New Document L of Building Regulations - effective 1st April 2002

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Condensation on external glass surfaces

External condensation (dew) can occasionally occur on highly insulating glass units in temperate climates. Such occurrences will only happen on cloud-free nights when there is little or no wind and usually when a warm front follows a dry spell.

Attention residents of England & Wales

New Document L of Building Regulations - effective 1st April 2002

NB - If you live in Scotland, Northern Ireland & the Republic of Ireland - CLICK HERE for details about your region.

Effective 1st April 2002 - all replacement window installations in England & Wales will be subject to BUILDING REGULATIONS.

This new regulation in particular affects the minimum levels of insulation that replacement windows must have when fitted in your home. Levels of insulation are measured as U values. The lower the U value, the better the insulation level. In future what we may have in the past have referred to as "normal" double-glazing - i.e. two pieces of glass separated by a spacer bar is very unlikely to conform to building regulations. To get the required level of insulation it's almost certain some sort of LOW E glass (typically Pilkington K in the UK - although there are other brands) will have to be used. It may also be necessary for the sealed double glazed units to be Gas Filled (probably Argon).

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The minimum U values

PVCu or timber replacement windows should not have a U value higher than 2.0 W/m 2K
Metal windows (Aluminium) replacement windows should not have a U value higher than 2.2 W/m 2K
All orders placed after 1st April 2002 needs to comply with the new regulations.
Orders signed before 1st April 2002 will not fall under the regulations provided that the installation is carried out before 1st July 2002.

Exceptions to new Doc L

Conservatories will not be included when the standard commences provided they are separated from the rest of the building (for example by doors) or they are unheated.
Historic buildings are expected to "achieve the best they can".
Also when replacing a broken sealed unit, it can be replaced "like for like". The regulations apply to the entire window replacement.

Condensation ExplainedWith so many replacement windows being installed its been agreed that the industry could adopt a "self assessment" method for administering the many thousands of window installations occurring weekly that will now be subject to building regulations. Basically this means that it will not always be necessary for a building control officer to inspect each installation or for companies to make separate Building Regulations applications.

The Self-Assessment Scheme is referred to as F.E.N.S.A. - Fenestration Self Assessment Scheme. If your contractor is registered with the FENSA self-certification scheme, that contractor may certify that the work complies with the relevant regulations and you will not need to notify the council.

If the retailer is not a member of a Self-Assessment Scheme or the householder is carrying out the work (DIY?) then they will be required to pay for the building regulations application - check with your local council for costs. The time taken to obtain approval will depend on the local authority concerned.

Its very important that all householders recognise the importance of conforming with these new regulations - its very likely that on any future sale of your property you will need to provide proof that you conformed with Doc L.

What about Scotland, Northern Ireland & the Republic of Ireland?

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Scotland has its own Building Regulations. As far as conservation and fuel & power is concerned, the Scottish equivalent to Part L is Part J. New Part J regulations came into force in Scotland on March 4th 2002. You should take advice locally as the application of these new regulations is different to England & Wales - placing more responsibility on the building owner. For more information on the Building Standards for Scotland: Part J visit:

Northern Ireland

Northern Ireland has its own Building Regulations. Although broadly similar, they do differ in some important ways. In so far as Conservation of Fuel & Power is concerned, the Northern Ireland equivalent to Part L is Part F. For more information click here.

The Republic of Ireland

The Irish Republic's equivalent to our Part L is also called Part L.

Recently the Minister for the Environment, Heritage and Local Government, Mr. Martin Cullen T.D., has announced the launch of a public consultation process concerning his proposals to amend Part L (Conservation of Fuel and Energy) of the Building Regulations.

This amendment proposes to amend Part L2 of the national Building Regulations relating to buildings (other than dwellings). This follows on the introduction of improved thermal performance and insulation standards for new dwellings introduced by the Minister on 1 January 2003, and for replacement external doors, windows and roof lights in existing dwellings from 1 July 2003.
For more information visit:$FILE/Part%20L.pdf


The short answer - is as a result of the Kyoto Protocol.

The Kyoto protocol was signed at the earth summit in Kyoto, which is in Japan. The British government and many other governments signed up to a reduction in carbon dioxide emissions to the pre 1990 level. The British government is committed to reduce carbon dioxide to pre 1990 levels by the year 2010 and to continue to reduce emissions, which cause global warming.

click here for a free brochure Carbon dioxide is caused by the burning of fossil fuels, that's coal, gas, oil or similar to make electricity for use by householders or businesses. Motor cars also burn fossil fuels in the form of petroleum, which produces carbon dioxide. The government can achieve its targets by a variety of measures, one is to insulate homes so that the energy required by a home is much reduced, the other is to tighten up on emission controls from motor cars, hence the recent tax changes to company cars and similar. There are a whole range of other efforts to reduce carbon dioxide emissions including wind power, solar power and a revisiting of nuclear power. The objective is to reduce the amount of carbon based products that are actually burned letting carbon dioxide into the atmosphere and to reduce global warming.

Domestic dwellings are said to use about 25% of the energy consumed in the United Kingdom. Therefore over the last few years the building regulations have had a new section called Section L or Document L and this is titled conservation fuel and power. Every few years Document L is reviewed and the requirements for conservation of fuel and power are increased. Some years ago, perhaps four or five years ago, the building regulations required all houses to be built with double glazing and limited the window areas in houses. If you wanted to have large windows you had to do things like introduce Pilkington K into them. What's happened recently is that Document L has been tightened again for buildings and a whole series of changes have been introduced, including cavity wall insulation, loft space insulation, floor insulation etc. Building details generally have changed with the objective of cutting down the energy requirement.

For more information on U Values please see

For more information on Pilkington K Glass see

>>>> Possible Future Performance Standards for Part L: October 2003 <<<<

The Building (Amendment) Regulations, SI 2001/3335 and the publication of the 2002 editions of Approved Documents L1 and L2 convey major improvements in energy performance standards in the Building Regulations. However, as described in the June 2000 consultation paper, these changes were only the first of four stages of proposed improvements in the requirements and associated approved guidance that were expected to be introduced in the period up to around 2008.

However it now appears that The Office of the Deputy Prime Minister (ODPM) (The Goverment office responsible for Building Regulations) wishes to "speed up" the process of these proposed improvements and it has produced a 25 page document which appears to indicate that the Goverment wishes to bring England in line with Scotland at a U value of 1.8 - by 2005. Follow the links below for fuller details.

Two Versions of this document are available - either in a PDF format - or a Word Doc - chose a link below:

The PDF download needs to be viewed using Adobe's FREE Acrobat Reader - available at


Our grateful thanks to Zenith Windows for their help in putting this section on Document L together. Click on the banner below to visit the Zenith Windows web site.

Zenith Windows

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