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The benefits of specifying fixed flat skylights are clear: they provide high levels of natural daylight, and they contribute to the thermal comfort of a building. Skylights also provide an aesthetically pleasing addition to the external appearance of a property.

Most modern skylights are designed using lightweight aluminium or steel frames for several good reasons: providing great weight saving and strength, and also require little maintenance, compared to wooden frames.

However, these types of material are extremely efficient conductors of heat, which means that during winter you can lose heat from inside your building via direct transfer through the skylight frame. Conversely, if you have warm, humid air inside the building making contact with the cold frame surface, condensation is likely to form where ‘cold bridging’ occurs, if no thermal break is present or the thermal break is poor.


The Glazing Vision fixed Flushglaze skylight has a silicone sealed finish both of the skylight to the aluminum and the insulated glazed unit.  A low modulus silicone is used as this performs better to UV, the low modulus factor means the skylight can accommodate thermal movement better.

Different to other skylight products on the market, such as the skylight shown here – where the aluminum is very thin and also extends up and over the glass.  This creates a possible dirt trap and danger of water ingress into the building and indeed that is why this skylight has a condensation channel.

No condensation channel is required on the fixed Flushglaze range, or indeed any of the Glazing Vision range due to the flush frame finish.  Any water will simply run off the side of the skylight.

The fixed Flushglaze skylight gives an excellent performance when installed correctly.  Everything on the Flushglaze is sealed, using foam backing rod, silicone and structural adhesives.  There is no way for air or water to penetrate into the building.


The main contributory factors of condensation on skylights are:

1. Cold bridging – where you have warm air meeting cold air, all Glazing Vision products contain a thermal break, on the Fixed Flushglaze this is created by a bubble seal as can be seen in the image. This prevents the framework coming into contact with the inside of the building.

2. Insulated glass unit performance – all Glazing Vision skylights come with a warm edge spacer bar which helps prevent cold bridging around the edge of the IGU.

3. Fixing to the curb, this is a big factor in skylights that we are requested to inspect due to condensation. Getting a good seal all around the skylight to the curb is essential.  Any air getting into the building can meet the air of differing temperature on the inside of the building and this causes it to change the temperatures close to the glass and form condensation on the glass.  You can test the seal of the skylight yourself by holding a candle close to where the skylight sits on the curb on the inside (on a windy day).  The candle will flicker due to the air leakage.

4. Pockets for trapped air, you need to consider if there are areas where air will be prevented from circulating and become trapped. Over time that air will become stale and this can lead to a temperature difference and cause condensation.


The cavity between the panes of glass is also filled with argon gas as opposed to air in all Glazing Vision skylights, argon has a slower conductor factor than air meaning that it will take longer to be affected by inside/outside temperatures than air.

Consideration should also be given to the glass specification chosen.  Most IGU’s now come with Low E as standard to offer some improved thermal performance.  Note that the glass used in the right-hand image is very thin.  It is also tempered/tempered glass, this is classed as a fragile glass, as if it were to shatter then someone could potentially fall into the building.

Most Glazing Vision skylights come with a laminated glass, these are considered to be non-fragile as if they ‘crack’ they are held together by the laminate and therefore offers a reduced risk of someone falling into the building.  When choosing a skylight you must consider potential maintenance loads, wind loads and snow loads for the area of installation.

Glazing Vision offer a no leak guarantee on all our skylights when installed to our recommendations or by an approved Glazing Vision installer and have recently been tested to ASTM standards:

  • ASTM E283 Air permeability.
  • ASTM E331 Water penetration.
  • ASTM E330 Structural performance/wind resistance.

For more information on our flat fixed skylight range, browse our complete range or make an enquiry for further technical advice.

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