An in situ experimental procedure suitable for the development and validation of slat-type blind models used in building cooling load calculations is presented. Unique requirements of the experimental facility are presented, and measured data from the facility are compared with existing experimentally validated models. The experimental uncertainty associated with the measured solar transmittance is shown to be less than +/- 0.05, well within the range of accuracy required for the development of cooling load calculation procedures. The new procedure was used to validate the fenestration model in Energy-Plus, a heat balance based cooling load and energy calculation program.