It is anticipated that the improved energy efficiency measures will save one million tonnes of carbon per year by 2010 (equivalent to emissions from more than one million semi-detached homes). Sections of the regulations will be updated incrementally. The first changes, to Parts F (ventilation) and L (fuel and energy conservation), came into effect on 6th April 2006.

The revisions to Part L set maximum carbon dioxide emissions for whole buildings. The regulations will apply both to the construction of new buildings and renovation of existing buildings (with a total surface area over 1,000m²). For new buildings, it is anticipated that Part L will reduce carbon emissions by 25% from 2002 standards which already reduced emissions by 15%. The net reduction of 40% from pre-2002 is often used as an indicator of improvement.

• Higher quality of construction through the development of robust standard details
• Improved skills in the construction workforce
• Innovation in construction materials, components and building design innovation
• Culture of continual improvement.

Summary

In theory, one of the great distinguishing factors of this Part L from previous Parts is that it tries not to be prescriptive. Targets are set, but the building designers have an element of flexibility in how they achieve the target emissions rate, by the use of more thermally efficient fabric, efficient plant and even renewable micro-generation.

• Section 1: Capping the carbon emissions allowed to be designed into the building
• Section 2: Imposing minimum construction quality criteria.

• Section 1: The type of work to a building when a ‘consequential improvement’ (energy efficiency improvement) to the rest of the building is triggered and the criteria for how feasible the consequential improvement has to be
• Section 2: Guidance on the efficiency measures that should be brought to bear when large extensions, small extensions, conservatories are added, when there is a material change of use or alteration or when controlled or fixed services (lighting, heating, cooling and ventilation) are upgraded or expanded.
• Section 3: Guidance on dealing with ‘thermal elements’ (walls, roofs and floors) and taking reasonable steps to limit heat gains and losses.

Areas of focus

New Build

L2A Section1: Design standards

Carbon emissions are capped by creating a target emission rate (TER), measured in kgCO2/m2/year. The predicted emissions from the actual building design are known as the building emission rate (BER) and may not exceed the TER.

The TER is calculated by:

1. Modelling a notional building of the same size, shape and use as the proposed building, but with 2002 Building Regulation energy performance values.
2. Energy efficiency improvement and low and zero carbon (LZC) energy source factors (laid out in Section 1 of L2A) are then applied to the ‘notional building’ to calculate the emissions reduction required from the notional building. Typically this would be 25% better than 2002 Regulations. The factors differ according to whether the building is to be heated and naturally ventilated, heated and mechanically ventilated or air-conditioned.

Criterion 1 – Achieving an acceptable building CO2 emission rate: The BER is calculated by using the same calculation tool as used for establishing the TER. Normally this is the Simplified Building Energy Model (SBEM). The final calculation takes into account any changes to specification made during construction and the measured air tightness on commissioning (see Section 2 of L2A). Adjustments are made for fuel types and for enhanced management controls as per Tables 2 and 3 of Section 1.

Criterion 2 - Limits on Design Flexibility: Elements of a building (walls, floor, roof, windows, pedestrian and vehicle access doors) are given an area-weighted average minimum thermal conductivity efficiency value (known as the U-value). However, individual parts of the element have less stringent values. For example a window will have an area-weighted average U-value of 2.2. However, individual parts (such as the frame) may have a U-value of up to 3.3, so long as the overall average including the glazing is 2.2. This gives marginal flexibility in how the overall U-values are reached. [Lower U-values indicate a better insulating material.]

• Controls for heating, ventilation, air conditioning subdivided into building ‘zones’ with default setting as ‘off’.
• Energy meters to enable at least 90% of energy consumption for each fuel to be assigned to its end use category. For buildings over 1000m2, automatic meter reading and data collection facilities are required.
• There are additional requirements for the ‘reasonable provision for the performance’ of ‘suitably efficient’ heating and hot water, cooling, air handling plant and pipe and duct insulation. Lighting standards and controls are also identified.

Criterion 3 - Limiting the effects of solar gains in summer: ‘Provision should be made to limit solar gains so as to reduce internal temperature rise in summer… designers …may wish to go beyond the requirements of Building Regulations to take more account of future global warming…’ Reasonable provision seems to involve following the guidance of the CIBSE design guide A.

L2A Section 2: Quality of construction and commissioning

1. Air permeability and pressure testing (10m3/hour/m2 at 50 Pa), except very large and complex buildings. Buildings of less than 500m2 do not have to be tested, but their BER design must have used a permeability of 15m3/hour/m2 at 50 Pa. If the building fails this test, remedial action will be taken until it can pass. There is a grace period until 31 Oct 2007, in which remedial action will only need to improve 75% of the difference between the initial and desired results.
2. Commissioning of the building services systems: the systems and their controls will be tested to show that they are in working order for the purposes of energy efficiency.

Refurbishment

Refurbishment or ‘other building work’ is split between smaller changes to the building, which require the building work to meet specifications in Section 2 and major refurbishment which triggers a ‘consequential improvement’ for the whole building, covered by Section 1 and the beginning of Section 2.

L2B Section 1: Consequential Improvement

• an extension
• the initial provision of any fixed building services such as heating, ventilation or air handling
• an increase to the installed capacity of any fixed building service

the whole building will be required to comply with Part L if this consequential improvement is technically, functionally and economically feasible.

Economic feasibility requires a simple payback not exceeding 15 years. In the case of extensions, the consequential improvements must cost not less than 10% of the principal works. Cost effective examples are given including upgrading most heating, cooling and air-handling systems which are over 15 years old. Introduction or increases to micro-generation systems (low and zero carbon technologies or LZC) are considered economically feasible if they have a pay back period of 7 years or less.

Where building services are being installed or upgraded, two sets of improvements are required.

1. Firstly improve those parts of the building served by the services
2. then, make improvements to the rest of the building fabric. Costs incurred in (1), do not count towards the overall ‘economically feasible improvements’ of (2).

L2B Section 2: Guidance relating to building work

For smaller extensions, the fitted services should meet standards listed later and fabric should meet the standards suggested in Section 3. The surface area covered by windows and roof lights in the new extension is limited.

Conservatories over 30m2 must be thermally separated from the building, in so far as the separating walls and doors meet the criteria in Section 3. If not thermally separated, it counts as an extension. Smaller conservatories are exempt.

Where there is a material change of use (such as conversion to residential) or a material alteration (where a change causes an element to no longer comply with Building Regulations), the same general rules apply as for extensions.

Work on controlled services and fittings: heating, hot water, lighting and cooling and air handling plants must meet minimum efficiency criteria and be correctly commissioned. The minimum efficiency may not be less than that of the system being replaced. Where a new fuel type is being used the efficiency should be adjusted by the relevant CO2 emission factor.

The new systems must have separate controls for each ‘zone’ corresponding to solar exposure, occupancy period or type of use. Central plant serving the zone-based systems should have a default setting of ‘off’. Heating and cooling may not be permitted to operate simultaneously. Energy meters should be installed to assign at least 90% of energy consumption to its end use category.

Fittings, including windows, roof lights, doors and vents must be draught proofed to specified standards.

L2B Section 3: Guidance on thermal elements

Provision is new or replacement elements. Renovation: if more than 25% of the element is being renovated, the whole must meet the specified U-value. For less than 25%, no upgrade is needed. If an element is retained as part of a material change of use or becomes part of the ‘thermal envelope’ (e.g. an internal wall becomes an external wall) the whole must be upgraded if it can be done within a 15 year simple payback.