Modern windows provide more than light and a view of what’s going on outside your house. Not only are they an architectural enhancement, but they also can provide insulation, ventilation, privacy, safety and a reduction of your home heating and cooling bills. Some of the most common windows used in residential housing are single-hung, double-hung, casement and awning, bay and garden, bow, slider, transom, picture, storm, egress, skylight, hopper, glass block and jalousie. As is evident from their names, some of these have specific functions. Windows can be made in stock or customized sizes and they are also found in different geometric shapes such as triangles, squares, rectangles and circles.
In the United States, the most commonly found and the most affordable are single-hung windows. The bottom window panel or lower sash moves up and down while the upper sash does not, so when the window is open the lower sash moves up on the inside of the house to cover the upper sash. In double-hung windows, both sashes can be raised, lowered and tilted for easy cleaning.
Casement windows are hinged, and are opened by turning a crank that swings the solid-paned window out to the side. These windows provide excellent insulation because they do not have separate pieces and breaks between the pieces. They are very good for ventilation. An awning window keeps out rain when cranked open—it creates a water-resistant awning.
A bay window, which is a center window flanked by a window on either side at a 30-40-degree angle to the center window, protrudes from the house and creates a small interior shelf below the window. Garden windows are bay windows meant to hold plants and are similar to little greenhouses. They protrude from the house and also provide sunlight for your home. Bow windows, often found in Victorian houses, are custom windows that are curved in a circular arch outside the house. Bows are much more expensive than bays.
Sliding windows usually consist of two sections; one window opens and slides over the other. These windows provide ventilation and are great for rooms with low ceilings.
Transom windows provide decorative accents and are often installed over entrance doors and sometimes over other windows. They may be semi-circular, rectangular or square. They let in light and provide ventilation as they can be opened like awning windows to allow air to enter the house.
Picture windows bring the outside view into your home; however, they do not provide ventilation or a means of emergency escape because they consist of a single pane of glass without breaks or frames.
Storm windows are installed outside, over existing windows. They protect against heat loss and drafts because they are constructed of flat panels without breaks. This construction cuts off ventilation. Storm windows are affordable and easy to install and are removed and rehung seasonally.
The purpose of egress windows is safety: a way to escape in an emergency when you are blocked from normal means of escape, such as doors. These windows are usually found in basements but must be created and installed in compliance with local fire codes.
Skylight windows come from the roof and allow light into a room; they rarely open but can open to ventilate a room. Expensive!
Hopper windows operate with cranks. They open from the top and tip down with an upward slant. They are often found in basements and bathrooms. They provide excellent insulation because, when closed, they seal up against the frame. They also prevent entry of debris into the house.
Glass block windows do not open. They provide privacy and come in frosted, patterned or clear glass. But they are expensive to replace.
Jalousie windows consist of slats of metal or glass that open and close like blinds and are operated by cranking a lever. They allow air into the house but are not good at providing insulation.
Energy-efficient windows with the Energy Star rating may save significant amounts of money for the homeowner, will insulate, and will diminish outdoor sounds from entering the house. But how well these windows work to achieve these purposes depends on several factors.
Energy-efficient windows are constructed of several glass sheets divided by spacers that create air pockets between the layers of glass, which are sealed to prevent the escape or entrance of air. The windows are filled with efficiency-enhancing gases such as argon and krypton. Sealed gases help to reduce heat transfer from one glazing layer to another, which also reduces the possibility of exterior and interior condensation on the windows.
Low-e or low-emissivity coatings keep heat in your home in winter and outside in summer. Exterior low-e coating allows sunlight to enter the home while keeping out ultraviolet and infrared light and cutting down on glare. In areas where heat gain is desired, low-e coating is used to trap heat inside as it allows the full light spectrum to enter, thereby creating a greenhouse effect that keeps the home very warm when it is cold outside Therefore, Energy Star windows for Northern climes are designed for the entry of infrared light into your home so that heat is generated by trapping warm air inside the house. These windows are double- or triple-paned. But Energy Star windows for Southern climes are different: they are designed to keep heat outside the house.
The VT rating (visible transmittance) of a window shows how much visible light passes through the windows. So if you install low-e coatings you will be blocking some light from your home because low-e windows are tinted and have additional layers of glass. This means that you will be using more interior lighting during the day, thus increasing your electric bill.
The U-factor, which is measured in Btu/h, measures the rate of heat transfer as well as indicating how good a job the window performs as an insulator. For colder climes, choose a low U-factor, which indicates better thermal resistance, because the U-factor is the rate at which a window conducts non-solar heat flow. A low U-value indicates that the window does a better job of keeping out heat and cold so it is good for temperate climes with both hot and cold seasons.
Solar Heat Gain Coefficient (SHGC) measures how well the window blocks sunlight-generated heat.
In our temperate climate, with both hot and cold seasons, choose windows with low U-factors and low SHGCs in order to maximize energy savings.
Installing an energy-efficient window will prove to be ineffective unless the window is paired with an energy-efficient frame. Aluminum windows are the least effective because they are very good conductors of heat. Therefore, consider fiberglass, wood, vinyl or composite instead of aluminum.
Before buying these windows, perform a home energy audit to determine which parts of the home need energy-efficient windows and where in the home they are not needed.
By Vivian J. Oleen
Vivian J. Oleen is an associate broker at Sopher Realty.