Windows 101: Window Frame Materials and Glass Options

In our previous blog post we reviewed many of the most common window types, but what about the options for window frames and glass? We will delve into some of those details here.

Window Frames

Windows frames come in a variety of materials. They can be fabricated from a single material or they might have different materials on the interior and exterior. As you might expect, there are different price points associated with the various options, and even from manufacturer to manufacturer there can be differences in both price and quality. Unfortunately it’s not possible to list the material options in order from lowest to highest price, but generally vinyl will be the most budget-friendly option across the board, and steel will almost always be significantly more expensive than everything else. For all the material options in between, you would need to have a conversation with a contractor or window rep to receive accurate pricing.

Vinyl

Vinyl is a very common residential window frame material and great for situations where cost is the key priority. Additional benefits are that vinyl requires minimal maintenance and is typically lightweight and easy to install. On the other hand, color options are limited, and prolonged exposure to UV often causes color fading or yellowing over time. Vinyl windows also often have bulkier frames than other materials, which is not always desired. It can also be difficult to recycle the product at the end of its life cycle, which creates additional landfill waste.

 

 

Clad/Composite

Clad windows, also referred to as composite windows, typically have a painted or stained wood face on the interior, and then the exterior face is a more durable material such as aluminum or fiberglass. The clad exterior protects the window frame from weathering and provides a maintenance-free finish while still having a wood interior that looks more high-end. The downside of clad windows is that they can be difficult to repair if the cladding material gets damaged, and if the wood behind the clad exterior is deteriorating sometimes it’s not visible until the damage is advanced. However, a lot of people choose to install clad windows because they provide a high-end look while generally being low maintenance.

Fiberglass

Fiberglass windows are strong, attractive, and require minimal maintenance. Fiberglass performs very well as an insulating material and can withstand large temperature swings without any expansion or contraction issues like other materials. Similar to vinyl, there may be limited color choices available, but some manufacturers do offer a different color on the exterior and interior to achieve a more high-end look. Fiberglass is typically more expensive than vinyl, but it is a more durable material and should last longer, with a longer warranty as well.

Wood

Wood is a traditional window frame material with a timeless look and feel, although most windows don’t have exposed wood on the exterior these days unless they are historic. One of the reasons wood has been such a popular choice for windows is that it readily accepts any paint or stained finish and can work with many different architectural styles. Wood is beautiful and provides good insulative properties, but it is a material that requires a lot of care to stay in premium shape. Wood is susceptible to bugs, weathering, and rotting if not maintained properly, and it will expand and contract with the seasons and humidity. Wood windows will need to be refinished every five to ten years, and they are often more expensive than many other materials.

Aluminum

Aluminum windows are considered to be relatively strong and lightweight with limited maintenance needed. They tend to be more common in modern homes where large openings with narrow frames are a key element in the design. Aluminum is very durable and lends itself to a variety of shapes and sizes that may not be as readily available or possible in other materials. They are, however, very poor insulators and can result in significant heat loss between the interior and exterior of the home. Newer aluminum windows will often include a thermal break to help reduce the heat transfer, but if thermal performance is a primary consideration then aluminum may not be the best option for your home.

UPVC

UPVC is a relative newcomer to the US market, but it’s been available in Europe for a long time. UPVC is a hard, recyclable plastic that does not contain phthalates or BPA. It is not the same as PVC, despite the similar names. For windows, UPVC is similar to vinyl in that it’s reasonably inexpensive, provides good thermal performance, and is considered a maintenance-free solution. However, UPVC is more resistant to fading and discoloration than vinyl. For color options, UPVC window frames can be coated with a film so it looks like metal, wood, and an almost infinite number of colors. The frames of UPVC windows tend to be bulky, which may be a downside for homeowners that want a more minimal window. Also, if the decorative color/pattern coating on the UPVC gets damaged it is difficult to repair.

Steel

Steel windows are, without a doubt, a premium choice for window frames. They are incredibly beautiful, and stylistically steel windows can work in both traditional and modern buildings. Steel is also exceedingly strong, which means windows can be larger and hold bigger panes of glass, the mullions are thinner, and the durability of the steel means windows last longer than almost any other material. Unfortunately, the price point of steel windows means only those with the deepest pockets are able to afford them.

