If you are the homeowner doing work on the property that is your homestead, you do not have to hire a contractor for electrical, mechanical, or plumbing work. However, you are required to get a permit, and the work must be able to pass inspection.
Additional resources
When do I need an engineer?
A variety of project types require the services of an engineer. For example, remodeling a building to remove structural columns or constructing a retaining wall that is four feet taller. This handout from the Texas Board of Professional Engineers is a good starting point to determine whether you need an engineer. You can also call our Permits office at 817-297-2201 ext. 3000. (Please see document below)
The Texas Board of Architectural Examiners once provided a handout to help you determine if your project requires an architect. Please note that instead of updating the handout, they now provide an interactive questionnaire to help you determine if you need an architect, which you can access here.