As we rolled past a security gate, I was informed that the 40-acre complex we were entering was a former Soviet tank factory. After weaving through a maze of austere industrial structures, we came upon a small building that looked out of place with its bright yellow stucco exterior and its beautiful wood windows. Makrowin, the company located there, manufactures what we in this country call European windows, or "tilt-and-turn" windows (because most of them open by either tilting in at the top or swinging in like a door). This facility was the first stop on a recent trip through areas of Europe where I got to see what goes into fabricating these extraordinary products known not only for their furniture-like aesthetic quality but for exceptional operation and performance that are hard to equal anywhere.
Where it began
Although European windows are some of the most thermally efficient windows manufactured in the world, their development was spurred by concerns other than energy efficiency. During the last couple of decades, as homes in Europe became more airtight and more thermally efficient, double-glazed windows—widely used in Europe at the time—came under scrutiny for health reasons. Condensation consistently developed on the glass, which contributed to mold growth. This, coupled with inadequate mechanical ventilation, produced major problems with interior air quality in homes.
The glazing industry responded by creating triple-glazed insulating glass packages with improved U-values. The heavier glazing units then led window manufacturers to produce thicker laminated-wood frames. Triple glazing and sturdier frames propelled the industry to a new level of product advancement. At the same time that window technology was exploding, the Passive House Standard, a new highly advanced approach to building, was taking hold in Europe. These two paths soon crossed and are now inextricably linked.
With health concerns solved, the industry turned to improving the energy efficiency of the windows to meet the stricter building standards coming online. New ways of thermally breaking the window frames were developed, prompting hardware companies to scrutinize the thermal properties of the operating mechanisms. Manufacturers of all of the windows' components adopted an "all in" philosophy, resulting in windows of superior quality and very high performance.
Made to order
As an architect who designs low-energy, airtight homes—striving to meet Passive House standards on many of them—I have difficulty finding the right windows domestically, so I usually opt for European windows, specifically the triple-glazed units. The reason is simple: The flexibility in their production allows me to procure the appropriate windows for any project.
European windows are not subject to the standard sizing and typical conventions—such as predetermined levels of quality—that govern most windows made in the U.S. Every European window is built to order, created from scratch within a matrix of configuration and component options. So instead of designing a project around a set of window parameters, I can design the project first and then order windows that meet its exact requirements, including size and color as well as performance. The concept we have in the U.S. of "customizing" window design simply does not exist in Europe.
The glass comes first
The heart of every window—regardless of where it's made—is the glazing, or the insulated glass unit (IGU), that's installed in the frame. IGUs for European windows are made in a separate facility by a company different from the one that assembles the final product. Glass comes into the IGU factory in huge sheets (3 meters by 8 meters) in whatever glass type is required, such as low-E coated or laminated. The sheets are laid flat and are cut to the proper IGU size on a CNC machine. While it's cutting, the CNC machine also prepares the edges of the glass panels for installation by grinding any coatings off so they will accept a sealant.
While the glass is being meticulously cleaned, a worker prepares the welded metal spacers that separate the layers of glass. Next, the glass moves to the gas-filling station. Argon gas—so critical to the performance of these windows—is not injected into the frames. Instead, the sheets of glass and the spacers are aligned in a loose assembly (close but not touching) and placed into a chamber from which the air is subsequently evacuated and replaced with argon. The glass and spacer sandwich is then compressed together, sealing the argon between the sheets. After the argon is evacuated from the chamber and replaced with air, the argon-filled IGU emerges. The edges are given a final seal, and the IGU is packaged with the rest of the order and shipped to the window manufacturer.
Although European windows are available in a variety of frame materials, wood-frame windows have traditionally been the most popular choice. Recently, however, wood-frame windows that are clad with aluminum have been gaining in popularity. Clad or not, the wood frames themselves are constructed along the same assembly line. They are made of laminated wood that comes to the factory in 18-foot lengths and is roughly 3 1/2 inches square. All the wood used by Makrowin is sourced from nearby forests (within about 125 miles of the factory) that are managed under strict regulations.
The laminated wood frame adds strength and durability to the windows, which is especially critical when they reach lengths up to 17 feet. Each interior laminated section of the frame is finger-jointed, which may make some American craftsmen cringe. But I was told that most builders in Europe prefer the finger-jointed wood and usually specify it as a component of the windows they order. Because of high-tech cutting methods and adhesives, finger-jointed wood is stronger and more stable than solid wood. For aesthetic reasons, the outer laminate of the frame—the piece that is visible as the interior finish of the window—is a solid rather than finger-jointed piece of wood.
Compared with solid wood, the laminated frames offer superior holding and pull-out strength for fasteners, ensuring durable connections for all the operating hardware. The extra strength also allows for fewer hinges, even with heavy, triple-glazed IGUs. And if a project calls for elevated U-values in the frame, manufacturers can substitute layers of cork for some of the wood laminations to provide a continuous thermal break around the perimeter of the frame.
A human touch among the machines
Rough-cut blanks enter a system of saws and shapers that precisely cut the frames to length and create glue joints at each end. Mortises and pilot holes for hardware are also cut at this point. Though companies fabricate these window frames using some of the most high-tech equipment available, it was interesting to learn that each frame receives more than an hour of hand-sanding. I was skeptical about this until I watched as an employee with a collection of specific sanding blocks orchestrated a personal stamp of perfection to each unit she handled. In a shop filled with high-tech shapers, drills, and saws, the final finish is left to human hands. Thinking back on all the times I've admired the quality of these windows, I now realize why they always look so good.
After an initial sanding, each wood frame goes through an elaborate finishing process that includes a bath in organic-growth repellent and coats of sealant, with light sanding between. Before final finishing, a special sealant is applied to each corner joint. That thin film bridges the two sides to protect the joint and the finish should any slight movement occur.
