Window Type
There are different types of windows, each with its own functionality and appearance.
Accent or Picture Window: An accent and a picture window each have distinctive design elements. Accent windows are typically smaller, with built-in grid designs that add a decorative element to the window. You can find accent windows in various shapes, including rectangular, octagonal and oval options. Picture windows are typically rectangular, with designs that focus on maximum natural light and unobstructed views.
Awning Window: An awning window has an operable sash or panel that tilts outward along a hinge at the top of the frame, allowing the bottom of the window to open.
Basement Hopper Window: A basement hopper window is an operable window that tilts outward along a hinge on the bottom of the window frame. As the name suggests, these are common choices for basement windows.
Bay or Bow Window: A bay window and a bow window both extend outward from the exterior of a home, but each has a unique look. A bay window usually has a large, inoperable center panel with smaller operable windows fastened on each side at an angle. The construction of a bow window is similar but the angles between the center window and side windows are greater, making the window appear to bend outward rather than projecting outward like a bay window.
Casement Window: A casement window tilts outward on a hinge on the left or right side of the window frame.
Double Hung Window: A double hung window has operable upper and lower sashes. Double hung windows let you maximize ventilation by lowering the upper sash and lifting the lower sash. Warm air can exit through the top and cool air can enter through the bottom. Double hung windows often feature tilt-in sashes, allowing you to clean the window exterior from indoors.
Glass Block Window: A glass block window is an assembly of individual glass blocks. Mortar or a metal frame holds the blocks in place. While glass block windows aren’t operable, some include a tilt-in vent to allow airflow. You can find clear glass block windows, but most use obscure glass that allows light into a room while maintaining a level of privacy.
Single Hung Window: While similar in appearance to a double hung window, a single hung window has a fixed upper panel. Only the lower sash is operable. Single hung windows are available with tilt-in lower sashes for easy cleaning of the window exterior.
Skylight: A skylight functions like a window on a building roof. Skylights illuminate a room during the day, reducing the need for overhead lights. Fixed skylights aren’t operable, but venting skylights open partially to allow airflow.
Sliding Window: A sliding window has an operable sash or panel that moves horizontally rather than vertically.
Glazing Type
Glazing refers to how a window manufacturer assembles the panes or individual glass panels to build a window.
Double Pane Glass: A window with double pane glass features glass on either side of an open space. The two layers of glass and the space help reduce the transfer of sound and heat, making a double pane window a very common option for improving energy efficiency. Depending on the window, the space might simply contain air or it might contain argon gas to improve insulation.
Laminated Glass: In laminated glass, clear plastic or polymer sheets bond multiple layers of glass together. If the glass breaks the bonding layer holds the fragments in place. The design of laminate glass makes it useful for security and safety. Laminated glass also has some sound-reducing qualities.
Obscure Glass: Obscure glass has a surface that allows light to enter a room but blocks clear views into or out of the space. Obscure glass offers good privacy while adding a decorative appeal. You’ll often see obscure glass in glass block windows.
Single Pane Glass: As the name suggests, a window with single pane glass has only one glass panel. Single pane glazing is much less common than multi-pane glazing since a single pane is less efficient at reducing sound and heat transfer.
Triple Pane Glass: Three glass panes with two areas of separation provide improved resistance to sound and heat transfer compared to double pane glass.
Glass Strength
The manufacturing process and the thickness of the panes are both factors that affect the strength of the glass manufacturers use in windows.
Annealed Glass: Annealed glass is a common type of window glass. During the manufacturing process, the glass cools slowly. While this type of glass is comparatively economical, it isn’t as strong as impact glass or tempered glass. When annealed glass fractures, it forms sharp shards.
Design Pressure Rating: The design pressure (DP) rating of a window is a measurement of how well the window resists pressure, such as from high winds. The design pressure rating indicates the level of pressure, in pounds per square foot, the glass can handle before it fails.
Double Strength Glass: The term double strength refers to the thickness of the glass pane. Double strength glass is typically 1/8 of an inch thick, making it thicker and stronger than single strength glass.
High-Altitude-Rated Glass: Many multi-pane high-altitude glass windows allow the pressure of air between the panes to equalize with the outside air pressure, reducing the potential for damage to window seals and loss of energy efficiency.
Impact Glass: Impact glass or impact-resistant glass consists of a clear interlayer between two panes of tempered glass. This strong glass helps protect against debris and wind-driven projectiles.
Single Strength Glass: Single strength glass is typically 3/32 of an inch thick, so it isn’t as strong as thicker double strength glass.
Tempered Glass: Tempered glass is stronger than comparable annealed glass and doesn’t create sharp fragments when it shatters. Heat treating and rapid cooling during manufacturing give tempered glass these properties, making it a common choice for applications where safety is a concern.
Glass Insulation
Insulated windows help make a home more energy efficient. There are several techniques that manufacturers use to construct insulated windows.
Argon-Gas-Insulated Window: An argon-gas-insulated window is a type of double- or triple-paned window. Argon gas fills the space between the panes and acts as an insulator. This clear gas helps keep warm air inside during the winter and outside during the summer.
Low-E Argon Gas Window: This type of multipaned window combines a low-E glass coating with argon gas insulation to maximize energy efficiency and home comfort.
Low-E Glass: Low-E or low-emissivity glass features a coating that allows visible light through a window while blocking or reducing ultraviolet (UV) and infrared (IR) light. Reducing UV light helps protect furnishings from fading. Reducing IR light helps keep heat outside during summer and inside during winter.
