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Document L

Document L came into force in April 2002. Under Document L, all replacement windows have to be double glazed with a Low-E glass, and meet a certain U-value. The term "windows" applies to the frame and double glazed unit combined. If only the double glazed unit is changed, this can be done on a like for like basis.

What is Document L?

Document L is the part of the Building Regulations for England and Wales that sets the standards of energy efficiency in buildings.

Why were the changes introduced?

The UK Government has made commitments to reduce emissions of greenhouse gasses such as carbon dioxide which are harmful to the environment.

Does Document L apply to all buildings?

Document L covers the construction of new dwellings and non domestic buildings such as offices and public buildings. It also now includes replacement windows installed as home improvements.

Do the requirements apply to repair work on existing windows?

Document L only applies when the whole window is to be replaced. Replacement of just the glass or part of a damaged frame is exempt from the regulations and the replacement can be carried out on a like for like basis.

Are there any exceptions?

Listed properties and buildings in conservation areas may be exempt as are display windows and shop entrance doors. Replacement doors that have a glazed area of less than 50% are also exempt. Conservatories are exempt providing they are unheated and separated from the house.

Why do I have to comply with the regulations?

Complying with the Building Regulations is a legal requirement.

What is a U-value?

The U-value measures the rate at which heat is lost through a material. The lower the U-value the lower the amount of heat lost and the lower the amount of energy wasted through the window. U-values are measured in Watts per square metre per degree of temperature difference (W/M2K). Upvc windows should have a U-value of 2.0 W/M2K.

What is Low-E glass

Low-E stands for low-emissivity. The double glazed unit has one of its inside faces lined with a special coating that lets heat and sunlight filter through but reflects any heat trying to escape back into the room.

The benefits of Low-E glazing are: Reduced heat loss, eliminates cold spots and reduced condensation. Low-E glass is available in annealed, toughened and laminated glass.

How is Document L enforced?

New build is monitored through building control approval. Replacement windows can also be monitored in this way but this is very time consuming and expensive. The preferred method is via a self-certification scheme such as Fensa, BM Trada Certass. All these companies do the same job.

The Self Assessment Scheme

Over one million installations of replacement glazing happen every year. it would be impracticable for all these to go through the Building Regulations application process. Various schemes were set up to allow installation companies that meet certain criterion to self-certify that their work complies with the Building Regulations. The scheme I am using is known as BM Trada.

A sample of the work of every installer will be checked by BM Trada appointed inspectors to ensure standards are maintained. BM Trada will also inform local authorities of all completed installations and issue certificates to householders confirming compliance.

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