51 Atl. 181, and Herr v. Bierbower, 3 Md. Ch. 458. The defendant hero went upon the plaintiff’s property wrongfully, and, with full knowledge of her opposition, constructed the wall. Plaintiff cannot he forced to sell her property to him, but equity will compel him to restore the premises, as nearly as may be, to tlieir original condition. Tucker v. Howard, 128 Mass. 361. See also Lynch v. Union Inst. for Sav. 159 Mass. 308, 20 L.R.A. 842, 34 N. E. 364. “Whore one intrudes upon the laud of another, the latter has *364choice of remedies; he may compel a withdrawal of ihe intruder, or he may regard the intrusion as a permanent trespass and recover compensatory damages therefor.” Baugh v. Bergdoll, 227 Pa. 420, 423, 76 Atl. 207; see also Szathmary v. Boston & A. R. Co. 214 Mass. 42, 100 N. E. 1107; Norwalk Heating & Lighting Co. v. Vernam, 75 Conn. 662, 96 Am. St. Rep. 246, 55 Atl. 168; 22 Cyc. 782; Baltimore Belt R. Co. v. Lee, 75 Md. 596, 601, 23 Atl. 901; 5 Pom. Eq. Jur. 833; High, Inj. 704. In Simmons Creek Coal Co. v. Doran, 142 U. S. 417, 449, 35 L. ed. 1063, 1075, 12 Sup. Ct. Rep. 239, where one of the parties had gone as a trespasser upon the land involved in the suit, and then challenged the power of a court of equity to remove him, Mr. Chief Justice Euller said: “It cannot be held that this trespass on appellant’s part constituted a possession which in itself would drive complainant to an action of ejectment.” These cases, and many others that might he cited, show conclusively that equity has power to force the defendant to remove his wall from the property of the plaintiff.
The judgment of the lower court is right and is therefore affirmed, with costs. Affirmed.