The main causes of building defects Building surveyors across all sectors are routinely tasked with investigating building defects to commercial and residential portfolio's. By understanding how some of these errors can occur, the surveyor can be mindful not to repeat such practices. TK Surveying Group have compiled a range of common reasons as to why defects may arise. Not in any particular order. 1. Water Although under-rated as the primary agent of decay and deterioration.