General

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

D2000 Sealant = .00045

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 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 an 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 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.

Some units are manufactured with what is called a dual system. This is constructed with a vapour barrier on each side of the spacer to adhere to the glass faces, and the perimeter cavity filled with sealant which normally allows more moisture transmission than the vapour barrier. The vapour barrier used in standard units is a product called polyisobutylene with a moisture vapour transmission of 0.015gm/100 in 2/24 hr, which is extremely low.

However Slimlite Double Glazing Units are constructed with a warm edge single sealant D2000 which is the best Reactive Butyl Hot Melt on the market today. This American product has the lowest vapour transmission (MVTR) in the industry today at 0.13 which is a lower figure than polyisobutylene at 0.15. Polyisobutylene lacks structural strength and is therefore unsuitable as unit sealant.

Gas Transmission

Permeance relates to the amount of the inert gas which escapes over a period of years through the perimeter sealant. Current expectations are that the loss will be around 1% or less per year, depending on the gas permeance of the sealant. However again Slimlite Double Glazed Units are sealed with D2000 which has the lowest gas permeance of any hot melt sealant in the market GPR 0.0000574gm. AR/M2/24 hr/mmHg (Argon).

Glass Roofs, Sealants, Heat Absorbing Glasses

Strengths and adhesion is important with hot melt sealants to prevents any slippage which is when one pane slips downwards out of the direct opposition of the other pane, which can cause breakdown. D2000 is a true hot melt Butyl, double glazing sealant and therefore provides outstanding adhesive and structural strengths. It is the only unique reactive butyl sealant on the market with an atmospheric cure with Shore "A" Hardness 45, and unaffected by any in situ heat from heat absorbing glasses. Standard regular hot melt is thermo plastic which never fully cures and can be affected by heat and therefore no consistent shore hardness which can lead to what is termed slippage in certain circumstances. It is known in the trade that there are problems with some hot melt sealants with some coated glasses in conservatory  roofs, where the glass absorbing heat transmits this to the hot melt sealant, changing its properties which can lead to breakdown. D2000 because of its particular cross linking and mechanical bonds can be recommended for the demanding conservatory roofs and is unaffected by heat build up.

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, similarly with air which is slightly lighter than argon. Generally the heavier the gas the better the insulation, but only in smaller cavities. Krypton and Xenon are much heavier gases and therefore provide the optimum insulation in the small cavities of Slimlite.

However both are very expensive gases, but because of the very small cavities of Slimlite 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. Slimlite will be investigating the sound reduction of Slimlite Double Glazed Units for future reference, but expect the sound reduction of Slimlite to be an improvement on standard double glazing. The width of cavity or overall thickness has little or no effect on sound insulation.

Advantages of Slimlite

1. 5mm perimeter deep seal - for single glazing rebates.

2. 11mm, 12mm and 14mm thickness - for single glazing rebates.

3. Super Spacer - Warm Edge Spacer.

4. Lowest vapour transmission sealant (MVTR) on the market.

5. Krypton and Xenon. Best insulating gas available.

6. Low emissivity glass Low E Pilkington Hard Coat.

Light transmission 75%. Clear glass 81%

7. Units edge protected with waterproof tape.

Slimlite is constructed with the best insulating glass materials currently available in the market today.