Renovation expert Mike Litchfield gives an overview of how different window-frame materials perform.
In the last few decades, there have been so many improvements in insulated glass that the R-value of the glazing generally exceeds that of the frames. In other words, windows with a larger percentage of glass (and a smaller percentage of frame) are better energy performers. In response, window makers are hustling to make window frames less conductive (of heat and cold), more airtight, and more durable. To do so, they have developed frames with a wide range of core materials, cladding, finishes, and in some cases insulation.
The chart below will give you an overview of how different frame materials perform, but to be honest, the best way to select a window is to choose a frame style that fits your house, calculate the energy performance your window must deliver (hence, the type of glazing, etc.), and then talk to builders and building-supply staffers about which manufacturers they favor. Try out windows as well, opening and shutting display models to see how tightly they fit, how smoothly they operate, and how sturdy they feel. Look especially closely at frame corners, glazing seals, and weatherstripping gaskets, for that’s where windows fail first. And when scrutinizing window cross sections, try to envision cold air encountering that frame: Is there a thermal break that will slow or prevent cold air from chilling the frame and causing conductive heat loss?
Lastly, “you get what you pay for” is especially true when buying windows. Even frames fabricated from less expensive materials, such as vinyl, offer options such as chambers filled with foam insulation that raise performance—and cost.
Many of the terms used to describe doors are also used for windows. Window frames consist of jambs—side jambs and a head jamb—and a sloped sill. Window frames also have stops to guide sash movement and provide a seal. Window sashes, like doors, have horizontal rails and vertical stiles. And casing is applied, inside and out, to limit air infiltration and impart a trim, finished look to the perimeter of windows. Lastly, many styles have terms that describe particulars of construction, such as the muntins and meeting rails of double-hung windows.
Excerpted from Renovation, 5th Edition (The Taunton Press, 2019) by Michael Litchfield and Chip Harley