I call them Constraints. You may know them by another name. Obstacles. Restrictions. Hurdles. Red Tape. No matter the project, there are always constraints. There is nothing sexy or exciting about constraints, but you ignore them at your peril. Clients expect you to know about such things. In almost every case, you will have to surrender to constraint's influence eventually, often at great cost for re-working your design to comply.
As the world gets more sophisticated and complicated, the list of potential constraints grows. Building code and zoning used to be about the extent of the constraints you might face. Now the list is at least 15 topics. Besides Building code and zoning, we have added storm water management, hazardous materials, department of transportation, ADA (which now applies to everything), special inspections, and a number of issues that are client-driven but not always obvious. Our Constraints Checklist is downloadable here.
To address the growing list of client-specific Constraints, we have also developed a questionnaire template to try and elicit this information before it gets to be a headache. Here is the Questionnaire for download too.