Ladd, J.
*5991 2 *598The liability of the defendants, as sureties on the contractor’s bond, for the amount paid to satisfy the mechanics’ liens in excess of the contract price, is conceded, unless avoided by some change in the contract. Owing to the situation of the surety, he must be treated with the utmost *599good faith, and may insist on the strict terms of his obligation. School Dist. v. Reichard, 50 Iowa, 98; Starr v. Blatner, 76 Iowa, 358; Brigham v. Wentworth, 11 Cush. 123; Plow Co. v. Walmsley, 110 Ind. 242 (11 N. E. Rep. 232); Erickson v. Brandt, 53 Minn. 10 (55 N.W.Rep. 62); Bragg v. Shain, 49 Cal. 131; Mayhew v. Boyd, 5 Md. 102; Miller v. Stewart, 9 Wheat. 680. If a material alteration is made in the contract without the surety’s consent, he is discharged, even though the alteration may be for his benefit. Brandt Suretyship, section 338. We inquire, then, whether the contract between plaintiff and Monroe was altered or any of its conditions waived by the parties. In establishing the mechanic’s lien the court found that the contractor had done extra work, valued at five hundred and seventy-four dollars. This was without special bargain evidenced in writing, as required by the contract, a portion of which we set out: “Extra work: In case it is deemed necessary during the construction of the building to have more or extra work done than is specified or shown in the plans, such work is to be done by the contractor, but he is required not to proceed to make such work without a special bargain or contract for the same, and minuted on the back of the original contract; otherwise it is not binding upon either of the parties.” The evident object of this clause was to prevent changes or alterations on mere suggestion, without fixing their extent, and to avoid controversy and litigation as to what were extras and their value. But the extra work was done at the request of the plaintiff, and upon her oral promise to pay, without special bargain or agreement minuted on the original contract, as therein required. To our inquiry it is quite immaterial whether the phrties might waive this condition, and substitute the method pursued. But see Smith v. Gugerty, 4 Barb. 614; Bartlett v. Stanchfield, 148 Mass. 394 (19 N. E. Rep. 549); Osborne & Co. v. Backer, 81 Iowa, 379; Viele v. Insurance Co., 26 Iowa, 53; King v. Insurance Co., 72 Iowa, 315.
*600By the terms of tbe original contract, each party was relieved from liability unless the extra work was done in pursuance of a special bargain in writing. It was not on tbe original contract that plaintiff was beld for tbe extra work in tbe action referred to, but because of tbe separate oral agreement made witb Monroe, substituted therefor. Tbe obligations of tbe sureties was that tbe contractor “comply with all tbe conditions of said contract, and faithfully perform all tbe undertakings therein stipulated by him to be performed.” Monroe was not bound to do tbe extra work save on tbe conditions stipulated, and, if plaintiff suffered loss by reason of tbe adoption of another method, tbe sureties are under no obligation to recoup it. Nor does tbis change affect other portions of tbe contract, as it expressly provides for such a contingency. Tbis alteration was such as tbe parties were permitted to make, on tbe condition that liability should not attach.
3 II. Tbe contract provided that Monroe “furnish all materials such as are called for in tbe plans, detail drawings, and specifications,” and that be use “such materials as hereinafter described.” There is also a provision that “bo will be further beld to submit, as to tbe character of tbe materials to be used and work done, to tbe judgment of tbe superintendent, and to secure from him all necessary interpretations of tbe designs and plans, and all necessary certificates regarding bis payments on tbe contract; also for all additions to, or deductions from, tbe same, which may result from extra work or changes of designs or plans.” Tbe owner was permitted to change tbe plans or designs, and, in so far as necessary to meet such change, material differing from that specified might be required. Tbis much must necessarily be inferred from tbe right to make such alterations. Further than tbis, and in no other way, tbe right to require material of a quality or character other than described in tbe specifications is not reserved to tbe owner. True, tbe character of tbe materials was to be submitted to tbe judgment of tbe superintendent, but only for bis determination whether these *601were as required by the contract. This condition does not allow the superintendent to reject material furnished in strict accordance with the specifications, and arbitrarily substitute that of different quality or construction to suit his whim or fancy. No one could safely contract for the erection of a building, and give another such an option. And the contractor was to furnish the materials, and not the owner, at his expense. But the evidence in this‘case clearly shows that the plaintiff virtually took the erection of the building from the control of the contractor. She directed the workmen, rejected material which conformed to the specifications, and bought other, without consulting Monroe. Lumber bought, after advertisement, of the lowest bidder, was rejected, and that of a different quality, at an increased price, procured of another firm. The hardware was changed, at an additional expense of eighty-three dollars. The millwork, after delivery, was refused, and ordered of another. Indeed, the contractor was not permitted to choose from whom he would purchase materials. Doubtless the plaintiff has a better house because of these changes, but by ignoring and altering the conditions of her contract the sureties were relieved from liability. They contracted for compliance with the terms of the contract, that Monroe furnish materials, and that these be of the character fixed by the specifications. The importance of the alterations is apparent. The contractor was deprived of the advantage of competition in purchasing, and obliged to pay much more than he would for that specified. It is no answer to say Monroe acquiesced in all this. The parties had the right to waive conditions, but in doing so disregarded those on which the indemnity rested. The extent of these alterations we need not determine. They were material, and there the inquiry must end. Bethune v. Dozier, 10 Ga. 235; Simonson v. Grant, 36 Minn. 439 (31 N. W. Rep. 861); Paine v. Jones, 76 N. Y. 274; Brennan v. Clark, 29 Neb. 385 (45 N. W. Rep. 472); 24 Am. & Eng. Enc. Law, 837.
*6024 *601III. The plaintiff urged that by signing orders for the payment of certain work, including extras, the defendants *602have waived objections to alterations in tbe contract. But it is not shown that they had any knowledge of the omission to comply with its terms. There can be no waiver without knowledge of the facts upon which it is based. But, aside from this reason, such an issue was not tendered in the pleadings, and therefore cannot be considered. The decree of the district court is aeeirmed.