Building Envelope

The building envelope is everything that separates the interior of the building from its environment: windows, walls, foundation, basement slab, ceiling, roof and insulation. All the components of the building envelope need to work together to keep a building warm in the winter and cool in the summer.

Windows
Low-E insulated glass and ceramic-fritted, louvered glass walls reflect heat away from the curtain wall in the summer months and reflect radiant heat indoors in the winter months.

How Heat Travels
Heat naturally flows from warmer objects to cooler objects via the processes of radiation, convection, and conduction.

The movement of a fluid such as air is called convection. Convection is the driving cause of air leakage through seams, cracks, and other openings in your building envelope. Typically warmer air flows upward through your attic or chimney, pulling cooler air in from the basement and in through gaps around windows and doors. Sealing air leakages also helps prevent moisture infiltration, inadequate ventilation, and makes living spaces draft-free.

Conduction is the transfer of heat through a solid object, from its warmer side to its cooler side. Glass objects (such as windows) and metal are good conductors of heat and bad insulators, whereas foam and fiberglass make poor conductors and thus good insulators. R-value is a measure of a material’s resistance to heat transfer by conduction—the higher the R-value, the better its insulating properties.

Radiation of heat from objects takes the form of electromagnetic waves that travel through space. You may be familiar with radiant energy from the sun and its effect on your building envelope. A dark roof on a hot sunny day will absorb 70–90 percent of the sun’s energy and re-radiate this into your home, while SGH's white roof reflects this energy.

(Source: http://www.rmi.org/images/other/Energy/E04-11_HEB1Building.pdf)