Other considerations

Insulation

Thermal insulation or superinsulation (type, placement and amount) assists in significantly reducing unwanted heat transfer.

Special glazing systems and window coverings

The effectiveness of direct solar gain systems is significantly enhanced by insulative (e.g. double glazing), spectrally-selective glazing (low-e), or movable window insulation (window quilts, bifold interior insulation shutters, shades, etc.).

Generally, Equator-facing windows should not employ glazing coatings that inhibit solar gain.

There is extensive use of super-insulated windows in the German Passive House standard. Selection of different spectrally-selective window coating depends on the ratio of heating versus cooling degree days for the design location.

Glazing selection

Equator-facing glass

The requirement for vertical equator-facing glass is different than for the other three sides of a building. Reflective window coatings and multiple panes of glass can reduce useful solar gain. However, direct-gain systems are more dependent on double or triple glazing to reduce heat loss. Indirect-gain and isolated-gain configurations may still be able to function effectively with only single-pane glazing. Nevertheless, the optimal cost-effective solution is both location and system dependent.

Roof-angle glass / Skylights

Sloping roof-angled glass is difficult to shade and insulate without sophisticated movable systems. In hot climates with significant degree day cooling requirements, it can create a summer solar furnace (from the Ancient Greek / Roman term "heliocaminus").

Roof-angled glass or skylights are not optimally placed to receive low-angled winter sun. At the same time, they are the site of heat loss during winter from the buoyant warm air that rises. As a result, they will increase heating and cooling energy requirements, which exceeds the benefit of daylight energy consumption reduction compared to more energy-efficient lighting systems such as light tubes.

Transparent glass and plastic have little structural strength. Vertically, they bear their own weight because only the thickness is subject to gravity. As the angle tilts from vertical, an increased area (the sloped cross-section) must resist gravity. Glass is brittle - It does not flex much before breaking - To counteract this, you must increase thickness, or structural supports - Both increase overall cost, and reduce solar gain potential. Sloped glazing is exposed to the weather, leaks, hail, ice-and-snow load, wind, and material failure. Excess solar gain, harsh lighting, and undesirable heat transfer thru sloped glass are difficult to control. “Therefore, vertical glazing is the overall best option for sunspaces.”