is an important part of a window's overall energy efficiency. The core of determining the overall energy efficiency of a window, including the interior and exterior window framing, is the U-Factor. The U-Factor rates the complete window ensemble. The lower the U-Factor, the more energy efficient the window.
Purchasing windows certified with an appropriate U-Factor for your climate is assurance of a well-performing window; however, window frames require some serious scrutiny, regardless of the U-Factor.
Maintenance is a critical issue. Some window frames are maintenance free, while others need annual attention. Lifestyle and tolerance for repair and restoration should determine the window frame you choose, along with energy efficiency and budget.
Fiberglass and Composite Window Frames
Fiberglass frames can be glass-fiber-reinforced polyester or other Fiberglass composites. Choose an insulated Fiberglass frame to achieve or surpass the thermal efficiency of wood - not all Fiberglass frames are insulated. Choose a Fiberglass frame without metal spacers and rubber gaskets. Instead, inquire about silicone foam or polymer, and butyl-wrapped materials. Because Fiberglass composite frames are new to the marketplace, it's uncertain how color choices will stand up to long-term weathering. Darker colors may fade. When purchasing, look for uniform color throughout the frame.
Fiberglass is not the only composite frame. Composites of wood particleboard, wood polymers and a mix of resins (similar to the natural resins used in plastics) are being used to make hybrid frames. Window frame technology is moving at lightening speed and composites promise many new choices in the future.
Advantages of Fiberglass Composite:
• Insulated Fiberglass is highly energy efficient
• Structurally strong
• Virtually maintenance free, if not painted
• Will not swell, warp, or rot
• Priced between vinyl and wood, but affordable
• Smaller profile, fits directly to brick or stonework
Disadvantages of Fiberglass Composite and other composite-frame materials:
• A relatively new option - availability may be an issue
• More expensive than vinyl
• May be available only in limited colors
• Can be almost as expensive as the most expensive hardwoods
• Due to fragile joints, frames must be handled carefully at installation
• Perhaps difficult to repair
Vinyl-Clad Wood Window Frames
Vinyl-clad wood frames are considered an equal insulator to wood frames.
• The strongest of all residential windows
• Highly energy efficient
• Exterior is wood covered with a thin vinyl coating
• The interior frame is natural wood
• Virtually maintenance-free
• More expensive than wood - the most expensive of all the options
Wood Window Frames
Wood, while undeniably the most aesthetically attractive choice, needs attention to detail and annual maintenance to extend its lifespan. Rotting wood or debris in cracks should be removed with a pointed object (like a screwdriver), and then filled with epoxy putty. When purchasing new wood windows, ask the manufacturer or vendor if you can expect tight-fitting joints, unblemished surfaces and invisible finger joints. If the answer is yes, check them when they are delivered and reject all that do not meet your standards.
Advantages of Wood Frames:
• Highly energy efficient if properly treated for the life of the window
• Durable and strong
• Readily available and easily customized
• Any color or stain is possible
• Most hardwoods can be used
• Still considered the gold-standard - the classic window
• Expensive, but not as expensive as vinyl-clad wood
• High maintenance - annual maintenance required for long-life
• Stain or paint required every 3 to 5 years
• Lower life expectancy due to wear from sun, wind and moisture
• If not properly protected from moisture, can swell, rot, warp and stick
Vinyl Window Frames
Vinyl PVC means poly-vinyl chloride. Shop for vinyl window frames that are manufactured with a thermal break. The thermal break is usually an internal metal network that strengthens the window, as well as improving its energy efficiency. Look for joints that are heat-welded rather than joined with screws or other fasteners, and a uniform color throughout the frame.
Advantages of Vinyl Window Frames:
• Lower cost than wood or aluminum
• Low maintenance - never needs painting
• Impervious to the elements
• Frames can be built to fit any size opening
• Many frame styles to choose from
• Can be cleaned with a natural bristle brush
• Superior insulation - an interior honeycomb structure boosts insulation capability
• Vinyl window sales are growing rapidly due to energy efficient performance
• Not very rigid - needs internal hollow chambers; the more chambers the better
Aluminum Window Frames
Thermally improved frames are the best of aluminum window frames. A "thermally improved" frame decreases heat loss and improves energy efficiency by the addition of a non-conductive material between the aluminums on the interior and exterior of the window. This addition is known as a "thermal break." Thermally improved aluminum window frames are superior to standard aluminum frames.
Aluminum framed windows should be considered only with a thermal break. The thermal break in aluminum windows is usually a strip of rubber or plastic, placed between the inner and outer frame. The thermal break lowers the ability of air to pass through the aluminum. Without the thermal break, the window will not be energy efficient.
Advantages of Standard Aluminum Window Frames:
• Light-weight, durable and strong
• Low maintenance
• Do not absorb water
• Do not rust or rot
• Resistant to warping and sticking
• Fits directly to brick or stonework
• Works well in warmer climates
• Can be cleaned with a natural bristle brush
• Less expensive than wood or composites but more expensive than vinyl
• Considered the most secure of all window frames
Disadvantages of Standard Aluminum Window Frames:
• Lose heat easily, reducing the energy efficiency of the entire window
• Susceptible to condensation
• Can feel cold to the touch
• Fewer suppliers - may be difficult to order