Robover’s FAQ section answers many frequently asked questions

It is a source of relevant information on the high-quality products at your disposal. Consulting the FAQ will give you information on a series of subjects related to your questions.

If you have additional questions, please contact us. We will answer as soon as possible, with the same pleasure and the same courtesy that we showcase every day.



Why do we use argon in the manufacture of insulating glass?

Argon is one of the most commonly used gasses in the manufacture of insulating glass units. It is a better insulator than air because its thermal conductivity is 1.3 times lower. Argon is also denser, which limits the movement of air in the insulating glass unit and thus improves the thermal performance.

Is argon dangerous?

Argon is a colorless, tasteless and odourless inert gas. It makes up almost 1% of the atmosphere of the earth. If the window glass breaks, there is no health risk.


What is the difference between the Shading Coefficient (SC) and the Solar Heat Gain Coefficient (SHGC)?

The Shading Coefficient (SC) is the ratio of solar gain to that passing through a clear glasspane 3.17 mm (1/8 inch) thick (which has a factor of 1.0).

The Solar Heat Gain Coefficient (SHGC) is lower for the same product.

For a glass pane 3.17 mm (1/8 inch) thick, the Solar Heat Gain Coefficient is equal to 86% of the Shading Coefficient. In both cases, a lower number indicates lower solar gain.


Why does condensation form on the exterior surface of insulating glass units?

Condensation on the exterior surface of insulating glass units is a normal phenomenon that may occur under certain atmospheric conditions. It is caused by heat exchanged between the glass and the surrounding environment. The quality of the glass unit is not a factor. Under certain conditions (clear night sky, light wind, high humidity), the temperature of an insulating unit’s exterior glass can drop enough that the humidity in the air condenses on its surface. These conditions may occur several times throughout the year. As soon as the exterior glass heats up, usually early in the morning, the condensation disappears.

Under equivalent conditions, less efficient insulating glass units allow more heat to enter than highly energy efficient units. This heat warms up the exterior glass, making it less likely that condensation will form. Accordingly, condensation is less likely to occur on less efficient insulating glass units. However, highly energy efficient units help save energy, reduce condensation on the interior glass, reduce the risk of mold on the interior edges of windows, and enhance the comfort of your home year round.

Glass marks

Why do marks sometimes appear on the glass surface?

Window fabrication and installation practices utilize many techniques to process, store, handle and install the glass. These means may include, but are not limited to, the use of separator pads, conveyors, brushes and suction cups. While the use of these devices does not leave a visible residue on the glass surface, they do change the surface condition of the glass, which could change the visual appearance under certain conditions.

When water would bead up on the glass surface from condensation, rain, or other raisons, different water beading patterns can create an outline with distinct lines of demarcation, which can take the shape of the device that had previously contacted the glass surface in this area.
While this appearance would be noticeable under certain conditions, it does not affect the functionality, performance, or longevity of the glass. It is possible that this condition will dissipate over time with normal exposure to the elements and regular glass cleaning.

Infrared Radiation

What is the difference between long-wave and short wave infrared radiation?

Short-wave infrared radiation comes directly from the sun, but is not felt as heat. This type of radiation converts to heat when it reaches a certain mass.
Long-wave infrared radiation is emitted by any mass that has absorbed heat.


Am I going to notice a difference in light quality between my clear windows and my new Low-E windows?

You will notice a reduction in light intensity compared to your former windows. However, what most people notice is the increase in comfort.

Do all Low-E glasses look the same?

Low-E glasses are not alike all. The various components of the coating, its thickness, the number of layers and the manufacturing process have an influence on the color of the finished product and its characteristics.

Do Low-E coatings work as well at night when the sun isn’t shining?

Low-E coatings work 24 hours a day. In the winter, they reflect the heat (long-wave infrared energy) back into the interior, day and night. Low-E coatings do not differentiate between furnace heat and heat created by solar energy, as they are both absorbed and re-radiated back to the source side.

