when did cavity wall insulation become part of building regulations
Cavity wall The typical cavity wall method of construction was introduced in Northwest Europe during the 19th century and gained widespread use from the 1920s. In some early examples stones were used to tie the two leaves of the cavity wall together,[3] while in the 20th century metal ties came into use. Initially cavity widths were extremely narrow and were primarily implemented to prevent the passage of moisture into the interior of the building. The widespread introduction of insulation into the cavity began in the 1970s with it becoming compulsory in building regulations during the 1990s.[clarification needed]
Great Wall of China The Great Wall of China is a series of fortifications made of stone, brick, tamped earth, wood, and other materials, generally built along an east-to-west line across the historical northern borders of China to protect the Chinese states and empires against the raids and invasions of the various nomadic groups of the Eurasian Steppe with an eye to expansion. Several walls were being built as early as the 7th century BC;[2] these, later joined together and made bigger and stronger, are collectively referred to as the Great Wall.[3] Especially famous is the wall built in 220–206 BC by Qin Shi Huang, the first Emperor of China. Little of that wall remains. The Great Wall has been rebuilt, maintained, and enhanced over various dynasties; the majority of the existing wall is from the Ming Dynasty (1368–1644).