37 Tex. Admin. Code § 259.427
One or more secure exercise areas shall be provided. Where outdoor exercise areas are provided, alternate areas shall be provided for exercise during inclement weather. Outdoor exercise areas should be covered with a security enclosure. Where outdoor exercise areas are not provided, facility design shall provide for access to sunlight. A toilet and drinking fountain shall be readily available. Exercise areas for facilities of less than 100 inmates based on design capacity shall not be less than 800 square feet. Exercise areas for larger facilities shall provide 15 square feet per inmate for the maximum number of inmates expected to use the space at 1 time, but not less than 1000 square feet for each exercise area. Each direct supervision housing area shall have an exercise area within close proximity which should be adjacent to the housing area.
37 Tex. Admin. Code § 259.427