There are two fundamental types of windows, moveable and fixed. Moveable windows may slide, pivot, or be hinged. Fixed windows range from the standard picture window to custom framed windows in virtually any shape desired that may be a focal center for a home’s décor.

Moveable Windows

Double-hung: This type of window is the most common in the United States. Two sashes slide up and down past each other in tracks. When open, they are held in place by counterweights, a spring balance, or a friction device. Depending on the type, both sashes may move or just the lower one, in which case it is a single-hung window. At best, only 50 percent of the window can be open at any time.

Millions of homes across the country still have older double-hung windows that operate with cast iron counterweights and pulleys hidden in the side jambs. The weights vary in length depending on the weight necessary to counterbalance the window. They are separated by a narrow strip of wood called a pendulum to keep them from knocking into each other.

If the pulleys stick or the sash cord breaks, the weights must be removed through an access panel in the jamb. Because of their complexity, these windows are no longer made. Newer double-hung windows operate with a variety of tension spring balances or friction devices.

Double-hung tilt: For decades, if not centuries, homeowners have complained that the biggest problem with double-hung windows was cleaning them. Inside, no problem. But cleaning the outside meant partially opening the top or bottom and bending an arm like a contortionist to reach a pane. The unsafe alternative was to climb out onto the roof.

In recent years, window manufacturers have begun making double-hung windows with one sash that can be readily removed. It is commonly called the double-hung tilt or tilt-out. By removing one sash, the one still in place can be much more easily cleaned.

Sliding: These windows move horizontally within guides that keep them positioned. Either one or two sashes may slide in the frame. They may ride directly on the frame, on wheels, or be suspended by overhead rollers. The exterior part of the groove containing the sliding sash contains small weep holes to drain rainwater than runs down the window. Sliding windows are often longer horizontally than they are tall, which makes them easier to move. Long, narrow sliding windows are commonly found high on bedroom walls to simultaneously provide privacy and light.

Casement: A casement window operates essentially like a door. It is hinged on one side and can swing either in or out. It is operated by a crank handle and gears and can be opened 100 percent or angled to catch breezes. Because a casement window does not slide past any other part, it seals well when closed.

Because casement windows open fully, they are often preferred in bedrooms where at least one window must provide a minimum opening that is 24 inches wide by 22 inches high. Not only does this requirement allow people in the room to escape in case of fire, but it also provides sufficient space for a firefighter to crawl through while wearing an oxygen pack.

If a casement window opens near a deck or walkway beside the house, it may present a hazard to passersby. Conversely, inward-opening windows may catch on curtains. Inward opening casement windows can have a screen mounted on the outside. Windows that open out, however, have screens on the inside that sometimes must be custom made to fit around the crank mechanism.

Bay and bow: Bay and bow windows are similar in that both project out from the house and have three or more panes of glass to provide a view on both sides in addition to the front. The bay window has a middle window and two side windows that angle off at 45 degrees from the center window. Usually the side windows open and the center window is fixed. The bow window has several panes arranged in a sweeping, outward curve, with some of the windows operable.

Awning: These windows are hinged along the upper sash and tilt out to open. They can be opened in wet weather and still keep rain out.

Hopper: Similar to an awning window except that it is hinged on the lower sash and tilts in. It, too, is useful for providing ventilation while keeping rain out.

Jalousie: Like a venetian blind, the individual glass blades move simultaneously when a jalousie window is cranked open or closed. These windows are comprised of a series of glass strips that overlap when closed. Because rain will fall off them when partially open and still allow air to circulate, they are popular in tropical climates.

Fixed Windows

Picture window: A single large expanse of fixed glass may evoke memories of houses built in the 1950s. To avoid that, large fixed windows are now commonly combined with several smaller adjoining windows that open for ventilation.

Custom designs: Fixed windows may be of almost any design, including curved, triangular, round, octagonal, or hexagonal. Such windows can be installed wherever desired, between studs in a wall, in an attic, or above a door.

