https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/09_afh_ch8.pdf

When there is no published TPA for an airport is when the FAA’s recommendations on pattern altitudes should be followed. According to the AC, light aircraft should use 1,000 feet AGL, heavy and turbine‐powered aircraft should fly the pattern at 500 feet above the established traffic pattern altitude, and ultralights should operate no higher than 500 feet below the powered aircraft TPA.