Gaseous glazing

The UK government has introduced legislation that will help to reduce environmental pollution and conserve irreplaceable natural fuels. One of the main areas of the legislation deals with energy-efficient buildings.

Global warming is arguably the greatest single environmental threat facing humanity. All records for average global temperatures which have been maintained since the mid-nineteenth century have been broken in the last 20 years.

It’s something that many national governments are taking seriously, too. At the 1997 Kyoto world climate summit agreement, each of the 38 participating countries agreed to reduce their greenhouse gas emissions by 5% from 1990 levels by 2010.

As a result, the UK government has introduced legislation that will help to reduce environmental pollution and conserve irreplaceable natural fuels. The penalties for companies not following these regulations are steep – fines of up to £5,000 are being issued to companies for non-compliance.

One of the main areas the legislation deals with is energy-efficient building. The reason this matters is because the energy we use to heat, light and cool our buildings accounts for almost half of all the UK’s carbon dioxide emissions – one of the ‘man-made’ gases responsible for contributing to the greenhouse effect.

New building regulations state that relevant businesses (for instance, double-glazing manufacturers and installers, or construction companies working on new buildings or making changes to existing ones) must now follow revised standards of thermal insulation and energy efficiency.

These changes concern the construction of energy efficient building elements (such as walls, windows, floors and roofs) and building services (such as lighting, heating and ventilation).

Replacement glazing also now comes within the scope of the regulations, so anyone who installs new replacement windows or doors will now also have to comply with strict, mandatory thermal performance standards.

In England and Wales, the relevant regulations are the Building Regulations 2000 as amended by the Building (Amendment) Regulations October 2001, Part L Conservation of Fuel and Power. The changes were extended in April 2002 to cover replacement window and door installations. The 2001 editions of Approved Documents L1 and L2 give help in interpreting the regulations.

Newly installed windows (glass plus frame), and any replacement door which is more than 50% glazed, must now meet a required ‘U value’ (a measure of the energy efficiency of the glass and frame) of 2.0 W/m2K (watts per metre squared, kelvin). The value for U-PVC and wood framed windows is also 2.0 W/m2K and for aluminium or steel framed windows it’s 2.2 W/m2K.

Scotland has its own Building Regulations. The Scottish equivalent to Part L is Part J, and new Part J regulations came into force in Scotland on March 4th 2002. The 2001 ‘Technical Standards’ document gives guidance on meeting the requirements.

In Scotland, the maximum permitted U value for windows, doors and roof-lights in non-domestic dwellings is dependent on the heating system’s fuel and boiler efficiency. With boilers that do not meet the performance figures set, or for any electric or solid fuel system, the maximum U values are tightened to 1.8W/m2K for U-PVC and timber windows, and 2.0W/m2K for aluminium and steel. If the boilers meet the figures, the U values are as for England and Wales.

Northern Ireland has its own Building Regulations, the Building Standards Amendment (Northern Ireland) Regulations 1994. Although broadly similar, they do differ in some important ways. The Northern Ireland equivalent to the England and Wales Part L is Part F. Technical Booklet F, Conservation of Fuel and Power, December 1998 provides guidance on the interpretation of the Regulation requirements.

There are five key factors involved in making energy efficient windows: glass type, cavity size, frame design and material, triple gazing (rather than double glazing) and cavity filling gas.

In more detail, these options are:

<UL><LI>Using low ‘E’ (emissivity) glass. ‘E’ glass is coated in a reflective surface that reflects heat back into a building. The lower the ‘E’ rating, the more heat it will reflect back.<LI>Increasing the cavity size.<LI>Using wood or U-PVC frames, which have better insulation properties than metal frames.<LI>Using triple glazing rather than double glazing.<LI>Filling the cavity with argon gas or an argon/krypton mix, both of which have better insulation properties than air.</UL>

Coating glass surfaces also reduces visibility through the window, and increasing cavity sizes and triple glazing add to the weight and cost of manufacturing of the window.

It seems that the most energy efficient solution is a combination of several or all factors – for example, low rated ‘E’ glass with a cavity of 16mm filled with argon in a U-PVC frame.

Because argon’s and krypton’s thermal conductivity is much lower than air, they are both ideal for keeping U values low in sealed double-glazing units, either combined with each other or each with air.

A mixture of argon and krypton has better insulating qualities than argon alone and allows manufacturers to achieve even lower U values when necessary and to produce Building Regulations compliant windows with cavity sizes smaller than 16mm. This naturally has implications for weight and cost. An argon and krypton mixture is used extensively in double glazing in North America (principally Canada and California), Scandinavia and Germany.

The preferred methods of demonstrating a window’s compliance with the new Part L regulations are ‘hot box’ testing or the CoG (Centre of Glass) calculation both of which are to the established European standard.

If neither of these can be performed, the government has calculated minimum (default) values which may be used.

If you would like to find out more, visit:<a href=’′></a>.

Alternatively, for more detailed information on the regulations visit the DTLR / Building Regulations website <a href=’’>here</a>.

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