Opinion by

This is an action of assumpsit brought to recover the difference between the cost of covering the main roof of the defendant's bank building with a slag and a copper roof.

At the request of the defendant’s architect, the plaintiffs tendered a bid or proposal for the erection of a bank building for the First National Bank of Wilkes-Barre, Pennsylvania. The proposal was in writing and contained several paragraphs, each making a different and conditional *651bid for the work to be done and the materials to be furnished. By paragraph four, the plaintiffs offered to construct the building for $112,983. In paragraph six, the plaintiffs bid $663 on the clock frame, and stated that they included cornice of granite in place of concrete for alley in No. 4 estimate. This paragraph concluded with the words: “Main roof estimate slag.” A few days after the bid, the secretary of the building committee of the defendant bank advised the plaintiffs that the committee had accepted their bid “as set forth in paragraphs four and six of same.” The parties entered into a contract for the construction of the building in pursuance of the bid and its acceptance, by the ninth article of which the owner was to pay the contractor $112,983, “as stipulated in proposition or paragraph four and $663 as stipulated in proposition or paragraph six of the bid of contractors a copy of which is hereto attached.”

Among the specifications was the following: “The roofs (excepting the front portion and main roof which is copper), shall be covered with a five-ply slag covering of the Warren-Ehret, or Owen D. Jones, manufacture.” The contract provided for three roofs on the building of different altitudes, the front roof, the main roof, and a third roof over the directors’ room. During the construction of the building a dispute arose between the contractor and the owner in regard to the covering for the main roof. The contractor claimed that the main roof was to be covered with slag; the owner, that it was to be covered with copper. It was agreed that the contractor should furnish a copper covering and that the dispute should be adjusted by an action of law. This suit was brought to recover the difference between the cost of the slag and copper covering of the main roof. The learned court below instructed the jury to find a verdict for the plaintiffs and the defendant has taken this appeal.

The defendant bank contends that the contract required the plaintiffs to erect the building according to the plans and specifications of the architect, and that the specifica*652tion above quoted required the main roof to be covered with copper. Its contention is that the front and main roofs were to be covered with copper and only the roof over the directors’ room was to be covered with slag. It is further claimed by the defendant that the words, “main roof estimate slag,” added to paragraph six of the plaintiffs’ bid are without effect and do not change the specification providing for the roofing.

We do not agree with the defendant’s contention. The specification in question was ambiguous and was so regarded by bidders and architects, even by Mr. Kipp, defendant’s architect, who prepared the plans and specifications for the building. Mr. Shepherd, observing the ambiguity in the specification, attempted to communicate with the architect before he submitted the plaintiffs’ bid but was unable to do so by reason of Mr. Kipp’s illness. He then submitted to the architect through the latter’s wife certain questions as to the proper construction of the specification but received no definite answer, the architect replying “you better figure on copper roof.” This occurred on the morning the bids were to be submitted, and Shepherd testifies that he could not estimate the cost of a copper covering without a specification, and the time was too short for him to get a bid on a copper roof basis. Another bidder communicated with the architect on the subject in the same way. The first reply he received was that the main roof was to be of slag, but on his suggestion that the roof was too steep for slag, the architect replied again through his wife: “You better figure copper.” Another architect was called and he testified that there was nothing on the drawings to show the character of the roof, and that as there were three roofs he would interpret the specifications to cover the portion over the main bank room with slag.

The specification being ambiguous and open to different interpretations, it was proper for the plaintiffs in submitting a bid to specify the character of covering of the main roof on which they made their estimate. This relieved *653the bid of any uncertainty and distinctly notified the defendant and its architect of the construction placed upon the specification by the plaintiffs. This bid, as will be observed, was accepted by the building committee. The resolution adopted by the committee and communicated to the plaintiffs, accepted the bid as set forth in paragraphs four and six, the latter of which contains the notice to the owner that the plaintiffs made their bid on the basis of a slag covering for the main roof. The contract provides that the owner should pay the sums stipulated in the two paragraphs and copies of those paragraphs were attached to the contract. The bid was, therefore, made and accepted upon the distinct notice by the contractor to the owner that it was upon the basis of a slag covering for the main roof. The proposal distinctly notifies the owner that the roof is to be slag, the building committee accepts the proposal including this notice, and the contract specifically provides that the sums named in the two paragraphs, one of which contains this notice, will be paid by the owner to the contractor for the construction of the building. This is a construction of the specification providing for the material for the roofing by both parties, and neither is at liberty to reject it now. When the building committee accepted the proposal, including the plaintiffs’ construction of the specification, and subsequently wrote it into the contract, both parties were bound by it, irrespective of the true interpretation of the specification. If the defendant intended the main roof to have a copper covering, it should have at once rejected that part of the proposal which disclosed the fact that the plaintiffs’ bid was made on a basis of a slag covering. The bank not only did not reject this part of the proposal, but in terms accepted the sixth paragraph of the proposal which included the slag estimate. The sixth paragraph in its entirety became a part of the contract for the construction of the building. The bid of $112;983 was on the basis of a slag covering for the main roof, and it is manifest that if it had been made on the basis of a copper covering for *654the roof it would have been increased by the difference between the cost of a slag and a copper covering. It was, therefore, the duty of the defendant bank when it received the proposal notifying it that the contractor had made his estimate on a slag roof to reject that part of the proposal and give notice that the roof was to have a copper covering. In the absence of such action by the bank, it cannot now assert that the bid for the work was made on the basis of a copper covering for the main roof.

The learned court below was right in directing a verdict for the plaintiffs, and the judgment entered thereon is affirmed.