Opinion by

We have concluded the judgment in this case must be reversed and our only doubt is whether the reversal should be with or without a venire. The husband of appellee was killed by the falling of the front wall and part of the floors of a building occupied by appellant as a slate mantel and imitation tile factory. The deceased husband was an employee of appellant and was engaged in the performance of duties for which he was employed when the building without warning collapsed and the fatal injuries resulted. Appellant occupied the building as tenant under a lease in writing designating the purpose for which it was to be used. It was used for the purpose stated and there is no evidence except that of the expert who examined the premises immediately after the accident to show that the use made of the building was an improper one, or that it was not suited to the use for which it was rented. The negligence charged is that appellant failed to provide and maintain a safe place to work, and that he negligently and carelessly permitted the walls, joists and floors to be and remain in an unsafe condition and the floors to be overweighted. No evidence was introduced to show that the joists and floors were not in good condition at the time and before the happening of the accident, or that the place was unsafe in any respect. The negligence charged in these respects must be considered out of the case so far as the record now stands. The single charge of negligence remaining is that the floors were overweighted, and this was the only question pressed at the trial. We agree with the *170contention that the overloading of the floors under the circumstances of this case might properly be left to the jury in order to determine whether the accident was due to this cause. But the overloading, if it be a fact, must be established by testimony like any other substantive fact, else there is nothing to submit to the jury. The only witness produced to sustain this allegation was an expert engineer of construction who had served as a building inspector for the city, and as such was familiar with the building in question. He went upon the premises soon after the accident, made observation of the conditions as he then saw them, and testified that in his opinion the accident was caused by overloading the floors. He did not know as a fact that the floors were overloaded, or indeed to what extent they were loaded, but judging from the broken joists and other conditions found on the premises he gave it as his opinion that overloading caused the collapse. It is a close case on the vital question whether the opinion of this expert alone, based upon what he saw after the accident, was sufficient to carry it to the jury. We have concluded, however, in view of the fact that as building inspector he was familiar with the building for several years; that prior to the occupancy by appellant, as tenant he had condemned it and required repairs to be made; that immediately after the accident he had examined every part of the collapsed building and found slate slabs estimated to weigh 175 pounds per cubic foot on some of the floors and considerable quantities of slate stored in every part of the building as well as piled on the ground among the debris; that these facts and the opinion of the expert based upon them warrant a submission to the jury on the question of overloading. But it must not be overlooked, that all of these facts might be true, and yet the direct cause of the accident be the falling of the front wall of the building by reason of defective construction. Someone seems to have been at fault, and the important question to all concerned is whether it was the owner of *171the premises or the tenant who occupied them. This depends upon what caused the collapse of the building. Was it occasioned by the tenant overloading the floors or did it result from the faulty construction and repair of the walls by the owner? Separate suits were brought, one against the owner and the other against the tenant. The plaintiff was clearly within her legal rights in thus instituting two suits on the theory that either the tenant or the owner was answerable in damages for the trespass committed, and since the liability of one or the other depended upon the facts which were in dispute, the only safe course to follow was to sue each party before the statute of limitations became a bar to either suit. While it is possible that a judgment may be recovered against the defendant in each suit, the plaintiff can only claim one satisfaction: Seither v. Traction Co., 125 Pa. 397. At this point and for these reasons it will avoid repetition to state that the seventh assignment of error is without merit.

The question to be determined is who is responsible for the injuries for which damages are claimed. Was the fault that of the owner or tenant? In such a controversy the tenant clearly has the right to introduce testimony tending to show that he was without fault and that the negligence of the owner was the cause of the accident. In this respect the learned trial judge erred in refusing to allow several offers of testimony. It was competent for appellant to show that the building had been condemned as being unsafe before its occupancy by him; that it had been improperly repaired by the owner; that the walls had not been properly bonded; that the owner had notice of these defective conditions at the time repairs were made; and that as a result of the defective construction of the walls the building collapsed. The defense was twofold, first, that the floors were not overloaded, and second, that the collapse of the building was caused by defective walls. Appellant was entitled to the full benefit of both branches of his defense; and as we *172read the record this was denied him. It was competent to show whose duty it was to post the notices, and we see no reason why the inspector who had to enforce the law might not testify as to the rule or custom in posting notices, but we do not hold this to be reversible error because the fact could be proven by offering the act of assembly in evidence. It was clearly competent for appellant to show that the repairs to the walls had not been properly made when required and that the owner had notice of the unsafe alterations he proposed to make, and that these conditions remained to the time of the accident. Items of testimony tending to show these facts should have been admitted.

Also, it was competent for appellant to show that at the time of the accident the floors were only loaded in the usual way and that there was no unusual loading on that day to cause the accident. For these reasons we think the third, fourth, fifth and sixth assignments of error must be sustained, as also must the tenth but for a different reason. The first, seventh, eighth and ninth assignments are overruled.

We do not find in the record any evidence to warrant the instruction complained of in the tenth assignment. There is no evidence to show how much weight was on any floor, nor that it was the duty of the tenant to make an inspection for the purpose of ascertaining the carrying capacity of the floors and walls in his business. The difficulty with this case is, and it applies to both sides, there is too much theory and not enough facts. This case is not necessarily ruled by McKenna v. Paper Co., 176 Pa. 306; but when it is again tried substantive facts should be proved as a foundation upon which to base the assumptions, theories and distinctions relied on to sustain or defeat a recovery.

Judgment reversed and a venire facias de novo awarded.