Approved Document L2B - Designing Existing Buildings Other Than Dwellings
Approved Document L2B 
provides guidance on complying with the requirements of Regulation L1 dealing with the conservation of fuel and power on existing building. It is one of four Part L Approved Documents.
We will outline the energy performance standards required for existing buildings which are not or do not contain dwellings, but also includes alterations to buildings containing 'rooms for residential purposes' such as nursing homes and student accommodation or the common parts of apartment blocks which are outside the scope of L1A and L2A .
From the 6th April 2006 all newly extended and some altered buildings other than dwellings, will need to comply with the design considerations given in the Approved Document.
Types of work covered
The following types of work come under control from this Approved Document:
- Extensions to buildings other than dwellings (except those greater than both 100m² and 25% of the floor area of the existing building - in which case Approved Document L2A should be used);
- The Material Change of Use of a building, (or part) that will require the renovation and upgrading of existing thermal elements and replacement of windows;
- Material alteration, renovation or extension of thermal elements and controlled services; and
- Consequential improvements to improve the energy efficiency of the whole building required when increasing the stored capacity of heating or cooling plant.
Technical interpretation
We will give guidance on specific aspects of building work. We do not intend to fully demonstrate compliance, but merely be a handy guide for designers.
Renovation of thermal elements (walls, floors, roofs)
Where more than 25% of the surface area of a thermal element is being renovated the whole of the element should be upgraded.
If such an upgrade is not technically or functionally feasible or would not achieve a simple payback of 15 years or less the best achievable standard will be acceptable.
Work on historic buildings
Special considerations apply if the building work is associated with a building of special historic or architectural value. The aim should be to improve energy efficiency where practically possible, provided that the work does not prejudice the character of the host building or increase the risk of long-term deterioration to the building fabric or fittings.
Consequential improvements
Where an existing building with a total useful floor area over 1000m² and where the proposed building work consists of or includes:
- An extension, or
- The initial provision of any fixed building services, or
- An increase in the installed capacity of any fixed building services,
Then additional work, known as 'consequential improvements' need to be carried out, provided that these works are technically, functionally and economically feasible. A minimum achievement of at least 10% of the value of the principal works is the target set. The use of a suitably qualified person such as a chartered quantity surveyor may be able to assist in the financial interpretation of the works.
The type of works which should be considered include:
- Upgrading heating systems with new plant or improved controls,
- Upgrading cooling systems with new plant or improved controls,
- Upgrading air handling systems with new plant or improved controls,
- Upgrading general lighting installations over 100m²,
- Installing energy metering,
- Upgrading thermal elements,
- Replacement of windows, roof lights and doors, and
- Increasing on site LZC energy generating systems.
However, all these issues (above) are subject to constraints in terms of age and economic payback periods, which are factored into the overall assessment.
Issue of completion certificates
We will not generally be able to issue certificates of completion under the Building Regulations until they have received: -
- Details of the U values of elements,
- Any assessment of the consequential improvements necessary, and
- Any relevant certificates for the commissioning of controlled services in the building.
Construction standards and design detailing
Irrespective of the quality of insulating materials used, there is a major potential for heat loss and cold bridging caused by poor standards of construction in terms of air tightness and the continuity of insulation. For this reason it is important for the designer to ensure that the various insulated elements in a building are carefully detailed at junctions. Uncontrolled air leakage can be minimised by specifications calling for appropriate levels of sealing and The Stationery Office Robust Details Guide 'Limiting Thermal Bridging and Air Leakage' suggests suitable details for achieving this with typical methods of construction.
Site supervision
The importance of effective on-site supervision to oversee the quality of workmanship achieves the above standards should not be underestimated. The cost of delays in completion and remedial action could far outweigh the costs incurred in this process.
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