The frames are then sent into the finishing room where they are air cleaned and finished to the specifications of the order. For windows with an operable sash and complimentary glazing stop, the pieces are hung in tandem and finished in unison to ensure that the finish is an exact match when they are placed adjacent to one another in the final assembly. The humidity in the finishing room is closely maintained at 70%—the optimal level for curing set by the finish manufacturer—which lets the finish "relax" completely, resulting in an extremely smooth surface that's free of the kind of texture that spray finishes often leave.
Hardware installation occurs after finishing to ensure that all surfaces on the frames are finished before the windows are assembled. The elaborate hardware for these windows is installed by hand, with the frames and sashes resting on a special padded table. The operation hardware, hinges, and locks are installed via pilot holes that had been drilled earlier to ensure their exact alignment. At this phase, the window units also receive weatherstripping. The sashes are then married to the IGU that was made especially for that unit. The IGUs are set in a glazing bead, and the glazing stops are applied.
If a window is to be clad in aluminum, it's at this stage that the pre-manufactured cladding is installed onto the wood frame. The cladding is produced at a separate facility and is welded and pre-finished when it arrives at the factory. We weren't able to see the aluminum cladding being produced, though, and were told that the process is a tightly guarded secret. The welds on corners of these frames are completely invisible, so I can't blame the maker for keeping the process under wraps.
After the cladding is installed, the finished window and door units are grouped according to project and are wrapped and packaged together to await departure from the factory and delivery to the jobsite. The typical lead time for delivery to the U.S. is 11 to 12 weeks or three months, which is about 30% longer than what you can typically expect for a high-end custom order from a domestic manufacturer. That time frame includes the usual total fabrication time of about eight weeks, with another three to four weeks allowed for transfer and delivery. Orders for the U.S. usually have priority, so windows destined for Europe typically have the same three-month delivery schedule, even without the overseas shipping.
Limitations & expectations
After the factory tour, I sat down with the owners of the window company to ask them some tough questions. I started with the upper limits for the size of these windows. As mentioned earlier, the rough stock for the laminated frames comes in lengths of around 18 feet, so the longest dimension possible in a fixed triple-glazed window is about 17 feet.
As for operable windows, they told me that maintaining an aspect ratio of 1:2 (horizontal:vertical) is a good rule of thumb. That means, for example, that a 5-foot-wide, 10-foot-tall operable window can readily be produced.
To answer my questions about the durability and longevity of the wood frames and the hardware, the company's owners showed me examples of wood windows in a nearby village that are still in fine operating condition after more than a century of use.
Obviously these old windows don't offer the same energy performance as the modern ones do, but that's still a respectable achievement. As for the double-glazed windows from the last 50 years that we mentioned earlier, most are still operating and performing as designed.
The window components typically carry a 10-year warranty. For windows currently being manufactured, the experts I spoke with believe that of the four basic components—IGU (glazing), wood frame, hardware, and aluminum cladding—the IGU is the weakest.
But, that said, by law an IGU can't lose more than 1% of its argon fill per year. The glazing manufacturer, using all third-party testing, reports less than 0.01% loss of argon per year, which is 100 times better than what is required. And because of the component construction, if the IGU does fail, it can easily be replaced without the entire window being removed.
A sea of options
While touring window manufacturers in Europe, I attended a huge trade show where I saw an incredible array of options for these high-tech windows.
One popular choice is a PVC frame. Its performance is very similar to that of its wood counterparts, and depending on the size of the unit, it can be reinforced with steel—though one of the PVC reps at the show told me that his company is moving toward using recycled aluminum for reinforcement in the near future.
Another option is an aluminum-frame window thermally broken with a foam-filled plastic channel that separates the interior and exterior frames. The performance of these windows is supposedly equal to wood-frame windows. Because the frames are hand-welded, metal-frame windows tend to be more expensive.
There are more options than I can list, but here are a few other notable ones. Integrated solar shades, important for energy-efficient homes, are available in a wide variety of configurations. Another useful option reverses the typical turn-then-tilt operation to tilt-before-turn. Most windows are also available with accessible hardware and child-safe hardware for either manual or motorized operation. Motorized hardware can be integrated with a home's energy system to operate in accordance with changes in interior or exterior climate conditions. All windows and doors have options to meet Europe's stringent security requirements. To meet demands for indoor air quality in the super-tight homes in which these windows will be installed, small heat recovery ventilators can even be built into the window units. Finally, at additional cost, the windows can be made with high levels of resistance to fire, impact, and sound transmission.
The options you can order for these windows seem limitless—and if you have a special requirement, chances are the manufacturer will find a way to accommodate it.
The Crystal Ball
What does the future hold for window technology? The experts told me that moving to a quad-pane window (four layers of glass) seems to be next, although most believe that improvements in "hard coatings" on the glazing will produce the performance of quad glazing in the current triple-glazing configuration. Except for historical applications, aluminum-clad windows will eventually make the exposed-wood-frame window obsolete. Frame insulation and performance is always improving, and client demand for better performance in VLT (visible light transmittance) and SHGC (solar heat gain coefficient) will maintain pressure on the IGU manufacturers to improve their products as well.
The Bottom Line
It's impossible to give an exact cost of these windows and doors because of the complex matrix of options available. Manufacturers told me to use $75 to $125 per square foot for estimating purposes. But keep in mind that because the IGU is the least expensive component of the window, bigger windows have a cheaper per- square-foot price than smaller windows. Some may look at this advanced technology and say that it's too expensive. But if you understand that windows and doors are the lowest-performing component in any wall system, doesn't it make sense to choose the best-performing windows you can get?
Steve Baczek of Reading, Mass., is an architect specializing in energy-efficient design and certified passive homes,stevenbaczekarchitect.com.