Energy Factors
Understanding key factors related to energy efficiency helps you make an informed choice when shopping for windows.
ENERGY STAR® Certified: Selecting products that are ENERGY STAR® Certified is an easy way to identify energy-efficient windows and skylights for your home. ENERGY STAR® is a government-backed symbol for energy efficiency administered by the U.S. Environmental Protection Agency that provides simple, credible and unbiased information for consumers and businesses. The certification takes into consideration various energy and performance factors, including solar heat gain coefficient and U-value (definitions below). To purchase the best ENERGY STAR® certified windows and skylights for your home, first determine your ENERGY STAR® Climate Zone at the ENERGY STAR® website. Then search for the correct ENERGY STAR® Climate Zone on Lowes.com using the ENERGY STAR® Certified navigation element on the left side of the our product pages.
Solar Heat Gain Coefficient (SHGC): A window’s SHGC indicates how much heat the window allows through the glass and into a space. Windows with lower SHGC values allow less heat through the window, helping reduce reliance on a cooling system to keep your home comfortable.
U-Value: The U-value or U-factor of a window is a measurement that indicates how much heat can escape from a room through the window. Windows with lower U-values lose less heat to the outside, helping keep a room more comfortable in the winter while reducing reliance on a heating system.
Frame Material
Frame material is a factor in the look, energy efficiency, durability and cost of windows.
Aluminum Frame: Aluminum is a low-maintenance option for window frames. It’s lightweight, making aluminum windows easy to work with but is also strong, making it an effective material for large windows or windows that need to resist high winds. While aluminum is strong and doesn’t require much upkeep, it’s not the best insulating material.
Aluminum-Clad Frame: An aluminum-clad window frame has a wood core and an aluminum shell or cladding. These frames combine the low-maintenance features of aluminum with many of the insulating properties of wood.
Fiberglass Frame: Fiberglass creates durable window frames that resists warping and can stand up to adverse weather conditions. Fiberglass frames can also be effective at preventing heat loss or gain.
Vinyl Frame: Vinyl is a common window frame material. Vinyl tends to be a comparatively affordable option that offers good durability, low maintenance requirements and fade-resistant color.
Wood Frame: Wood gives window frames an enduring appeal, but requires regular maintenance to keep it looking good and to protect it from the elements. Wood insulates better than aluminum but is one of the more expensive options for window frames.
Window Balance
Window balance is a factor in how easily a window opens and closes. There are several systems for balancing a window to make it easy to operate.
Block and Tackle System: A block and tackle system in a window uses pulleys, cords and springs to reduce the effort necessary to move a window sash up and down and to support the sash when it’s open. The spring provides the tension to support the sash while the pulleys help control the tension.
Constant Force System: A constant force balance system uses tension from a coiled tape to balance the weight of the window sash. As the tape retracts, it helps lift the window sash.
Spiral System: A spiral window balance includes a spiral rod and a spring inside a tube. Rotating the rod with a tensioning tool allows adjustment of the tension of the spring to match the weight of the sash. A correct balance between tension and sash weight eases operation and helps keep the sash open.
Lock Type
There are common types of locks for windows, including latch, sash, sweep and sliding locks. You might use some of these terms interchangeably so we try to explain the different types and uses below.
Latch: The term window latch can refer to a sweep- or sash-type lock for a window or to a mechanism that holds and releases tilt-in window sashes.
Sliding Window Lock: A sliding window lock secures a sliding window closed or limits how far it opens. Sliding window locks can also work on some types of windows that open vertically. Typically, you secure the lock to a window track with one or more thumbscrews. Adjusting the position of the lock changes how far the sash can move along the track.
Sweep or Sash Lock: A sweep or sash lock is the most common type of lock for single- and double-hung windows. The rotating latch on the lower sash fits a receiving piece or keeper on the upper sash, preventing either sash from moving. Other types of windows use a similar mechanism where the keeper attaches to the window frame. Some sweep locks are keyed for extra security.
Project Type
Manufacturers build windows for two different types of projects: new construction and replacement jobs.
New Construction: As you might guess from the name, builders typically install new construction windows when building a house or an addition to a house. A new construction window has a flange or nail fin around the frame to allow the installer to fasten the window to the sheathing of the structure before installing siding or brickwork.
Replacement: Replacement windows don’t have a nail fin and allow installation without removing the exterior siding, etc. The installer secures the window by driving fasteners through the window frame and into the frame elements of the window opening.
Other Terms
There are a few other common window terms you may see when shopping for windows.
Exterior Extension Jambs: An exterior extension jamb installs around the exterior of a window unit. The extension allows the window to be inset from the outside wall while creating a finished look between the window frame and home exterior.
Interior Extension Jamb: An interior extension jamb fits around the inside of a window jamb to create a finished look in the area between the window frame and the interior wall or window casing.
J-Channel: J-channel is a type of trim work that has a J-shaped profile. In window installation, J-channel trim fits over the ends of the siding on each side of a window to create an perfectly framed and finished look.
Mulling: Mulling is a method of connecting individual window units together to fill a large window opening.
Nail Fin: A nail fin is a flange on the outer edge of a new construction window frame. Fastener holes in the nail fin allow an installer to nail or screw the window to the sheathing of a home or other structure. The combination of the nail fin, house wrap, flashing and sealant help prevent wind and water from entering at the window opening.
Sound Transmission Control (STC) Rating: The STC rating on a window indicates how well the window prevents the transmission of sound. STC ratings range from zero to 100. The higher the number, the better the window blocks sound transmission.