Can tinted glass be used in combination with Low-E glass?

Yes, it can. Sealed units can be made with tinted glass as long as Low-E glass is used on the interior pane. However, as mentioned in the section on types of glass, all windows should have glass that is the same thickness.

How does Low-E glass reflect the heat?

The three heat transmission modes are conduction, convection and radiation. The Low-E glass has an impact on the heat transfer by radiation (heat), much like a mirror reflects light.

Is it more difficult to clean windows that use Low-E glass?

At Robover, the coating is always on the inside surface of the sealed unit. The exposed surfaces are made of regular uncoated glass that can be cleaned like ordinary glass.

Is there a difference in appearance between a window with a Low-E glass and a window with clear glass?

There is a slight difference in appearance, but it is very hard to see. If you put Low-E coated glass beside clear glass, you might notice a slight difference.

Will Low-E glass work in all climates?

Low-E coated glass can work in all climates. Low-E coatings reduce heat loss from the interior through windows, thus reducing the energy used to heat buildings and associated heating costs. And Low-E coatings also offer solar control that reduces heat gain due to both the transmitted solar energy and conducted heat caused by indoor – outdoor temperature difference. This reduces cooling loads and consequently the energy and costs associates with cooling the building.

Tempered glass

How do you know if glass is tempered?

Every piece of tempered glass is permanently marked (for example laser or acid etched, sandblasted) to signify it is tempered.

Where is the tempering stamp located on the glass?

Tempering stamp is located in one of the corners of every piece of tempered glass.

On which surface of an IG unit is the tempering stamp usually located?

There is no standard or regulation specifying the location of the tempering stamp.

What are the effects of heat-treating glass?

To make tempered glass, the glass is reheated to just below the melting point and then quickly air-cooled, which cause optical distortion to some degree. During the heating process, the glass will sag slightly between the carrier rollers in the furnace. Because of its fluidity at higher temperatures, glass also is inherently susceptible to roller wave, bow and warp while it is being heat-treated. Although glass thickness and size can affect the amount of distortion, the effect of distortion cannot be eliminated and is not considered a defect in the manufacture of heat-strengthened or fully tempered glass.

Thermal breakage

What causes thermal breakage?

Breakage by thermal shock occurs when stress is generated by a difference in temperature between two points within a glass pane. This difference can, for example, be between one point of an IG unit exposed to the sun and another in a shaded area.

Under the effect of the sun, the IG unit heats up as it absorbs energy. If part of the IG unit remains cold, it keeps the hotter part from expanding freely, thus generating compressive and tensile stress respectively in the hot and cold points of the IG unit. Because glass is less resistant to traction than to compression, the generated tensile stress may exceed the tensile strength of the glass and cause breakage. This is what is known as thermal breakage.

The origin of the break appears at the edge of the window (in the coldest area of the frame) and is characterized by a perpendicular (90°) fracture at the edge on both sides of the glass. The fracture can be monofilament or multifilament.

What are the risk factors?

The risk of thermal breakage may be related to the following factors:

Climate conditions : The difference in temperature within an IG unit depends directly on the intensity of the solar radiation that reaches it (depending on the orientation of the IG unit, the time of day, and the season) and the maximum difference in temperature between day and night. IG units facing north pose little risk of thermal breakage, as they are not exposed to the sun.

Characteristics of the IG unit : The higher the energy absorption factor of the glass, the higher the IG unit heats up under the effect of sunlight. Absorbing glass, Low-E glass or glass on which a reflective film is affixed absorb more heat than clear glass and are therefore more susceptible to thermal breakage.

Thermal inertia of the frame : The higher the thermal inertia of the frame, the longer it takes the temperature of the frame to adapt to external conditions. The difference in temperature between the visible area of the IG unit and the area in contact with the frame (and therefore the risk of thermal breakage) will be greater. The frame color can also have some effect on the phenomenon.

