Calculation of economical thermal insulation thickness of building envelope in Nanjing

Considers that the calculation of the economical thickness should take both  winter heating and summer cooling in hot summer and cold winter zone into account, and not directly apply a recommended or empirical value. In the light of Nanjing local characteristics, obtains a simple formula for calculating economical thickness, and uses it to calculate and analyse the thermal insulation thickness of exterior walls and roof of typical energy efficient residential building in Nanjing area.