Windows are made from wood, aluminum, steel, vinyl, vinyl-clad wood, aluminum-clad wood, fiberglass, and composite materials. Confused? Most people are, particularly when it comes to deciding which one is best for their house. Each material has both positive qualities and drawbacks that should be considered when choosing windows. Here is some background on several common window materials:

Wood: For centuries, window frames have been made of wood, and it still remains a leading choice for premium windows. Most commonly, windows are made from Ponderosa pine or Douglas fir, but they may also be white pine, redwood, cedar, or cypress. The wood must be clear, meaning it contains no knots that could weaken the wood or be difficult to paint or stain.

Wood has better insulating qualities than metal. Moreover, water will not readily condense on wood, as it is prone to do on metal. Extensive condensation can lead to wood rot problems around the window.

Wood-framed windows may be double-hung, sliding, casement, or any of the other varieties. They can be stained or painted to match your house’s décor, which is one advantage over aluminum windows, which cannot be painted. On the other hand, wood windows must be stained or painted at regular intervals to protect them from the elements.

Most wood windows are made in a variety of stock sizes. This system works well in new construction where carpenters frame the rough opening for known window sizes. But if you want to replace a window, it may be difficult to find the same size because different manufacturers have different stock sizes.

Aluminum-clad wood: This combination is a popular choice among homeowners and professionals because it combines high quality materials with low maintenance requirements. The exterior side is covered with aluminum that comes in a variety of colors baked into the finish. It provides excellent protection against the elements and does not need painting. The interior side is made of wood and can be either stained or painted to accompany the home’s décor.

Vinyl-clad wood: These windows are similar in style and function to aluminum-clad wood windows, only with a vinyl exterior. The vinyl comes in a more limited choice of colors, such as white, brown, and beige, but is highly resistant to the elements.

Aluminum: These light metal frames are strong and generally less expensive than wood frames. Lower quality aluminum windows readily transfer cold, making them a poor choice in areas of wide temperature swings. Newer models have a strip of plastic or rubber in the frame called a thermal break that is designed to reduce heat or cold conduction.

Aluminum windows in recent times are commonly finished with a baked enamel paint in white or bronze. Older aluminum windows were anodized, which means given a protective film coating by electrolysis. These frames will eventually corrode, however, especially in a salt air environment. Periodically coating the frames with auto wax can help prevent corrosion.

Steel: Many older homes have steel window frames, but these windows are currently found primarily in commercial buildings where higher fire safety standards are required. Although durable, they require considerable maintenance, including regular painting. If not painted, they will soon rust.

Fiberglass: These tough window frames are made from materials similar to the composite bumpers used on many cars today. The frames are made from a fiberglass/composite material, usually a polyester resin, that is strong, maintenance free and energy efficient. Although usually higher priced than vinyl windows, fiberglass frames can be painted, something that cannot be done with vinyl.

Vinyl: These windows came into their own as energy-conscious homeowners began looking for ways to retrofit their homes and add double paned insulated glass. Homeowners could suddenly change only parts of a window or the whole thing, depending on their needs. If the double-hung window tracks were worn out, they could install just vinyl tracks with built-in counterweight springs. Or they could put in new sashes if the frames were in good condition, or replace the whole window unit.

Vinyl frame windows usually run about half the price of wood windows. A honeycomb effect in the extruded vinyl frame provides insulation through dead air space. A chief advantage of vinyl windows is that they can be readily constructed to fit any opening, making them a top choice for inexpensive window replacements. The colors are limited but they do not require painting.

But not all vinyl frames are equal. Some manufacturers buy the vinyl extrusions as cheaply as possible and then assemble the windows. To judge quality, look at the extrusion in section. The best ones will have up to 13 chambers inside divided by webs. Lesser ones will have only four or five chambers. While the chambers offer insulating qualities, it’s the webs that provide the strength. The more webs, the stronger the window.

Storm windows are designed to both protect the windows and further reduce air infiltration. They are often custom designed to fit precisely over your existing windows and may be single or double paned, depending on your energy saving needs. Storm windows offer an added benefit of reducing exterior noise, particularly if they are double paned.

