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Thermal Requirements

Approved Document L 1995
(Conservation of fuel and power)

Introduction
The amendments to the energy conservation requirements of the Building Regulations Approved Document L came into effect on 1st July 1995. The concept of overall heat loss has been further developed with the introduction of an average U-value approach. In addition, economical design solutions for each part of the building, in conjunction with reduced technical risks, can now be achieved by blancing the heat loss through parts of the structure with the efficiency of the heating system and useful beneficial solar gains.

As an additional requirement to the regulations, all new and converted buildings have to be 'energy rated'. The ratings are based on the Government's Standard Assessment Procedure. SAP ratings range from 1 to 100 (100 being the best). They are derived from an estimate of the annual energy cost for space and water heating per unit floor area of a dwelling in a standard location, assuming a standard occupancy pattern.

The main parameters taken into account:

1. The price of fuels used for space and water heating;

2. Efficiency and control of the heating system;

3. Thermal insulation of the building fabric;

4. Ventilation characteristics of the dwelling;

5. Solar gain characteristics of the dwelling.

Avoidance of Risks
Increasing the air-tightness of buildings and improved energy conservation measures, including fabric insulation, could entail increased risk of condensation and related problems. To minimise this, ventilation requirements Approved Document F have also been revised and teh Building Research Establishment advisory document 'Thermal Insulation: Avoiding Risks' has been updated.

The Regulations
Compliance with the regulations may be shown via three alternative approaches:

Elemental Method
Compliance with the regulations may be shown via three alternative approaches:

The elemental method prescribes maximum U-value for the individual construction elements of the structure, depending on the SAP-rating of the dwelling. The Requirement for insulation of the building fabric will be met where the U-values of the proposed do not exceed those given in Table 1.

Table 1 - Standard U-values (W/m²K) for Dwellings

One way of achieving the U-values in Table 1 is by providing insulation of an appropriate thickness estimated in Table 2.

Table 2 - Insulation Thickness for Suspended Concrete Beam and Block Ground Floors

Note P/A is the ratio of floor perimeter (m) to floor area (m²)

Target U-Value Method
In order to demonstrate appropriate provision for the building fabric, the Target U-value method has been introduced. When demonstrating if a particular building achieves the Target U-value, the designer may take into account the benefits of solar gains through glazing and more efficient heating systems.

The Target U-value for a participating dwelling depends on its SAP rating, the requirement will be met if the calculated average U-Value does not exceed its target.

Energy Rating Method
Any dwelling with a SAP raing of 80-85 (depending on floor area) or more will comply with the requirements of Approved Document L. For dwellings wil SAP ratings of less than 80, compliance will need to be shown by using either of the other two methods.

• Typical Details
• Design Considerations
• Thermal Requirements
• Specifications