Do I need a permit for pergola or trellis in Dallas County (Unincorporated)?

It depends. Whether pergola or trellis needs a permit in Dallas County (Unincorporated) comes down to the details of your project.

The 2012 International Residential Code adopted by Texas Local Government Code 214.212 does not name pergolas or arbors on its list of work exempt from a permit, and the only roof-type item on that list is a small window awning, so each city decides how it treats an open pergola. Attached or roofed designs get the closest look. Texas Local Government Code 214.221 bars a city from applying its municipal building code to the construction of a solar pergola. The wiring for the solar system is still electrical work that requires a licensed electrician under Occupations Code Chapter 1305. Section R105.2 states that an exemption from a permit does not authorize work that violates the code or other local laws or ordinances, so setbacks still apply. A solid, waterproof or louvered roof turns an open pergola into a roofed structure, which departments generally review like a patio cover, with attention to roof framing and wind loads. An open lattice or rafter pergola is the version most often treated as minor, so if you are comparing designs, ask your department how it treats each one before you buy a kit.