Storm windows are made from aluminum, steel, wood, or vinyl. They may also be wood that is vinyl or aluminum clad on the outside, with colors to match your house’s exterior finish. Some come with sliding windows that have screens, allowing you to open your windows for fresh air without having to remove the storm windows during the summer months.

Before installing new windows in your home, check local code requirements. Local codes overrule national codes, and they may differ from some basic national regulations.

Minimum window requirements in a habitable room are as follows:

• 20 inches wide
• 24 inches high
• 44 inches maximum from bottom of window opening to floor

This requirement provides sufficient room for people to escape in case of fire and for a firefighter to pass through the window while wearing an oxygen pack.

Safety glass must be used in certain situations. Safety glass includes laminated glass with a minimum 7/32-inch plastic interlayer, approved plastics, or tempered glass. Safety glass is required in the following areas:

• Sidelights within 12 inches of a door
• Windows within 24 inches of a door
• Any glass less than 18 inches from the floor
• Sliding glass doors
• Framed and frameless glass doors
• Bath and shower enclosures.

Tempered glass must also be used if all (not just one, but all ) of the following conditions exist:

• Window area is greater than 9 square feet
• Top edge of glazing is more than 36 inches above the ground or floor
• Lower edge of glazing is less than 18 inches from the ground or floor
• Window is within 36 inches of a walkway.

Other general codes rules state that

• Glazing in a habitable room must equal 1/10 of the floor area
• Ventilation (open window area) for a habitable room must equal 1/20 of the floor area
• No window is permitted in a wall less than 3 feet from a property line.

In seeking to understand energy efficiencies in windows, you need to understand these common descriptive terms:

U-value: This value is the most important rating for window energy efficiency. It measures the rate of nonsolar heat transfer from one side of a window to the other. It takes into account both infiltration rates and heat transfer for the entire window. The lower the U-value, the greater the window’s resistance to heat flow. Thus, the larger your heating bill, the more important is the U-value. In cold climates, you should select windows with a U-value of 0.35 or less. In hot climates, choose a U-value of 0.75 or more. And in mixed climate zones, where both heating and cooling are of equal importance, select windows with a U-value of about 0.40.

Solar heat gain coefficient (SHGC): This rating measures the solar heat radiation through a window and is expressed as a number between 0 and 1. The lower the heat gain coefficient, the less solar heat a window admits. In areas with high summer heat, choose a window with SHGC values of 0.40 or less. In moderate climates, with little or no air conditioning needs, select a value of 0.55 or less. In northern and colder climates, where you want the winter sun to add solar heat to the house, choose 0.75 or more.

Air leakage (AL): Gains or losses in heat occur through openings around window units because of insufficient sealing or weather stripping. AL measures such gains or losses in cubic feet per minute through 1 square foot of window unit area. The lower the figure, the less air that can pass through the window unit. Choose a window with an AL of 0.30 or less.

Visible transmittance (VT): This indicator measures the amount of daylight transmitted through a window. The ratings are between 0 and 1, and 0.70 or better indicates a high capability for daylight to enter your house. Single glazing allows the most, triple glazing the least. Window tinting, of course, will reduce the VT rating.

Low-E coating: Low emissivity coating is essentially an invisible metallic coating that reflects back the higher level of heat. Thus in summer it reflects solar heat back to the outside; in winter, it reflects room heat back into the house. Low-E coating is used only on double or triple pane glass and is applied so it faces the gap between two panes.

Argon and krypton gases: These are inert gases sealed between panes of glass. Because the gas molecules are heavier than air molecules, heat takes longer to transfer through the gas. This in turn reduces the transmission of heat or cold from one pane of glass to the next.

R-value: The higher the R-value, the better the window’s resistance to conductive heat loss. It is the inverse of U-value—the lower the U-value, the higher the R-value. It is not as accurate as the U-value in judging a window’s overall energy efficiency.

