Window Mulling

Window mulling refers to the process of joining two or more windows together. This may be done in the factory, or on a job site as a home is constructed, remodeled, or its windows are replaced. The benefit of mulling, or joining windows together is to create a larger focal point and natural light in the home, like in the case of a group of windows in succession to frame a fantastic view, or to create architectural interest in a great room, a living room, a foyer or other area of the home. Because of the weight of glass and manufacturing equipment and shipping size limitations, there’s often a limit to how large a single window unit can be and remain structurally sound. Mulling, or joining groups of windows together allows you to maximize your view, while maintaining your home’s structural integrity and residential window product performance.

The rating of mulled combinations may be lower than the individual unit rating. It is important to verify that the mulled combination rating meets your project's building code requirements.

Some windows include exterior cladding

Some windows also feature exterior cladding—a covering or “skin” like those made of aluminum or vinyl, applied over the window frame and or sash, to help protect exterior surfaces from environmental conditions, or for aesthetic purposes. For example applying aluminum cladding over a wood window helps provide added protection with a wide range of exterior color or texture options for design appeal.

Wood windows made from a range of species

Wood windows can be made from a variety of species of woods, from readily available renewable resources like pine, a soft wood, to hardwoods like oak, cherry, or mahogany, or other woods. Modern wood windows are typically factory treated for added protection against damage from moisture or insects.

Window laminates offer unique looks, plus help protect from elements

Laminates can also be applied to residential window sashes and frames to provide different looks. For example, laminates can provide the look of simulated wood grain, to various color or texture options. For example, a solid-colored laminate could be featured on the exterior of a window, with a wood-grain effect, an embossed texture, or a metallic look on the interior. In addition, laminates applied on residential window framing material can help protect against dirt, chemicals and environmental pollutants.

Window hardware options abound

Hardware is used to open, close and lock residential windows, or to provide decorative accents. Residential window hardware comes in a variety of styles and finishes, including some specialized options, like automatic-locking window hardware, or that which is easier for those with limited mobility to operate. For example, some hardware is designed for easier use by the elderly, or those with arthritis.

Double-hung windows may include sash lift hardware options. Sash lifts are handles placed on the interior of the lower sash of the window that make it easy to grip the lower sash to open and close it. Plus sash lifts often replicate the look of earlier eras in architectural design. Some hardware, called spoon hardware because its shape literally resembles the bowl of a spoon, is another option available to add a historic look to today’s windows.

Some windows can be equipped with egress hardware, allowing for a wider opening of a window unit. Check with your local building code officials to learn more about egress requirements for your home’s area.

Optional hardware also includes window opening control devices (WOCD) to help prevent accidental falls through windows, and other devices that simply limit the window from opening greater than four inches.

Consider the window warranty

Before you consider after-market options to your windows such as window films, thermal blinds, etc., consult the warranty of your window manufacturer. Keep in mind that some after-market products may void the original window manufacturer’s warranty, so consult the window warranty before you modify the window or its performance.

Decorative elements accent the look of residential windows

Residential windows can include grilles, sometimes also called grids or muntins. These create the look of individual panes of glass, but provide greater energy efficiency than single panes of glass connected together.
Grilles can be permanently applied to the exterior and interior of window glass, be permanently placed and sealed between panes of glass, or be removable.

When grilles are placed between panes of glass, it makes it easier to clean a window’s interior and exterior glass surfaces, compared with cleaning smaller, individual panes of glass separated by a grille or framing material.

Glass options can improve energy efficiency, privacy, reduce sound

Residential windows are available with a variety of glass, often called glazing options, like low-E (low emissivity) insulating glass, obscure glass or clear glass. Other types of options include double- or triple-pane insulating glass options, tempered or safety glass, or impact-resistant glass for security or hurricane zones.

Obscure glass may be frosted glass or textured (patterned) to help provide privacy, for example, in bathrooms or exterior doors.

Clear glass is a basic option that does not incorporate coatings to help improve a window’s energy efficiency. Clear glass allows heat and the sun’s rays pass through the glass, which can fade interior furnishings and reduce a home’s energy efficiency.

The type of glass used in residential windows can also impact daylighting. For instance, in the south, better glare control and lower levels of transmitted light may be desired. Certain low-E glass products help control bright light and glare. View the daylighting page for more information.

Screens help keep insects out

Residential windows may feature screens to help keep insects out of a home. Keep in mind that insect screens are not designed to withstand the weight of a person, so don’t lean on screens and keep child’s play away from windows, for safety’s sake.

Screens may be installed on the exterior of a window, as is often the case in double-hung windows, or on the interior of a window, as is typical for casement or crank out windows. Some screens are known as disappearing screens, because they roll out of sight when not in use, or because the screen material is so transparent is appears to be virtually invisible.

Screens may also be applied to the exterior of a window to help control light or the reflection of it.

Many types of screen materials are available for residential windows, ranging from aluminum, to fiberglass, to other transparent screen materials.

The sounds of silence

Residential windows can also help reduce sound transmission, providing peace and quiet and peace of mind inside your home. The STC rating stands for sound transmission class. What that means is the window’s ability to help reduce outside sounds is evaluated. Refer to AAMA 1801 for more details.

OITC stands for outdoor indoor transmission class, similar to STC, but based more on typical outdoor sound frequencies. STC relates to indoor sound levels. STC is more commonly known, but OITC is a newer rating system that’s increasing in prominence.

Outdoor sound frequencies span the range of low frequency sounds, like the rumble of a dump truck, the sounds of aircraft overhead, or a bass from a car’s stereo system.

Improved indoor air quality

Residential windows also impact indoor air quality, helping keep out dust and dirt. Plus, the type of windows that open, called venting windows, help refresh a home when they’re opened to welcome in fresh air.

Beautiful, durable finish options to choose from

Residential windows include a variety of factory-applied exterior finishes, like those for specialized corrosive conditions caused by salt water sprays in seacoast applications, or other harsh environments.

Other types of finishes include factory prefinished options applied to wood, fiberglass, vinyl, or aluminum windows. Finishes for residential windows can range from paints or stains, to other types of coatings.

Depending on the material they’re made from, some residential windows, like wood windows, can be purchased unfinished, to be painted, stained or sealed on the job site. Some residential windows, like vinyl windows, can include factory-applied films that replicate the look of wood grain or metallic finishes.

Fiberglass windows are often factory-finished, reducing the need for painting on the job site. Vinyl windows require no additional finishing. Some vinyl windows are available with painted exterior or interior finishes to expand available color options for the homeowner.