Window Rating Terminology

Windows are rated by the National Fenestration Rating Council.  The rating takes into account the following five criteria:

• U Factor - A measure of the resistance to heat transfer on a scale of 0 to 1.2.  The lower the number, the greater the resistance. To qualify for tax credits the window must have a rating of 0.30 or less.
• SHGC - Stands for Solar Heat Gain Coefficient.   This rating measures how well a window blocks solar heat gain on a scale of 0 to 1.0.  The lower the number the more efficient at blocking the suns heat from a home’s interior the window is.  A rating of 0.80 means 80% of the solar energy hitting the window gets through. To qualify for tax credits the window must have a rating of 0.30 or less.
• Visible Light Transmittance - A measure of the amount of sunlight that can pass through a window on a scale of 0 to 1. The higher the number the more light will reach the interior of your home.  Tinted windows have relatively low visible light transmittance.
• Air Leakage - A measure of a windows air infiltration in cubic feet per minute per inch of crack or seam.
• Condensation Resistance - A measure of the windows ability to resist the formation of condensation on its interior surface. This is very important in evaluating the durability of a window relative to others.  It is rated on a scale of 0-100, with a higher number indicating a better resistance to condensation.

These ratings are listed on a sticker located on the windows themselves or often available in manufacturers literature or on their websites.

For more information: www.nfrs.org

www.efficientwindows.org

Call Sacramento Building Performance at 916-416-0676, or email us at info@sacsustainable.com, to schedule a free consultation to discuss the benefits or to schedule your Home Performance Assessment.