Different ratings are shown on the National Fenestration Rating Council tag on a window. Here is an example:
 

National Fenestration      Rating Council                            Incorporated			Independent Administrator
AAA Window Company
Manufacturer stipulates that these ratings were determined in accordance with NFRC procedures.
Energy Rating Factors	Ratings Residential /  NonResidential		Project Description
U-Factor Determined in Accordance with NFRC 100	0.34	0.32	Model 1000 Casement Low-e=0.4 Argon Filled 0.5" gap.
Solar Heat Gain Coeffiecient Determined in Acordance with NFRC 200	0.31	0.32
Visible Transmittance Determined in Accordance with NFRC 200	0.51	0.55
NFRC ratings are determined for a fixed set of environmental conditions and specific product sizes and may not be approperiate for directly determining seasonal energy performance. For additional information contact:

 

1. Muntin 2. Lights 3. Upper Sash 4. Stop 5. Rail 6. Stile 7. Inside Casing 8. Lower Sash 9. Apron 10. Stool 11. Frame

Despite the wide variation in styles, windows generally have the following parts:

The window frame is attached to the rough opening in the wall.

The sash moves within the frame. It may slide or be hinged.

The sash contains panes of glass, called lights.

The lights may be divided by muntins.

The space between two adjoining windows is a mullion.

The sash consists of the vertical stiles on each side and the horizontal upper and lower rails.

The window is held in place by an inner stop on the sides and top.

The trim around the window is called trim or casing.

The window sill on the outside is sloped to carry water away. The inside part, although often called the sill, is the stool.

The trim beneath the stool is the apron.

Windows and Warranties

Window warranties can vary immensely and should be read closely. For example, many window manufacturers offer a 10- or 20-year "seal failure" warranty. It may sound great—20 years—but it only covers the material costs. You would pay for someone to come to your house, take out the window, make the repairs, and reinstall it. Look for warranties that include both materials and labor.

Watch out for wording in the warranty that you don’t understand. References to something like "material obscurant of vision" may mean the manufacturer is saying that if the window clouds just along the edges, which does not materially block or obscure the vision, then the manufacturer is not going to make repairs.

Be wary of manufacturer’s warranties that exclude problems caused during installation or by owner-paid shipping and crating, even by their employees. Because poor installation can result in leaks of air and water around the window, ask whether the manufacturer provides certified installers to guarantee the installation quality.

When selecting windows, check how long the manufacturer has been in business. The longer the better. Some companies offer "lifetime" warranties that mean nothing because they are out of business in a few years. Ask for several recent references and check them out. Don’t be hesitant to call the Better Business Bureau and ask if any complaints have been lodged against the manufacturer. After all, you may be purchasing thousands of dollars worth of windows.

Glass Details

Various agencies monitor the quality of the glass in windows and how well it performs. One such agency is the nonprofit Insulating Glass Certification Council, which tests the durability of insulating glass seals that window manufacturers use. The IGCC rates durability of glass by assigning it one of four categories: CBA, CB, C, or unrated. The CBA rating is the highest. If a window dealer has unrated windows, you are not getting the best grade of insulated glass.

Here is a primer on glass, which may be of particular interest if you desire to preserve a house’s historic qualities.

Sheet glass: This type of glass may still be found in houses built before 1940. It is recognizable by its wavy distortion and obvious imperfections. It was made by allowing a ribbon of molten glass to spread into a wide sheet before it cooled. This air-cooling technique gave the glass a bright sheen that is not seen on standard glass today.

Plate glass: This type supplanted sheet glass and was made by rolling molten glass flat and then polishing it. This technique removed distortions and it could also be made much thicker and stronger, which was of particular value in large store windows.

Float glass: The most common type of glass now produced is float glass, which is made by pouring molten glass over a bed of mercury. The glass floats on top of the mercury and cools with no distortions.

Tempered glass: This type is glass highly resistant to breaking and when it does, it crumbles into thousands of tiny pieces with no sharp edges. It is made by reheating float glass and then cooling it quickly. Tempered glass is normally required within 3 feet of doors. It cannot be cut but instead must be made specifically for your needs.

