Appellant and appellee are the several owners of adjoining 1-ots in the city of Pine Bluff, and each lot is -covered by -a brick building. The buildings were each originally one-story -in height, and the north wall of plaintiff’s building was used by the owner of the -other building .as its south wall. Subsequently appellee added another story to her building. Appellant is now about to add -another story to h-is building, and claims the right, in so doing, to use the upper wall constructed by appellee. This suit was instituted by appellee against ap*151pellant to restrain him from -cutting into the upper wall, or using it in any -way.
It is alleged in the complaint that the wall is entirely upon plaintiff’s lot, and the evidence show-s this to -be true except that the footing -or foundation of the wall extends about six inches over on defendant’s lot. Defendant purchased his property from the heirs of one Myer Greenblatt, • and he relies upon an instrument of writing alleged to have been executed as a contract between plaintiff and Greenblatt.
The instrument in question is as follows:
“State of Arkansas.
■ “This is to show that whereas Mrs. Mary A. Parse and Myer Greenbl-att -own two adjoining one-story brick stores fronting Main Street in block 21 of Pine Bluff; now for certain valuable considerations it is agreed -that if either Mrs. Parse or Greenblatt desires to make their respective store houses two stories high, either party shall have the right to build a second-story wall on the present dividing wall. This agreement to continue while the present wall stands and no longer, and without prejudice to -the title of either party to the land occupied .by the wall. If one party build the wall, the other shall have the right to use.
“Witness the hands and -seals of Mary A. Parse and Myer Greenblatt, this March 30th, 1883.
[Signed] “Mary A. Parse."
The instrument was not signed by Greenblatt. When it was signed by -the plaintiff, Mrs. Parse, both buildings had been erected, the wall of plaintiff’s building having been used in constructing the Greenblatt building. The terms or agreement, if any, upon which the wall was used is not -disclosed by the evidence. The plaintiff erected the second story of her building in the year 1890. She testifies that no consideration was paid to her for signing the instrument in question, that it was brought to her for her signature -under the agreement o.r understanding ■that it was -to be signed -also by Greenblatt, that she had not since seen the paper nor heard of it until this controversy arose-when defendant attempted to use the wall of the upper story. Greenblatt is dead, and the defendant Trulock testifies that the *152paper was delivered to him by the Greenblatt heirs when they sold him the property.
The defendant also contends that the wall is partly on his lot, and that he has a right to use it as a party wall, out the evidence is against him on this issue. It shows that the wall is on the plaintiff’s lot. It is true that the footing or foundation of the wall extends about six inches over defendant’s lot, but this does not make it a party wall. The extension is not above the ground, and would not interfere with defendant in building a new wall on his own lot. Learned counsel for appellant invoke a doctrine which has been announced that where an owner of a lot constructs a building thereon so that the wall thereof projects over on an adjoining lot, he cannot, without removing the projection, deny the owner of the adjoining lot the right to use it. 1 High on Injunctions, § 783; Guttenberger v. Woods, 51 Cal. 523. This is upon the ground that to permit the 'obstruction to remain without allowing the adjoining owner the right to use the projecting wall would be to deny him the free use of his own property. But this doctrine does not apply where the projection does not prevent or obstruct the free use of the adjoining property by its owner. The six-inch projection underneath• the surface of the ground did not interfere with defendant’s free use of his property in erecting a wall on the edge of his lot; at least, the evidence does not show any interference. The mere fact that the foundation was partly on defendant’s lot did not give him the right to use a wall entirely on plaintiff’s lot above the surface of the ground.
Is the plaintiff bound by the written instrument which she signed, notwithstanding the fact that it was not signed by the other party? It will be seen that the contract is unilateral, and primarily imposes obligations on only one of the parties— Mrs. Parse. According to its terms, she granted to the other party named therein the right to build a second-story wall on condition that she be permitted to use it, and granted to him the right to use the second-story wall if she should build it. He did not obligate himself to build the wall or to do anything else. Therefore there was no necessity for his signature to the instrument. The provisions being entirely for his benefit, his receipt and retention of the writing, even without sign*153ing it, imported an acceptance of its terms. 29 Am. & Eng. Enc. Law, 858, and cases cited. His signature would have added nothing, inasmuch as the writing itself did not impose an obligation upon him. He undertook nothing under the contract as written except to allow plaintiff the use of the second-story wall in the event he chose to built it. If the plaintiff could be held at all upon the contract, we think that the failure of the defendant to attach his signature to it did not, under the circumstances of this case, affect the question of her liability.
But there was no consideration fo,r the contract, and for that reason the plaintiff is not bound to perform it. The wall being entirely upon the plaintiff’s lot, her agreement to permit plaintiff to use the second-story wall in the event that she should erect it was a mere gratuity, a nudum pactum. The evidence shows that there was no consideration at all. Mutual promises or undertakings constitute sufficient consideration to support a contract, but this contract contained no promise or undertaking on the part of G.reenblatt. His promise to allow plaintiff to use the wall in the event he chose to erect it was not sufficient consideration for her executory contract for the use of the wall. Mutual promises 'or undertakings, in order to constitute of themselves consideration for a contract, must be concurrent so as to become obligatory at the same time. 9 Cyc. 325. Of course, if Greenblatt or his successors in title had proceeded to build the second-story wall in accordance with the contract, the writing would have become mutually binding upon both parties; but, as long as nothing was done .under it, the contract was, fo.r want of consideration, nugatory and without binding force upon plaintiff. Until something was done under it by the other party, it was a mere proposal or option which she had the right to withdraw.
Suit for injunction was the proper remedy against the defendant’s attempted encroachment upon the property. 22 Cyc. 834.
We think the chancery court reached the correct conclusion in the case, and the decree is affirmed.