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Question submitted on 19th Apr 2002
what is the current requirement in Doc L concerning trickle vents?
David Amos answered on 30th Apr 2002

Document L is an amendment to The Building Regulations 1991 that relates to conservation of fuel and power. The aim of which is to improve the energy performance of all types of buildings when they are newly built and in certain aspects when existing ones are altered or extended.

The amendment has been driven by The Kyoto Protocol and the UK Climate Change Programme. Within Part L of the Building Regulations it states:

  • The Government has agreed to achieve a target under the Kyoto Protocol to reduce emissions of a basket of 6 greenhouse gases. As a result of a subsequent agreement within the European Union, the UK has taken on a legally binding target to reduce its emissions to 12.5% below 1990 levels over the period 2008 to 2012. The Government also has a separate domestic goal of reducing its carbon dioxide emissions to 20% below 1990 levels by 2010.
  • The Government published its climate change programme in November 2000. This document explains why the Government is tackling climate change, outlines the action being taken internationally and in the UK, and describes the proposed strategy to deliver on the Kyoto and national commitments. This strategy includes seeking higher building energy performance standards through this amendment to the Building Regulations.

The aim of Document L is to see a reduction in the energy consumption of buildings via the Building Regulations, whilst maintaining proportionality, design flexibility and avoiding excessive costs and technical risks. Subordinate aims include achieving the following: -

  1. Sufficient flexibility for designers to meet weather and architectural goals that vary throughout the country - in particular to ensure that the character of historic buildings will not be compromised by the new standards for existing buildings;
  2. Avoidance of unacceptable technical risks of for instance rain penetration, condensation and mould growth and avoidance of overheating through excessive solar gain or unsatisfactory ventilation which leads to unhealthy accommodation.

Additionally the amendment has been developed taking into account the need to avoid worsening indoor air quality as a result of: -

  1. Sealing which reduces the ventilation rate. This would increase the risks to safety posed by open-flued combustion appliances and the risks to health posed by reduced dilution of irritants, toxins and other pathogens;
  2. Rain penetration and/or condensation causing damp surfaces on which moulds with pathogenic spores can flourish;
  3. Increased insulation and tighter sealing leading to overheating;
  4. Increasing humidity due to the reduced ventilation; and
  5. More complex ventilation systems that through operational and maintenance failure bring harmful particles into the building.

Again the aim has been to ensure that these risks to health have been kept within acceptable limits. As you can see from the above the aim of Document L is to conserve fuel and power through the improved energy performance of buildings. Whilst ventilation is referred to it is not the objective of Document L. In the context of the Building Regulations a trickle vent would seem to be a form of ventilation.

It is Part F that refers to ventilation and this has also been subject to change. It is important you refer to your copy of the Building Regulations for specific technical details where minimum ventilation requirements are provided for all habitable rooms and bathrooms. The manufacturers of your trickle vent should be able to provide you with the performance levels of their products.

In the form of explanation, The Building Regulations 1991 are a set of minimum requirements to secure the health, safety and welfare in and around buildings and to conserve fuel and energy in England and Wales (Scotland has their own regulations). They are made by the Secretary of State under Powers given by section 1 of The Building Act 1984. Although the Approved Documents (and Document L is one of these) give guidance as to how to meet the requirements of the Regulations, the requirements are set out in a number of Parts. We in the window industry are mainly interested in:

  • Part F - Ventilation and condensation.
  • Part L - Conservation of fuel and power.
  • Part M - Access and facilities for disabled people.
  • Part N - Glazing - Safety in relation to impact, opening and cleaning

Ask David further information >>

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