Everything You Need to Know About Window Materials

We're raising the curtain on windows, answering your toughest questions: Which window material is best? Should I prioritize cost or quality? What do those rating stickers even mean?

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When you're house-hunting, a wall of windows signals lots of natural light and aesthetic appeal. But when you're renovating, all that glass can equal major expense and lots of decision-making headaches. Not only are there style considerations to think through, but there are practical choices, too, related to cost, insulation, frame material, and more. It's easy to feel overwhelmed.

The first thing to know: You will generally pay more for a window that has greater insulating properties and is better equipped to withstand the elements. As tempting as it is to scrimp, windows aren't the place to be overly budget-conscious. In the long run, it's usually most cost-effective to install the best window you can afford.

Nearly every window seals out wind when the temperature is comfortable. But when the mercury drops below freezing, many types of weather stripping shrink and stiffen, becoming brittle and eventually cracking. This compromises the window's seal. Only the highest-quality windows perform well when temperatures plunge below zero.

If you're starting a renovation or building a home, select and order your windows as early as possible. The least expensive windows come in standard sizes, which you may be able to simply pick up at a home center or supply store. But custom windows cost more and may take several weeks to arrive. If the window is delivered with a flaw, is damaged in shipment, or is the wrong size, you'll have to reorder. That's why wiggle room is critical.

We'll walk you through some of the features to consider when purchasing windows, but keep in mind: It's always worth consulting a knowledgeable salesperson at a home center or window supply store to help you choose the best product for your needs.

What Are Windows Made of?

Window frames can be made of vinyl, fiberglass, metal, or wood (which may be clad with aluminum or vinyl on the exterior portions). Higher-quality (and generally costlier) windows have better weather stripping to keep air from filtering in around the sashes. The window glass may be single-, double-, or even triple-paned, and it may be treated with a coating that keeps warmth inside during the winter and outside during the summer. We'll break down each of these features in more detail below.

How to Decipher Window Ratings

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Most windows come with a rating sticker that includes performance scores for at least some of the following factors:

R-value: This measures the window's ability to prevent heat transfer—how it keeps uncomfortable temperatures outside and comfortable temperatures inside. The higher the R-value, the better.

U-value (or U-factor): Essentially the inverse of the R-value, the U-value measures the tendency to transfer heat and tells you how well the window insulates. The lower the number—which typically ranges from .20 to 1.20—the better.

Solar gain (also called solar heat gain coefficient, or SHGC): This rating indicates how much heat the window allows in when the sun is shining. Solar gain is a good thing when the weather is cold, but it can raise air-conditioning costs during the summer. The higher the number, the greater the heat gain. This number will fall somewhere between 0 and 1.

Wind resistance (or air leakage): Measured in cubic feet per minute (CFM), this number tells you how much heat comes in and goes out through the natural gaps in the window's frame. There should be two numbers: one for 70° F and one for 0° F. The lower the numbers, the better the seal.

Visible transmittance: If you care about natural light, this is your number to consider. Ranging from 0 to 10, the visible transmittance rating signals how much light filters through the window, with 0 indicating opacity and 1 meaning maximum natural light. (This number takes into account the glass as well as non-transparent features, like frames and grids.)

Condensation resistance: Loathe foggy windows? This rating, which ranges from 0 to 100, measures how well the glass resists condensation on the inside surface (which can happen when it's cold outside but humid inside). The higher the number, the better the resistance.

The Right Window for Your Region

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In northern climates, sealing out cold is the primary concern, while in southern areas, the focus is on keeping out the heat. This map gives a general idea of the types of windows appropriate for each region; consult local window dealers for more specific recommendations. Again, U-factor refers to the rate of heat transfer, and solar gain signals the amount of heat that penetrates the glass (see above for more information on these ratings).

7 Types of Windows to Consider

Vinyl Windows

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Vinyl windows are usually the least expensive choice and are suitable for many applications. In lower-quality models, the weather stripping (which is typically fuzzy) is not very durable, and some of the plastic parts may break, especially when the window is tilted out for cleaning. Vinyl contracts and expands with changing temperatures, reducing its ability to seal. It can also warp if exposed to very hot sunlight. Vinyl can be painted (it helps to apply alcohol-based primer first), but the paint may peel and need to be reapplied after a few years.

Wood Windows

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Wood generally costs more than vinyl, and it periodically needs to be sealed with paint or finish to prevent rotting and sun damage. However, wood has natural insulating properties, and most people prefer the way it looks. Some wood windows are made with stain-quality material, but those that have obvious joints will not look good if you stain them—plan to paint these instead.

Clad Windows

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To make a wood window more durable, many manufacturers apply a cladding of aluminum, vinyl, or fiberglass to the exterior portions only. Aluminum cladding can be painted, as long as you apply a primer first. In most cases, tinted vinyl and fiberglass can be painted with no problem, but paint may have trouble sticking to white vinyl. You can also buy windows with hard-baked paint finishes.

Fiberglass Windows

Some manufacturers make fiberglass windows, in addition to the standard offerings mentioned above. Fiberglass is stronger than vinyl, less prone to contracting and expanding, and less likely to warp. It needs to be protected by paint, which manufacturers anticipate by applying a hard finish at the factory.

Double-Hung Windows

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The double-hung window is the most common type, thanks to its versatility and ease of operation. It has a number of specialized parts that make it unique: First, the exterior sill is slightly sloped so water can run off. Second, the interior stool (often called the inside sill) is typically just wide enough for a small plant; if it were wider, people would bump into it. Stop moldings and parting stops are precisely aligned to ensure the window seals, while still allowing sashes to slide up and down easily. The weight-and-pulley system shown above is typical of older wood windows; newer windows use friction or springs to keep the sashes in place when they're raised.

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Tilt-Out Windows

Many windows tilt out for easy cleaning from the inside. Beware, however, of cheap windows with this feature; the hardware could break as you tilt them out and snap them back in.

Storm Windows

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A well-made and tightly installed storm window can do wonders for an old window, boosting its insulation efficiency by trapping several inches of air between the window and the storm window.

Other Window Features to Consider

Flanged and Block Frames

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A flanged window attaches to the house with a flange—an angled, fin-like strip—that is nailed or screwed to the exterior sheathing. A block-framed window has no flange and slides into an opening. This is the right choice when you want to install a replacement window into an existing frame.

Glazed Panes

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Single-glazed windows, with a single pane of glass in each sash, are the most affordable type, but they allow lots of heat transfer, making for hefty heating and air-conditioning costs. In older single-glazed windows, glazing compound (putty) on the outside holds in the panes. For newer windows, snap-in molding pieces take the place of putty.

A double-glazed pane, also called insulating glass (IG) or thermal glass, dramatically increases a window's energy efficiency. The two panes create an insulating air space between the two sheets of glass. The larger the air space, the greater the insulating power.

You can increase a double-pane window's insulation efficiency by ordering it with argon or krypton gas between the panes instead of air. Note that gas-filling usually costs more and can prolong delivery time. The gas will leach out over time, but very slowly; after 20 years, the pane should still have 90 percent of its original gas.

Triple-glazed windows, featuring three panes and two air spaces, are also available. These are not common, because the extra insulation usually isn't considered worth the significant increase in cost.

Removable Grids

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A removable grid hangs over a single pane of glass to mimic the look of an old-fashioned window with muntins and several small panes. The grid lifts off for easy cleaning.

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