Building Regs Part L

by Steve on November 1, 2009

Building Regs  Part L         

Conservation of Fuel & Power

This section covers energy efficiency with regard to lighting and heating.

The regulations are likely to change frequently as the EU Directives strive to reduce carbon emissions and more energy efficient products become available.


Fixed internal lighting

Relevant to new buildings, extensions and rewires.


-1 x energy efficient light fitting per 25 sq mtrs  or

-1 x energy efficient light fitting per four fixed light fittings (25%)

whichever is greater.



Fixed external lighting

-External lighting must be automatically controlled to switch off in daylight and when not required and have a maximum lamp capacity of 150 watts   or

-be an energy efficient light fitting.



Electric Boilers serving wet central heating systems

and  Electric Heating (other than Boilers)


-Electric Warm Air Heating

-Electric Panel Heaters

-Electric Storage Heaters


The main requirements for these systems relate to Energy Efficiency and Controls.

Electricians should be aware that:

-Dwellings with a floor area below 150 sq mtrs should be divided into at least 2 zones with independent temperature control, one of which should be assigned to the living area   and

-Dwellings with a floor area above 150 sq mtrs should be as above but with separate timing and temperature controls.


Boiler Replacements:

-Gravity systems should be converted to fully pumped

-New controls should be installed unless they are already installed and operational.


The Domestic Heating Compliance Guide- Compliance with Approved Documents L1A (New Dwellings) and L1B (Existing Dwellibngs) can be downloaded from:


Thermal Insulation

Today’s more energy efficient buildings methods require high levels of thermal insulation.

Electricians must be aware that circuits designed to use cable installation methods  (for flat twin & earth) 100, 101 and 102 must not be totally enclosed in thermal insulation. 

One side of the cable must be in contact with a thermally conductive surface.


Installation methods 103 relates to cables which are not in contact with such a surface and are subject to a de-rating factor of 0.5.


It would be advisable to make the builders and other trades aware of these thermal design limitations and also that luminaries must not be covered unless suitable.

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