14. A wall cavity with a reflective surface has a higher R -value than just the cavity Explain why this occurs. __

wall cavity with a reflective surface has a higher R-value than a simple cavity because the reflective surface reduces heat transfer via radiation. Here's a breakdown:<br /><br />* **R-value:** Measures a material's resistance to heat flow. Higher R-value means better insulation.<br /><br />* **Heat Transfer Methods:** Heat transfers in three ways: conduction, convection, and radiation.<br /><br />* **Cavities and Convection:** A simple air cavity reduces heat transfer primarily by limiting conduction. Air is a poor conductor. However, convection currents can still form within the cavity, where warmer air rises and cooler air falls, carrying some heat across the space.<br /><br />* **Reflective Surfaces and Radiation:** A reflective surface within the cavity minimizes radiant heat transfer. Instead of absorbing heat and then re-radiating it, the reflective surface bounces the radiant heat back towards its source. This significantly reduces the amount of heat that crosses the cavity.<br /><br />Therefore, by addressing radiation in addition to conduction and minimizing convection, the reflective cavity achieves a higher overall resistance to heat flow and thus a higher R-value.<br />