delivered the opinion of the Court:

1. The first assignment of error, in proper order, is that founded on the exception taken to the plaintiffs’ evidence of title.

As to the sufficiency of the instruments to show title from the sovereignty of the soil, we need not inquire for two reasons. (1) The evidence introduced by the defendants to prove title showed that Hugh Gelston was the common source off title. (2) Aside from this, the evidence of plaintiffs, in addition, showed that they and their devisor had been in open, undisturbed adverse possession of the premises, including the strip in controversy, for about forty years, under claim of title. Moreover, unless defendants had the right to enter and construct a party wall, they were mere trespassers. The effect of the third' item of the will of Arm. B. Hillman' was to pass to the plaintiffs the fee simple title to lot 227, subject to the charge of the payment of the legacies to her two sons. The evidence shows that this charge had been satisfied without Bale *581of the premises, and the title was unaffected by the provisions of Item 1, relating to sale.

2. It appears that defendants entered upon the plaintiffs’ lot, not under any claim of title to a part thereof, hut for the purpose of constructing one half of the wall of their building thereon.

They claim that the wall is a party wall, and that they had the right to construct one half of it on plaintiffs’ adjoining land, under authority conferred by the building regulations.

These regulations, the validity of which has not been disputed, provide that the owner of a lot, desiring to build thereon, shall have the right to erect one half of his wall upon the" adjoining lot of another, — in no case exceeding 9 inches. The adjoining owner shall have the right to use said wall, or any part thereof, but before doing so, he shall pay the value of the part so used. Assuming the right to enter upon plaintiffs’ lot for the erection of this wall as a party wall, the defendants applied for and obtained the usual building permit, and erected the wall in compliance therewith.

It is settled that every wall that may be constructed by the adjoining owner in serving his own ends is not necessarily a party wall, within the meaning of the regulations. It must be such a wall as will satisfy the reason and purpose for which the regulation was devised. Smoot v. Heyl, 34 App. D. C. 480. On the other hand, if the wall answer the ordinary requirements of a party wall, the right to erect it in part upon the adjoining lot cannot be made to depend upon the intention or ability of the owner of the lot encroached upon to make use of it at the time. Vacant land may be encroached upon for the purpose. The regulations are intended to. serve a good purpose, and necessarily contemplate future growth, and probable changes in the uses of property. If the owner of the land does not make use of the party wall, he does not have to pay for any part of it. Notwithstanding the fact that plaintiffs’ lot is now occupied by a dwelling house, and that so long as used as such there can be no occasion to avail of the right to half of defendants’ wall, still we are of the opinion that the wall *582may be upheld as a party wall, if it be reasonably and properly susceptible of such use. The wall seems to have been constructed in accordance with the regulations, looking to stability, safety, etc., and there is no evidence to show that it cannot be availed of as a party wall, should plaintiffs hereafter desire to make use of it as such. Under these conditions, we think it was error to direct a verdict for the plaintiffs.

3. There was no error in excluding evidence of the value of the half of the wall that was on plaintiffs’ lot. If the defendants had no right to construct the wall as a party wall, for which purpose they entered, they clearly cannot claim the benefit of sec. 1003 of the Code [31 Stat. at L. 1349, chap. 854], which is limited to those who enter into possession of the premises under a title which they “had reason to believe, and did believe, to be good,” and erect valuable and permanent improvements in good faith. Moreover, if the wall be not such as to constitute an available and legal party wall, it would be absurd to say that it nevertheless constitutes a valuable and permanent improvement. If not a party wall, it is an encumbrance or a nuisance. Smoot v. Heyl, supra.

4. We do not understand, under the circumstances, why plaintiffs should have sued for more land than is occupied by the defendants’ wall, but that is no hindrance to the recovery of a less portion than the whole sued for. Code secs. 993 and 1000. The defendants under their claim of the right to erect a party wall might well have disclaimed as to any part of the land sued for that was not occupied by the wall. Crandall v. Lynch, 20 App. D. C. 13-82.

For the reasons hereinabove given, the judgment will be reversed, with costs, and the cause remanded for another trial.

Reversed.

• A petition for a rehearing was denied.