More disputes arise and more adversarial positions are staked out because of actual or perceived changes in a construction project than for any other reason. Aggressive contractors will threaten slow-downs and work stoppages if they don't get paid. Overbearing owners will insist that unknown conditions, extra features, and an expanded project are covered by the original bid price.

A seemingly minor in-the-field alteration of a lateral support may, weeks or months later, change the route of a surface drain to a more expensive and even dangerous location. Many shop drawings, materials specifications, detailed plans and installation requirements are not known when the work is bid. New instructions arise instantly in the field through the superintendent or architect or owner's representative. One side may have no recourse except to make the change or get thrown off the job and lose the ensuing legal fight, or the contractor will have a valid claim for extras and the owner will bear the consequences. Informal change requests may be backed up by the full force of law; in other circumstances the impact of changes will be ignored by the courts, and claims for extra payment will not be enforced.

Most construction contracts specify the steps required before additional work or deduction in work is authorized. Construction contracts typically provide that a change in dollars or time must be described and submitted in writing, must be submitted so many days in advance of the work (or so many days after the owner's request), signed by designated people, and reviewed and approved within so many days of submittal.

But most contracts fail to anticipate other issues. Care must be taken that any affected third party also signs off on a change order (a construction lender, a surety or bonding company, a landlord for improvements to property under a long term lease). A change in scope of work between subcontractors should be signed off by the prime contractor. See Superior Gunite v. Ralph Mitzel, Inc. (2004) 117 Cal.App.4^th 301.

If the change implicates health or safety concerns or building code requirements, permits may need to be applied for and obtained before work on the change begins. See California Pools, Inc. v. Pazargad (1982) 131 Cal.App.3d 601. An extreme example of the interplay of building laws and contract rights is Heple v. Kluge (1952) 114 Cal.App.2d 473. The contractor bid a job on plans that did not comply with building requirements. The courts ruled the contractor could completely ignore those building plans and instead be paid much more than the contract price.