Glass Options for Windows

While it may seem surprising, the reality is there are almost as many choices for window glazing as there are for window frame materials. From type of glass to number of panes to gas fillings, choosing the right glass for the right conditions is important.

Fun fact: most window manufacturers do not make their own glass. Instead, they almost all buy from a handful of glass manufacturers, such as Cardinal Glass Industries, Viracon, and Vitro Architectural Glass.

Types of Glass

Float glass is the most basic type of glass, and when it is cooled slowly it is called annealed glass. The process of annealing strengthens float glass so it doesn’t break as easily. Annealed glass is what is used to make windows.

Tempered Glass

Tempered glass is also called safety glass, and it is significantly stronger than annealed glass. Unlike float or annealed glass, which breaks into large shards, when tempered glass breaks it does so into small pieces that are less likely to significantly injure someone.

In windows, tempered glass must be used for large windows where any individual pane is greater than nine square feet, when the bottom edge of glazing is less than 18 inches above the floor, when the top edge of the glazing in greater than 36 inches above the floor, if they’re within 36 inches of a walking surface, if they’re installed near doors or other impact-prone locations, or wherever safety is a concern. For more detailed information about safety glass in windows, refer to Section 2406.4.3 of the International Building Code.

Tempered glass is more expensive than annealed glass, but it is still considered affordable.

Laminated Glass

Laminated glass is comprised of two or more layers of glass (usually tempered glass but sometimes only annealed) with a thin plastic layer between the panes. When laminated glass breaks, the pieces generally adhere to the plastic middle layer to avoid causing serious injury.

In residential windows, laminated glass is most often used in skylights, but it can also be used in very large windows and in hurricane-prone areas.

Hurricane/Impact-Resistant Glass

Hurricane/impact-resistant glass is sometimes called “safety glass on steroids,” and it is most commonly used in places like Florida, where hurricanes are a regular occurrence. While some locations allow homeowners to use storm shutters or hang plywood over windows, other jurisdictions may require the use of hurricane glass, especially for new construction. Hurricane glass is typically made with three layers of tempered glass and an interlayer between two of the layers, as indicated in this drawing from Pella.

Insulated Glass (IG)

Insulated glass (IG) consists of two or more panes with an air space between them. The air space, usually about half an inch, may be filled with an inert gas like argon or krypton to help improve the insulating factor. In an insulated glass unit, the glass panes can be annealed or tempered.

To further increase the thermal properties of an IG unit, a low emissivity coating (low E) is often also be applied to the inside of one of the panes of glass. Low E coatings reflect UV light rays, which in turn reduces the solar heat gain inside the house and decreases the load on a home’s mechanical system.

There are other types of glass as well, such as fire-rated glass, but that is used primarily in commercial buildings and for this feature we are focusing more residential windows.

Choosing the Right Number of Glass Panes

Single-pane windows were the universal standard for windows until the mid to late Twentieth Century, when double-pane windows became the residential standard. With the improved thermal performance achieved by using insulated glass, the energy efficiency of homes was significantly upgraded. Today double-paned windows are still the go-to for homes and handily meet the energy-efficiency needs in most climates.

In extreme climates, making the jump to triple-pane windows may make sense to achieve a more rigorous level of energy efficiency. Alternately, if the outside environment is very loud, then triple-paned windows can make sense to provide enhanced sound protection. However, there is a price difference between double and triple paned windows, so if you are considering triple-paned windows be sure the additional cost makes sense.

In climates where both double or triple-pane windows are viable options, it would be worth having an energy model run to calculate the expected performance and energy savings. Sometimes only a portion of the windows on the house need to be triple-pane, and the balance of windows can remain double-pane. If you won’t be bothered by the slightly different look of the double vs. triple pane window frames, combining window types might be a great opportunity to optimize performance and save some money.

Balancing Budget with Performance

As we’ve discussed in these last two blog posts, there are many options pertaining to style and performance available on the market that hit many price points and achieve different aesthetics. During the planning phase, talk through your favorite options with your architect and contractor. They will be able to help you understand the pros and cons of the different options. They will also have connections to local window reps who can provide detailed information and answer all of your questions about their products.

Look for our next post to cover colors, grilles, and other design details.