On one hand Pakistan is facing severe energy crises, and on the other the planet earth is going through global warming. The only solution for both is low carbon planning. The purpose of this book is to show the benefit of low energy residential designs. This book has taken into account analysis of three case studies of Eco-Houses selected on the bases of fenestration insulation; designed with considerations of energy efficiency and traditional principals; which has been examined in regard with economy, material, and techniques. The two prong strategy was devised for both the houses, separately. A comparative analysis of the radiation penetration through fenestrations for the two houses was conducted on two typical days. One is the longest day of the year i.e. 22nd of June and the other is the shortest day of the year i.e. 22nd of December. The results obtained provide us the substance to statistically show the benefits of low energy designs. Moreover, the findings highlight an importance by providing an insight for the architects to pay attention towards as well as adopt the measures for designing low energy buildings.