HomeLink Magazine Winter 2015: European Windows and Doors

Glass Envy

The Case for European High Performance Windows & Doors 

By: Florian Speier, Zola Windows

European high performance windows and doors allow a homeowner to lower utility costs, increase comfort, and capture the Yampa Valley’s natural beauty. 

European windows are significantly more energy efficient and durable than their American counterparts. It is not uncommon for a European window and frame to last fifty or sixty years without requiring major maintenance. This is almost unheard of with American windows.

The energy efficiency of a window is determined by its R-value and/or its U-value. The R-value measures the capacity of a material to resist heat flow.  The higher the R-value, the greater its insulating power. The U-value is the R-value’s inverse. The U-value measures the capacity of a material to resist heat transmission. The lower the U-value, the greater its insulating properties. A simple way to think of R-value and U-value is R-value measures how well a window prevents the cold from entering a home, and U-value measures how well a window prevents heat from escaping a house. American manufactured energy efficient windows, typically have an R-value of 2 – 3 and a U-value of .25 – 1.25. A comparable European manufactured window will have an R-value of 10 – 11 and a U-value of .09 – .12 

Tilt & Turn vs. Slide

European windows achieve their vastly superior energy efficiency in numerous ways.  American window manufacturers commonly make windows that slide open. As a basic rule, European window manufactures do not produce slide windows. Instead, the main operational window mechanics is a tilt and turn model. The tilt and turn window can open on its side hinges, much like an entry door, or tilt inwards approximately fifteen degrees to allow for ventilation. When a window opens along a slide, it is almost impossible to create an airtight seal. With a tilt and turn opening mechanism, an inside awning and casement within the unit creates a virtual airtight seal. 


European windows also employ different frame design and technology than domestic windows, which significantly improves their energy performance. It is not uncommon for European window manufacturers to layer an insulating material into the window frame before it is cut. Layering insulation into the window frame at this point in the manufacturing process allows a full thermal break which penetrates through the entire frame. Some of the European window manufactures use Purenit™, a patented German material of recycled polyurethane composite. Purenit™ has two times the R-value of wood, so every inch of Purenit™ is equal to two inches of wood in terms of insulation value. Therefore when Purenit™ is layered inside a window frame, the window will insulate better than almost any domestic manufactured frame and creates a full thermal break with the outside elements for even greater performance and comfort. 


European window manufacturers are opting for thicker and thicker panes of glass and increasing the space between each pane. The thicker glass and greater space between panes increases the performance of the window by providing better insulation and Solar Heat Gain Coefficient (SHGC). SHGC measures how much of the sun’s energy striking the window is transmitted through the window as heat. Windows with a high SHGC allow for passive solar heating which is ideal for those cold, clear Steamboat winter days. The space between glass panes in European windows is wider, which allows for an extra performance boost between ten and forty degrees F. Any person planning to purchase windows for a project located five thousand feet from sea level or higher needs to examine and question the pressurization system employed by the window manufacturer to ensure the performance and life expectancy of the window is not compromised. Different European window manufacturers use different methods to address the pressurization issue. Educating yourself on the methods used by manufactures to minimize seal failure, gas loss, and window breakage for projects at high altitudes, will help protect your investment in your European windows and doors.

European window manufacturers employ a different type of glazing than their American counterparts. In Europe the vast market for solar panels has allowed European glass manufacturers to realize economies of scale to create extremely high performance glass at prices not achievable in the United States. European glass has a lower iron content than its American counterpart, which translates into higher clarity with no color shift. When American windows employ thicker glass panes, the increased iron in the glass causes a color shift in the light passing through the window. If an American window with thicker glass panes were installed in a bathroom with white tile, the sunlight passing through the window would cause the tiles to look green. European windows would not distort the tile’s color. The superior European glass also have a low E, or emissivity, coating applied to the raw glass before it is manufactured into a window. The low E-coating allows for higher solar heat gain and higher visible transmittance, or VT. VT is the amount of visual light that comes through the window. The higher solar heat gain, and visible transmittance in European windows allows them to provide a level of comfort rarely achievable with American windows. With European windows, a homeowner does not have to choose between energy efficiency and obscured views.

Glass Panel Exterior Doors

What holds true for the difference between American and European windows is equally applicable for doors such as large lift and slide and accordion doors. European doors are manufactured for optimal heat retention and energy efficiency. These doors create an airtight seal which is virtually unmatched by any domestic door manufacturer, as they often employ a triple to quadruple compression seal. This results in approximately ten times the airtightness of standard American doors. The multipoint locking mechanisms make the doors virtually impregnable to burglars, except through glass breakage. A European sliding door lifts and slides along an embedded track, which can create a moving glass wall at sizes and performance currently unavailable on the domestic market. Combined with the glass and framing technology of European windows, homeowners with a European manufactured door will cause their neighbors to experience door envy.


A homeowner deciding to go with European windows and doors, needs to build in extra lead time to allow the product to be manufactured in Europe and shipped to the United States. Depending on where the windows are manufactured in Europe and the type of window being purchased, European windows and doors should be ordered twelve to fourteen weeks before they are scheduled to be installed for a project in the Yampa Valley. Given that almost all European manufactured windows are high performance windows, they tend to be more expensive than traditional American made windows/doors. Further, during the installation process, it is helpful to have an individual who is familiar with installing European windows and doors.  A high performance window/door not installed properly, can have its performance potential significantly decreased. Like American windows and doors, not all European window manufacturers are the same, and not all European window manufactures have obtained the necessary certifications to sell their products in the United States. It is important to double check the National Fenestration Rating Council’s ratings of any window manufacturer to ensure compliance with local building codes. 

North Americans are becoming more conscious of the importance of energy conservation. Forty percent of all energy consumption in the United States is attributed to buildings. In an average day, a person’s residence is their greatest carbon footprint.  Homes and businesses using European windows and doors experience far superior heat retention resulting in a significant decrease in energy consumption and reduced energy bills, compared to homes or businesses with domestic windows and doors. In addition, European windows create greater comfort for the building’s occupants.