Every location is going to be different, and only by discussing your house conversion project with our planning and zoning staff can you be sure to identify difficult issues before you get too far down the line. That being said, here is some info that might help you get started:
Only a house located in a zone that allows commercial use can be converted to include any non residential use. Businesses in residential zones are limited to those that can be run as a Home Occupation. View more information on Home Occupations and their limits.
A house that is in a zone with a d "overlay" (e.g. EXd) may need to go through a design review process if changes are made to the exterior of the building.
In some zones, the zoning code requires off street parking, for the commercial use. And that may be difficult to provide. Even where there is no parking requirement, it may not be practical to use an existing garage and/or driveway for parking, or to create additional onsite parking. You may find that you either need to go through a land use adjustment process, because you can't meet all of the requirements, or that you end up "curbing off" the existing driveway so it can't be used for parking. View more information on the adjustment process.
Another zoning code requirement for most house conversions is that of a six foot wide (minimum) paved pedestrian walkway between the building entrance and the street. A walkway may also be required to connect other features on the site, such as additional entrances, bike parking, etc.
We strongly suggest that you contact a planner to discuss the requirements and options for the house you are considering. You may call the zoning info line at (503) 823-7526 or visit the Development Services Center to meet with someone in person.