Prior to the 1970 ’ s, many buildings in the United States and in a number of other lands were less insulated and airtight than later designs.
१९७० च्या आधी अमेरिकेत व इतर अनेक देशांत, बहुतेक इमारती हवा खेळती राहील अशा रितीने बांधलेल्या होत्या.