Mullion Windows

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Mullion Window
Mullion Window
Other Names:
Replacement Mullion Window, Mullion Casement Windows
Windows which include a vertical divider or bar in the frame between the windows or between the sashes of a window.

Replacement mullion windows offer a sturdy window option which gives a home a classic, period look. Mullion windows are also installed as egress emergency exit windows and are appreciated as attractive window additions to any area of a home or other building. The mullion -- the vertical frame onto which the window closes -- may be included as part of the window frame or may be built into the building structure. They are generally used to fill large openings.


[edit] Operation

A mullion is vertical frame member that separates two sashes of a casement window. Casement windows with mullions can open inward or outward. They may be operated as either a crank-out or push-out window.

[edit] Mullions

Mullions can be built into the home's structure using the same construction material (brick, stone, wood) as the rest of the home. Two windows are installed on either side of the mullion and close into the mullion.

[edit] Flying or Floating Mullions

"Flying" or "Floating" mullions are integral parts of a casement window frame. When two side-by-side casements are open, the flying/floating mullion opens together with one of the sides, leaving no middle mullion visible and providing an unobstructed view of the outdoors. When the casements are closed the window resembles a standard double casement window. The lock closes into the mullion to secure the window.

[edit] Placement

Mullion windows can be used in any area of a home with a large window opening including a kitchen, living room, dining room, family room or master bedroom. Mullions are also used as egress emergency exit windows for basement bedrooms because, when open, they allow for easy passage in or out of the room.

Homeowners with a large expanse of window area may wish to place several mullion windows side by side along a wall. A group of three, four of five mullion windows may span an entire wall.

Mullion replacement windows many also be installed as part of the structure of a bay or bow window.

[edit] Benefits

Many homeowners add mullion windows to their home to enhance the home's aesthetic presentation. Grilles or custom-designed mullion windows can increase the presentation that the mullion windows add to a home's design. Other homeowners select mullion windows because of the windows' safety features and construction offer an appropriate egress escape window.

[edit] Sizes and Shapes

Replacement mullion windows are available in a variety of sizes. When used as an egress emergency exit window they must be large enough to meet the local code for an egress window. Window sizes also depend on whether the mullion window is a self-contained floating/flying mullion. In such cases it must present as a large window which is installed in a window opening that is large enough to contain the two sashes of a casement window. Replacement mullion windows which close into a mullion that has been built into the home's frame are generally comprised of only one sash.

Sizes of mullion windows may range from 10 inches wide by 15 inches high to up to 3 feet wide by 6 feet high. In addition, a homeowner may custom-order a mullion replacement window in any size.

[edit] Considerations

Homeowners may wish to consider a mullion replacement window if the remodeling project has a large rough opening and the homeowner wants to install a quality window that fills the opening, insulates the room and presents an attractive window option. Homeowner should make sure that the mullion window closes securely into the mullion if the mullion is built into the house construction to provide a weather proof window alternative.

[edit] Energy Efficiency

Mullion replacement windows are generally used for large window openings. The thermal insulating properties of the mullion window should be carefully considered to ensure that the homeowner will be able to control the room's temperature without expending excessive amounts of energy.

Homeowners can ascertain a window's energy efficiency level by checking the U-Value of the window. The U-value indicates the window insulation's resistance to heat flow. Windows with low U-Values have the greatest insulating effectiveness.

Ascertaining a window's U-Value is accomplished by reviewing the rating provided by the National Fenestration Rating Council (NFRC). High-performance replacement mullion windows can have U-factors of 0.30 or lower. The best U-Value ratings are achieved by specific triple-pane windows. The U-Value is judged by a combination of the window's framing and glazing.

Energy efficient replacement mullion windows are generally a more expensive window option but homeowners today are increasingly turning to well insulated windows as a long-term cost saving window alternative. Windows with good U-Values allow the homeowner to recoup the additional costs within four years and save much more money over the lifetime of the window.

In addition, many states offer rebates to homeowners who renovate their homes using energy efficient materials including well-insulated windows. These combined savings make well-insulated windows a good choice for long-term energy savings.

[edit] Framing

Replacement mullion windows are available in a variety of framing materials including vinyl, aluminum, wood and wood clad, fiberglass and composite materials.

[edit] Vinyl

Vinyl replacement mullion windows are obtainable in a variety of interior and exterior colors. They are a sturdy window alternative which do not require any additional maintenance. Many vinyl window manufacturers provide adequate insulating capabilities.

[edit] Aluminum

The new grades of aluminum which are available today make aluminum replacement mullion windows a good lower-cost choice for replacement mullion windows. Older grades of aluminum would contract cold and create a build-up of moisture along the inside of the window. Newer grades of aluminum are not susceptible to this problem.

[edit] Wood and Wood Clad

Wood windows can rot or warp if not painted yearly. Many wood frame window manufacturers offer wood windows with treated aluminum cladding along the exterior of the window to further insulate the window and prevent the breakdown of the wood frame.

[edit] Fiberglass

Fiberglass replacement mullion windows are a more expensive window option but present a low-maintenance window with good quality insulation capabilities. Fiberglass frames come in a wide variety of interior and exterior color selections.

[edit] Composite

Composite windows are good insulating windows which are manufactured from a hybrid of materials. Homeowners may choose from a selection of composite window materials including fiberglass with interior wood cladding, wood veneers on vinyl frames and frames made of wood chips and recycled plastic.

[edit] Glazing

In addition to the framing materials, the U-Value of a window is determined by its glazing. Window manufacturers insulate the windows' glazing in a variety of ways to increase a window's resistance to heat flow and increase the energy efficiency of the window.

[edit] Multi-Pane Glazing

Window manufacturers provide double and triple pane glazing for a variety of window framing materials including vinyl, aluminum, fiberglass, wood clad and composite frames. The extra panes add to the ability of the window to prevent heat transfer.

In addition, some window manufacturers pump insulating gases including argon gas or krypton gas into the gaps between the multi-paned windows. These gases further insulate the window's glazing.

[edit] Low E Coating

The Low-E (Low-Emissivity) coating is coated on the replacement mullion window in the factory to help reduce energy loss. Low-E is an invisible layer of metallic oxide which aids in controlling heat transfer caused by the sun's rays. A coating of Low-E can reduce a window's energy loss through the window's glazing by as much as 30% - 50%.

[edit] Accessories

Replacement mullion windows come with a variety of accessories to provide increased functionality as well as attractiveness.

[edit] Screens

Removable screens are available for replacement mullion windows. Screens for outward opening windows are installed on the inside of the window and screens for inward opening windows are installed on the outside of the window. The screens clip in and out to allow for easy cleaning of both the screens and the window.

[edit] Hardware

Operable hardware for replacement mullion windows includes the windows' locks, handles and cranks. The hardware is included in the standard window order as hard plastic though the homeowner may request, at an additional cost, either bronze or brass hardware.

[edit] Grilles

Grilles are often included as part of a replacement mullion window order. Grilles come in a variety of designs, shapes and shades. Window manufacturers can install the panes between the glass panes of replacement mullion windows with double or triple panes. In addition, other grille options include clip on grilles which can clip onto the window sash to provide a grille effect. These grilles may be removed at will when the homeowner wants to wash the grilles.

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