This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
If the written contract contains an express provision that no change or modification thereof can be made, except by writing to be signed by one or both parties, the parties to such contract may, nevertheless, modify or abrogate it by subsequent oral agreement, since the oral agreement will operate as a waiver of the terms of the contract inconsistent therewith, including that term which requires subsequent modification to be in writing.1 Questions of this sort are often presented in building contracts, where it is provided that modifications or contracts for extra work must be in writing, and subsequent oral agreements for extra work or modifications are held valid.2 Unless waived, however, such a provision prevents recovery for extra work.3 A provision that no extra work shall be done without a written order from the architect and an express agreement as to the extra cost has no application to extra work ordered by the owner under a provision of the contract allowing him so to do.4 So a provision in a building contract that work cannot be sub-let without the written consent of the owner first had, may be waived by a subsequent oral agreement.5 A provision in a sub-contract for constructing a railroad that stone could be substituted for that specified only on the written consent of the engineer of the contractor may be waived by subsequent oral contract.6 The party for whose benefit such provision is inserted may modify or waive it.7 If the architect is authorized to modify the plans by a written order, he has no authority to order modifications orally.8 A provision that the architect has authority to modify plans only by written order has been held to be for the benefit of the owner alone, and hence subject to modification by him, without the consent of the contractor.9 In a recent case10 such provision has been held to be for the benefit of both owner and contractor, and to be modified only with the consent of both. So a provision in an insurance policy that certain provisions thereof could be modified only by writing indorsed on the policy may be modified by a subsequent oral contract.11 The original view entertained by the courts was that such written provisions in insurance policies could not be waived by subsequent oral contracts.12
1 Fire Ins. Association v. Wick-ham, 141 U. S. 564; Insurance Co. v. Wilkinson, 13 Wall. (U. S.) 222; Foster v. McKeown, 192 111. 339; 61 N. E. 514; Copeland v. Hew-ett, 96 Me. 525; 53 Atl. 36; Pech-ner v. Ins. Co., 65 N. Y. 195.
2 Davis v. Badders, 95 Ala. 348; 10 So. 422; Chicago, etc., Ry. v. Moran, 187 111. 316; 58 N. E. 335; Michaud v. MacGregor, 61 Minn. 198; 63 N. W. 479; MeLeod v. Genius, 31 Neb. 1; 47 N. W. 473; Crowley v. Guaranty Co., 29 Wash. 268; 69 Pac. 784.
3 Heard v. Dooly County. 101 Ga. 619; 28 S. E. 986; Wortman v. Kleinschmidt, 12 Mont. 316; 30 Pac. 280; Coorsen v. Ziehl, 103 Wis. 381; 79 N. W. 562.
4 Cooper v. Hawley, 60 N. J. L. 560; 38 Atl. 964.
5 Gannon v. Shepard, 156 Mass. 355; 31 N. E. 296; Bartlett v. Stanchfield, 148 Mass. 394; 2 L. R. A. 625; 19 N. E. 549.
6 Chicago, etc., Ry. v. Moran, 187 111. 316; 58 N. E. 335.