37 Tex. Admin. Code § 260.128
One or more exercise areas shall be provided. Where outdoor exercise areas are provided, alternate areas shall be provided for exercise during inclement weather. A toilet and drinking fountain shall be readily available. Exercise areas for facilities of less than 100 offenders based on design capacity shall not be less than 800 square feet. Exercise areas for larger facilities shall provide 15 square feet per offender for the maximum number of offenders expected to use the space at one time, but not less than 1,000 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. Consideration shall be given to the requirement for offenders to be allowed access to sunlight for one hour per week after ten days confinement.
37 Tex. Admin. Code § 260.128