

Low-E (emissivity) coatings, inert gas fill between the panes, and thermally-improved spacers all contribute to improved performance.
Double pane windows r value code#
In recent years, double-pane windows have improved significantly - routinely achieving a heat loss rate of U-0.30, which is the building code in some cold climates. Super-insulated windows can reach U-0.10 or about R10. An R4 window has a heat loss rate of about U-0.25. For example a window with an R-value of 3 will have a U-value of. R-value is the mathematical reciprocal (or “opposite”) of U-value. In the window world, the energy performance is expressed as the heat loss rate (U-value) and not the insulating or resistance to heat transfer value (R-value). Thoughtful design that prioritizes window placement and sizing can help get the benefits of both worlds. So trimming window area becomes a balancing act between the energy efficiency gains from reducing window area and the many additional benefits windows provide.

Windows also provide natural ventilation and emergency egress from bedrooms. And, there is a limit to how far one can take the window elimination approach.

Reducing the window area of a home is an excellent way to reduce heat loss and save money, but it isn’t a big hit with building designers who emphasize natural light, outdoor views, passive solar heat gain, and the architectural aesthetics of windows. How can these holes in zero energy envelopes be closed cost effectively? Reducing Window Area While Improving Lighting, Ventilation, and Views The performance gap becomes ridiculously wide in zero energy homes, where great attention is paid to building insulation, and the wall can be anywhere from R25 to as high as R60. The typical new double-pane window has an insulating value between R2.5 and R3. Wall insulation is required to be no less than R19 by most building codes. They are responsible for up to 48% of the heat loss from a typical home, but comprise only 7% of the envelope area. The first time you look at an energy modeling report, one thing jumps out: Windows are big holes in the energy envelope. Zero Energy Homes of the Future are Available Today.
Double pane windows r value free#