Laminated glass: Also a safety glass, it is made by laminating clear plastic between two sheets of glass.

Electronic privacy glass: Liquid crystals are suspended between two panes of glass and connected to an electrical circuit. When the crystals are not electrified, they merge into random patterns that give the glass a frosted appearance. When a current passes through the crystals, they align themselves and the pane is clear.

Window Replacement

Any window can be replaced, but the new window will have to fit the existing rough opening. Custom made wood or wood with vinyl or aluminum cladding will be more expensive than stock windows. Check with local suppliers to see if they have stock windows that will fit your existing openings.

Because of costs, the less expensive but serviceable vinyl double-hung windows are the number one choice for replacement windows. Hundreds of companies small and large make vinyl windows in all styles to fit whatever opening you have.

In judging a vinyl replacement window, the key thing to look at is a cross section of the extruded vinyl the company uses to make the window sash. You will see that the interior is honeycombed, with a network of hollow areas and webs. The more webs, the stronger the sash will be.

But a total window replacement is not always necessary to upgrade your windows. You can add one or more of the following vinyl elements to your double-hung windows (regardless of what the original window was made of):

• Vinyl track inserts: If your existing double-hung windows are difficult to move up and down, new vinyl tracks on each side of the existing window sashes may be the answer. The existing windows are removed and the vinyl tracks installed on each side. The tracks contain built-in counterweight springs to hold the window open. The windows must be trimmed to fit, however, so ask the company that sells the vinyl replacement parts if they will trim the windows.

• New sashes and vinyl tracks: If your existing window sashes are too far gone, you can replace the sashes and install new vinyl tracks at the same time. The new window sashes may be all vinyl or may be wood windows that fit the existing openings. The glass is normally double pane. Another advantage is that the double-hung windows readily snap out of the vinyl tracks for easy cleaning.

• Vinyl inserts: With these windows, the new vinyl sashes are contained in a single vinyl unit that fits within the existing window frame and trim. They are a common choice when both window sashes are in poor condition. The advantage is that they can be fairly easily installed without having to remove interior or exterior trim. The drawback is that they are obviously vinyl replacement windows that don’t match other windows in the house.

• New window unit: This option is a large job because both interior and exterior trim must be removed and then replaced after the new window unit is installed. The new unit can be the material of your choice, including wood, if you find stock sizes that fit your rough opening. Vinyl is a popular choice because it can be readily fabricated to fit any opening.

Window Maintenance and Repairs

Here are some common problems with windows and how to fix them:

Windows painted shut: Slip a wide-bladed putty knife or something similar between the frame and the sash to cut through the dried paint. There is also a neat little tool called a Paint Zipper that does it better, available at many hardware stores. You may have to work hardest along the bottom edge where paint ran down. Slide the blade all around the window to clean out old paint.

Windows don’t slide well: Open the window and rub the affected area with candle wax.

Double-hung windows won’t stay open: The sash cord is likely broken or has come untied from the weight. To fix it, you have to remove the lower sash, which means removing the inner stop. Since the project just gets more complex, go buy vinyl track inserts and slip them in place on each side of the sashes and be done with it.

Double panes fogging up: When this happens, the seals are leaking. Have them repaired right away because the moisture that collects inside the panes can eventually etch the glass beyond repair. Look carefully at the spacer between the panes, usually along the bottom edge of the window, and you may see the name of the window manufacturer. Ask if the warranty is still in effect, particularly if it is a "lifetime" warranty.

Water leaks around windows: If a window was not flashed properly on installation, it may very well leak. Flashing refers to the bent metal that slips under the siding above the window and then out over the top of the window. Without proper flashing, rain can work its way behind the window and then appear in a number of different places. It could run down from the top of the window or under the sill, or even down by the floor. If you have a leak on a wall and there is a window nearby, suspect the flashing. For quick relief, you can caulk between the window and the siding, but it will not be permanent.