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GREEN BUILDING TIP: Pick Windows That Don't Waste

Windows with internal grilles are more energy efficient than divided-light windows

Posted on Jan 13 2010 by Daniel Morrison

True divided-lightTrue divided light sash have small panes of glass separated by muntins. Because large pieces of glass used to be difficult (or expensive) to make, older houses have windows with two, four, or six small lights per sash. These multiple-light sash are also called "divided-light sash" or sometimes "divided-light windows." windows lose more heat.
Heat loss is highest at the edges of window glass. True divided-light windows lose more energy than windows with internal muntins because there are many more edges where heat can escape. Simulated divided-light windows, with the muntins sandwiched between sheets of glass, retain more of the thermal performance of the larger glass size than true divided-light windows. Because National Fenestration Rating Council ratings are not based on divided-light windows, they may overstate the thermal performance of divided-light windows.

This GREEN BUILDING TIP is from our Strategy Generator. Build a tip sheet for your green building or remodeling project under the Strategies & Details tab.


GREEN POINTS

LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. : Up to 3 points for high-efficiency windows.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. /ICC 700: Depending on the climate zone up to 12 points for windows that meet U-value and Solar Heat Gain Coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. maximums.

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1.
Mon, 01/18/2010 - 16:35

please define terms
by Mark Bartosik

Helpful? 1

Consumers reading this are unlikely to know what a "divided-light window" is.
Please define the terms internal muntin, and divided-light.
thanks


2.
Mon, 01/18/2010 - 17:15

Definitions
by Martin Holladay, GBA Advisor

Helpful? 0

Mark,
A muntin is a strip of wood or metal separating and holding panes of glass in a window sash. Each pane of glass (or each "insulated glazing unit") separated by a muntin is called a light.

Most modern windows have one light per sash. Because large pieces of glass used to be difficult (or expensive) to make, older sash often had two, four, or six small lights per sash. These multiple-light sash were said to be "divided-light sash" or sometimes "divided-light windows."

True divided light sash have small panes of glass separated by muntins. Simulated divided-light sash have one large piece of glass with applied grilles that look from a distance like muntins — to give modern windows that "old-timey" look. In some cases, these grilles are placed between two sealed pieces of glass -- these are the "internal muntins" mentioned above.


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