WINDOWS 101

Framing Material

The second consideration with respect to durability is the type of frame material the window product has. Many different frame materials are available, and they are briefly discussed below, taking into account durability, costs, and benefits. Please note that the material of the frame has a major impact on the thermal characteristics of the window. This subject will not be discussed here since the energy performance ratings provided by the NFRC label already incorporate the thermal properties of the frame in the results.

Aluminum: Aluminum is light, strong, and easily extruded into shapes required for window parts. Until recently, aluminum was the most common residential window framing material. Aluminum is generally very durable, especially if anodized or coated with a baked on enamel finish. One major disadvantage of aluminum is that it has a high thermal conductance. As a result, in cold conditions, an aluminum frame can easily become cold enough to condense moisture or frost on the inside surfaces of the window frame. This can result in the growth of mold or mildew, which can be difficult to control, is unhealthy and unsightly.

Wood: Wood is the traditional frame material of windows. Today, wood windows are considered high end due to their cost. Wood is susceptible to rot, and requires regular maintenance. With maintenance, however, wood windows can have a very long life. Cladding the exterior face of a wood frame with vinyl or aluminum creates a weather resistant surface, which reduces the maintenance required dramatically. Wood is attractive and is often favored for its appearance.

Vinyl: Vinyl frames are fairly new to the window market. However, they now account for more than half of all residential windows sold. Vinyl requires very little maintenance. Vinyl frames are very energy efficient, especially if they are insulated with foam. Vinyl cannot be painted or refinished.

There are several manufacturers of vinyl extrusions on the market today. Vinyl window manufacturers purchase these extrusions, then cut and assemble the windows to custom sizes. There are quality differences between the vinyl extrusions. Mainly, the quality difference has to do with the fillers utilized by the manufacturers.

Vinyl is Polyvinyl chloride (PVC). During the manufacturing of PVC for window extrusions, or any other vinyl product, fillers are used to increase volume and for mechanical reasons. A common filler used is calcium carbonate (CaCO3). CaCO3 is a common substance found around the world as rock. It is therefore inexpensive and readily utilized. CaCO3 forms a weak bond with PVC, and it tends to segregate when exposed to UV light. An example of this is the vinyl chairs that are often used for outdoor sitting. When you first purchase the vinyl chair, it is vibrant in color. After a couple of years in the sun, it will begin to flake and leave a residue on clothes when sat on, and the chair becomes drab. That residue is CaCO3. When it comes to windows, such residue and flaking would render the window unsightly. It is preferable that the vinyl fillers are more durable and form stronger bonds with PVC. For example, titanium dioxide (TiO2) is durable filler that is common in the window industry. A knowledgeable window professional can help provide information on the constituents of the vinyl utilized by specific window manufacturers.

Fiberglass: Fiberglass frames are also durable, strong, and have good insulating values. Fiberglass is stronger than vinyl, and therefore can make frames smaller than vinyl. Fiberglass windows, however, are more expensive than vinyl.

Wood Composites: Wood composite products utilize wood particles, such as sawdust, mixed with polymers, such as vinyl. These composites are very stable, and have thermal properties equal or greater than traditional wood. Since there are wood particles, the framing is still somewhat susceptible to water absorption and rot. Composites are often as expensive as traditional wood windows.