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Most standard double glazed units are constructed with cavities around 16mm to 20mm and filled with Argon gas. The wide cavities are necessary to achieve the required insulation or U Value. Argon is a light gas and necessary for wider cavities. Argon cannot produce the best insulation in small cavities which require Krypton to provide the best results.

Some standard double glazed units still use an aluminium spacer to provide the required cavity. However this causes a cold bridge around the perimeter evidenced as condensation around the perimeter in cold conditions.

Slimlite Ultra Clear and Slimlite Standard Self Cleaning Units by using a warm edge spacer, which is now becoming popular avoids this problem, as the difference in insulation from center to perimeter is almost nil.

Example: Slimlite Ultra Clear and Slimlite Standard Self Cleaning Units

Constructed: 4mm Low E/4mm Cavity, gas/4mm Clear - U Value 1.9 BSEN673
National Physical Laboratory Report on total overall U Value 1.96 BSEN8990.



Double Glazed Units are basically 2 panels of glass held together around the perimeter with a spacer and sealant to hold them apart. The air or inert gas if used remains still within the cavity and creates a measure of insulation. However there are variable restrictions on cavity widths for air and inert gases, and if these cavity widths  are exceeded, internal convection occurs within the cavity. This movement of air or gas contacts the cold outer pane surface and transfers by movement between panes and thereby reducing the insulation value.

Glass Insulation

To obtain maximum insulation from a double glazed unit it is necessary to use the lowest possible conductive materials. The conductive value of glass is well known, but most double glazed units manufactured today are constructed with an inner pane of low emissivity glass or Low E, which is coated glass, where the coated face, faces into the cavity, which effectively reflects the long wave radiation or heat back into the room maintaining a measure of insulation.

Heat Conductivity of:

Wood = .0003

Warm Edge Technology

The selected spacer and sealant for double glazed units is very important. The spacer used in some units is a rectangular aluminium section a cold metal and therefore has a cooling effect around the perimeter insulation. To overcome this effect Slimlite Ultra Clear Self Cleaning Double Glazing is constructed with a Warm Edge Spacer referred to as Super Spacer, an American product which has the effect of ensuring that temperature or insulation is not significantly different from the centre, to the perimeter ensuring that the condensation sometimes evidenced around the perimeter of some standard units does not occur as super spacer is a structural warm foam spacer which has integral drying agents.

Hot Metal Sealants and Vapour Transmissions

Most sealants used in the perimeter of double glazed units today are regular Hot Melt, which is applied to the perimeter cavity at a hot temperature of approx 190ºC but cool very rapidly to provide the adesive seal. However not all hot melt systems are the same and can react differently in various exposures. They also have varying adhesions, permeance and vapour transmission. The most important factor in double glazing units apart from the insulation is the vapour transmission (MVTR). This occurs through the sealant from external moisture or water but is not visible. If the sealant has a high transmission rate the unit will in a relatively short time break down, which is the visual condensation which can be observed.

This occurs when the spacer holding the glass apart which has a drying agents which is intended to absorb any moisture present in the manufacture of the unit, can no longer absorb the moisture caused by the transmission through the sealant into the cavity, resulting in condensation inside the unit. This occurs when the glazing fails to protect the unit from the ingress of water.

Gas Leakage

slimlite - Gas Content - Gas Leakage Certificate BSI 371/7758378 Krypton inert gas

Double Glazed units have a gas leakage rate and are required to have a gas leakage certificate at a rate less than 1% per annum which is BSEN1279 Part 3. The standard gas fill required is 90%, but Slimlite has an average fill of 96.6% and is certified average leakage loss at 0.77% per annum. Therefore Slimlite has approximately 7% more gas over a period of 10 years at 89.32% and 20 years at 82.67% compared to a standard unit gas 90% fill with resulting loss at 79.33% at 10 years and 74.33% at 20 years. Loss of inert gas will decrease the insulation of a double glazed unit which is important in today's escalating energy costs.

Insulating Gas

Inert insulating gases are used in the cavity of double glazed units to improve the insulating factor, and the best results are obtained with Low E glass and inert gas. There are various inert gases on the market which perform in different width of cavities. The most common and cheapest gas is argon and will perform in cavities up to 20mm.

Cavities over 20mm will decrease their insulation effect as internal cavity convection would occur. Generally the heavier the gas the better the insulation, but only in smaller cavities. Krypton is a much heavier gas and therefore provides the optimum insulation in the small cavities of Slimlite.

However both are very expensive gases, but because of the very small cavities of Slimlite Ultra Clear Self Cleaning Double Glazing the costs are economical for their insulation values. As they are heavy gases with larger molecules they have an added benefit of sound reduction. Generally the heavier the gas the better the sound reduction. The width of cavity or overall thickness has little or no effect on sound insulation.

Slimlite is constructed with the best insulating glass materials currently available in the market today.To ensure that Slimlite Ultra Clear Self Cleaning Double Glazed units are a premier quality product.