Why does a screw loosen as opposed to tightening over time? Why does not the torque tighten up the screw?

http://imfl.sci.pfu.edu.ru/forum/index.php?action=profile;area=summary;u=713194

<h2>Residential Steel Roof Covering Product Evaluation</h2> Or else, the subjected metal locations are still at risk to condensation in addition to undesirable heat transfer. The more you take a price quote apart