Velux is the world’s skylight leader with more than 70% of the global market (glass skylights). Hence the advantage of analyzing and comparing its glazing options.
Skylight glazing is - we should not forget - the single most important element to minimize heat loss or unwanted solar heat gains, or to control sunlight and reduce UV radiation.
Tempered vs laminated glass skylights
Velux offers both tempered and laminated glass skylights. More accurately, it offers 6 types of glazing options, of which 5 are of laminated type.
Tempered and laminated glass skylights belong to the «safety skylights» category. Tempered glass has an additional degree of hardness and shatters into small pebbles (not in large shards).
Laminated glass is made of bonded layers of heat strengthened glass. Velux laminated glass is made of two panes of glass bonded together around a vinyl inner layer; this plastic interlayer is designed to hold the glass together if it gets broken (for safety purposes).
Impact Glass options for hurricane prone areas
Though tempered glass is often depicted as the most impact resistant type of glazing for skylights, it can be overcome by manufacturing details. Velux skylights for hurricane prone areas – «Impact glass» and «Miami-dade glass» - use laminated glass, not tempered glass, which says a lot.
More important than the tempered vs. laminated option is the overall skylight U-value (thermal resistance, or insulation value) and its SHGC (solar heat gains) coefficient.
The most energy efficient skylight options
The U-value and the SHGC specifications are the best way of comparing Velux glazing options or of comparing them with the units offered by other manufacturers.
See whether the skylight complies with the “0.30-0.30” standards, that is, a maximum Solar Heat Gains Coefficient (SHGC) of 0.30 and a maximum Thermal Resistance (U-factor) coefficient of 0.30. Only top skylights (including the plastic aerogel skylights) comply with them.
A very low SHGC coefficient (as close to 0.2 as possible) will reduce unwanted solar heat gains to lower levels; and a low U-factor (also as close as possible to 0.2) will reduce heat loss, which is critical in cold climates.
A high ultraviolet UV-blockage coefficient is also advantageous to prevent fading of interior furnishings and floors; this coefficient can now be as high as 95%-99%.
And you may also consider the VT (Visual Transmittance) coefficient. A high Visual Transmittance allows more daylight to enter your building, while a low Visual Transmittance coefficient (say below 60%) will reduce it. You must choose according to the position of the skylight on the roof, and your daylighting needs.
Energy-efficient skylights are more expensive, but they worth their price. Do not undervalue the enormous importance of skylights on your home’s comfort, and on your heating and cooling bills. Do not be fooled by dreams of beautiful views and plenty of daylighting. Skylights can be a source of problems. If you do need a skylight, consider carefully its energy specifications, and take into consideration your climate (by choosing the best suited glazing).
Velux Low-e glass
All Velux glazing options are low-e (what Velux calls LoE3). Low-e glass comprises a metallic coating (bonded to the glass), intended to control solar heat gain and to protect rooms from fading rays.
Low-e glass is critical in all climates, and should follow the rules mentioned above.
skylight Gkass thickness
Single glass skylights are a thing of the past – even if the thickness of the glass pane is considerable. Velux (or Fakro) skylights are two or triple glazing with argon gas fill; the thickness of each pane is part of a larger set of elements, involving technical and design details.
The really important are features as low-e coatings, gas-fill and framing details.
White laminated Skylight glass
Velux “white laminated glass” provide diffused daylighting. According to Velux this type of glazing makes skylights ideal for offices, schools or warehouse applications by providing energy savings and comfort. According to Velux these skylights provide 3 times more protection against solar heat gain, and protection from UV rays.
Be aware anyway. Though it may be advantageous to have a more diffused daylighting, the really important – from an energy standpoint – is the energy-efficient coefficients of the skylight (including a high UV-blockage coefficient). And you should never forget that skylights, whatever their energy-efficiency, will always be a potential source of thermal disruption and problems.
Snow load skylight Glass
Velux has a specific type of glazing for heavy snow areas: the Snowload glass, available in selected sizes for some deck mounted skylights.
You should prefer this type of skylights in cold climates, but do not expect an outstanding performance; this type of glazing is intended to minimize heat loss and to prevent ice dams… but we should not forget that skylights are responsible for some of the worst ice dams. Heat loss through the skylight to the roofing, and the consequent warming of the roofing materials and snow melting, is a powerful formula for ice dams
Velux laminated and tempered Glass for hot climates
Velux doesn’t offer a specific type of glazing for hot climates, though the company has 3 options to respond to moderate and hot climate needs: the previously mentioned white laminated glass, and what the company simply calls the “tempered” and the “laminated” glass options.
Once more do not overestimate the ability of these types of glass to prevent overheating. Even the best skylights are a common source of excess lighting and overheating. So, pay close attention to the glazing energy efficiency specifications. Look for skylights with a low SHGC (solar heat gains coefficient): lower than 0,3 and as close as 0,2 as possible.
Problems with skylights
Deck vs. Curb-Mounted skylights
Indoor and outdoor skylight covers
Leading skylight manufacturers and brands
Plastic aerogel acrylic skylights
Solar tubes vs. glass skylights
Skylights for cold and hot climates
House-Energy.com Video on Glass Skylights: