This paper presents the energy and economic analysis used to determine cost effective requirementslevels to the thermal standard for buildings in Lebanon. The heating and cooling energy use fordifferent buildings types (18 buildings) according to the variation of envelop parameters was simulatedfor realistic cooling and heating schedules and five Lebanese climatic zones. Parameters investigatedincluded, construction type, insulation levels, window sizes and solar protection. The energysimulation program VISUAL-DOE.3 was used for the energy use simulations. A total of 680 modelruns were conducted.Cost-effective insulation and envelop parameters options for the building-owners and builders weredetermined and suggested as economical acceptable solutions to improve the energy performance ofbuildings in Lebanon.The results show that the cost-effective measures may reduce: thermal cooling energy and coolingneeds by + 23 to 33% and the heating energy by +18 to 40% according to building type and climaticzone. The pay back time of proposed requirements will be from 2 to 9 years for residential buildingsand from 3.2 to 8.3 years for commercial buildings according to the climatic zoneTherefore, the total quantity of CO2 emissions avoided on a 20 years horizon is 1 million tonsapproximately.