Solar insolation models have been extensively reviewed for Quetta, Pakistan. The correlations a/ suggestÿ by Klein are found suitable for global solar radiations at Quetta and that Quetta on an average receives 763 Jo|les/nf/sec. Estimation of monthly daily diffuse radiation although found quite reliable needs further investigations. We found reliable estimates for both global solar and diffused solar radiations using sunshine hours. The 60 tilt surface of flat plate collector facing south receives about 1.7 to 2.0 times the maximum irradiation on a surface with a tilt equal to latitude at Quetta, especially in summer, whereas maximum solar energy round the year is received for the same tilt angle. The other tilt angles of a flat plate collector are also found suitable to intercept both global and in particular, maximum diffuse solar radiations provided declination angles and solar trackings are adjusted. For thermal performance of building designs, the use of transparent insulation (Tl) at Quetta particularly in a LEGIS south facade is recommended. Qur analysis on the use of a two-axis tracking flat plate collector is found in agreement with estimates of solar radiations. We suggested architectural design of buildings and residences at Quetta from view point of using both active and passive solar heating/cooling systems and with environmental and climatic considerations. We recommend installations of prototype solar heating and cooling systems for experimental Verification of our estimated values of solar radiations and that the monitoring of their operational modes is as essential as architectural designing of buildings itself. Duirnel variations of solar radiations have a significant affect as heat transfer and thermal performance of building designs.