External environment : The external environment (nearby buildings, shadows from trees, etc.) or the building itself (overhanging terrace, canopy, window coverings, IG unit set back the facade) may submit the IG unit to partial and extended shade.

Indoor environment : The indoor environment can significantly increase the difference in temperature between the hot and cold areas of the unit due, for example, to the presence of blinds or drapes, dark objects such as a cabinet behind the unit, stickers or posters affixed to the glass, a ceiling in front of the IG or other indoor shading devices, but also proximity to a heat source (radiator, convector) or a forced air heating or cooling system.

How do you prevent thermal breakage?

Glass normally stands up to these stresses, but may break for specific reasons. In these cases, the quality of the insulating glass unit should not be called into question. When the difference in temperature within an IG unit can reach values higher than 30°C, tempered glass, which stands up to differences in temperature of 100 to 200°C, is used. Using this type of glass may however, generally be avoided by taking into consideration.


What is ultraviolet light (UV)?

In the spectrum, there are three types of radiation: ultraviolet, visible light and infrared. On the ground, we receive from the sun 5% of UV, 39% of visible light and 56% of infrared. Ultraviolet radiation is an electromagnetic radiation of a wavelength shorter than that of visible light (100 to 400 nanometers).

What is the potential reduction in transmission of ultraviolet (UV) energy with Low-E glass?

The reduction in transmission of UV rays depends on the Low-E coating used and the construction of the IG glass (thickness of the glass, type of glass, etc.). Contact us so we can send you detailed information.

Interference fringes (Brewster fringes)

What causes the interference fringes?

A double insulating glass (IG) unit always has four glass-air interfaces. If these surfaces are of very good quality (very flat and of uniform thickness), the different components of the reflected white light (colored according to the wavelength) can overlap (interfere) and reveal, under natural light, a set of colorful fringes that we can observe both by transparency and reflection.

This optical phenomenon appears only under certain conditions of lighting, temperature and pressure when the thicknesses of the glasses meet extremely low tolerances and when these are almost parallel.

As a result of air pressure variations inside the double IG unit, the glasses can take a convex or concave shape which generates an imbalance of the parallelism variable in time. By soliciting one of the glasses by a slight pressure, the one on which is exerted the stress will deform more than the other and the interference fringes will move.

For double IG unit, the appearance of the interference fringes can be limited by the use of glasses of different nominal thicknesses.

The phenomenon of interference is due only to the very high quality of the glasses and the slight variations of parallelism depending on the climatic conditions. It cannot be considered as a defect.

Acoustic performance of glass

What is the difference between the Sound Transmission Class and the Outdoor-Indoor Transmission Class?

Glass has to meet high performance standards and an important part of these performance relates to acoustics.

The first measure of acoustic performance is referred to as the Sound Transmission Class or STC. This metric measures the sound levels for interior building partitions where the main sounds are people talking or office equipment.

The STC rating is a single number value quantifying the ability of a material to resist the transmission of sound. It uses decibel (db) levels measured between frequencies of 125 Hz and 4000 Hz. The higher the STC rating, the better resistance to sound transmission.

The other measure is known as the Outdoor-Indoor Transmission Class or OITC. This metric measures the sound levels for exterior walls (including doors and windows) where the sound sources come from the outside, such as cars. This rating is especially important to architects since it can have the largest impact on building performance.

The OITC rating is used to measure the sound transfer between outdoor and indoor spaces. It uses decibel (db) levels measured between frequencies of 80 Hz and 4000 Hz, making it a better measure for low sound frequencies such as road noise. As the OITC value increases, the better sound resistant the product is.


What causes haze on Low-E pyrolitic coating?

Some haze, i.e., light milky effect can appear on Low-E pyrolitic coating. This phenomenon occurs when specific lighting conditions, especially when a bright sunlight shines directly or partly on the coated glass and when looking through this glass towards a dark background.

This effect is inherent to the crystalline structure of the coating.

This phenomenon is related to Low-E pyrolitic coatings and cannot be avoid.