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Proposed standards for new dwellings

Target emission rate and Standard Assessment Procedure (SAP).

One of the most significant changes is that the proposed new performance standard is based on a target CO₂ emissions rate for heating, hot water and lighting. This would give developers and builders a great deal of flexibility in how they achieve the target. Some might prefer to concentrate on improving the envelope performance by including more insulation in the walls, floor and roof, and specifying better performance windows. Others might wish to concentrate on the systems (more efficient boilers or alternative heating technologies like heat pumps), solar hot water, or mechanical ventilation with heat recovery. The proposed target depends on four factors: the floor area of the dwelling; the ratio of exposed surface area to floor area; the carbon content of the main heating fuel; and a lighting factor.

Renewable energy technologies like solar hot water, and low carbon systems like community chp could have an important role to play in achieving the target performance standard. Although there is no requirement to include any such carbon efficient technologies, the new approach would encourage their adoption especially for those dwellings where gas is unavailable (off the grid) or may be undesirable (eg not wanting pipes distributing gas to each apartment in a block).

The Standard Assessment Procedure (SAP) is the method proposed to assess whether a new dwelling meets the target performance standard. It is already a legal requirement that a SAP rating be produced for each new dwelling, so this approach builds on techniques and expertise already available to builders. SAP is being revised to reflect its use as a means of demonstrating compliance with Part L1. As part of this revision new technical issues have been included, such as the effect of thermal bridges and the impact of lighting specifications on overall energy use and carbon emissions.

Another important issue proposed to be introduced for the first time is a requirement to design the dwelling so as to avoid excessive solar overheating. The intention is to improve summer comfort in new dwellings while minimising the growth in domestic air conditioning. Solar overheating can be reduced by careful selection of size and orientation of windows, the use of shading devices, and the appropriate use of ventilation, often coupled with a high thermal capacity structure. A procedure has been added to SAP to allow designers to assess the likelihood of overheating.

Requirement for pressure testing

Another important new feature of the proposals is the introduction of pressure testing to confirm that the appropriate standard of airtightness has been achieved. Air leakage (or infiltration) is a significant source of energy loss, both through its direct effect of cooling the dwelling, but also because it tends to bypass insulation and reduce its effectiveness. A pressure test is the most effective way to confirm that the quality of design and construction is to a reasonable standard. It is proposed that testing should be on a sample basis, the sampling rate depending on whether or not the builder is using robust details.

The desire to ‘tighten’ buildings to reduce energy wastage has to be coupled with a consideration of ventilation in order to ensure adequate indoor air quality is maintained. Ventilation for health is covered by Part F of the Building Regulations, and so proposed amendments to the guidance in Approved Document F have also been published for consultation and are available from the same ODPM website as the Part L proposals.

Proposals for work in existing dwellings

The main headline from the proposals is that more work in existing dwellings will now be subject to the Building Regulations. The intention is that by capturing this additional work, it becomes possible to incorporate energy efficiency improvements at the most cost-effective point, ie when work is planned. By this approach, there should be a progressive improvement in the energy standards of the existing stock of dwellings. A recently published survey by CABE suggests that 84% of house buyers would consider paying extra for homes with improved energy efficiency and lower running costs. This suggests that these proposals are in tune with consumer demand.

Because the work done in existing dwellings is different in scale and nature from constructing new dwellings, the requirements and the associated guidance covering existing dwellings has been published separately in Approved Document L1B. This Approved Document defines the type of work that is now subject to Building Control, and sets out the standards that are considered reasonable.

Clearly, in some situations in existing dwellings, it is not practical or cost-effective to achieve the standard of energy efficiency that is appropriate for new build. Equally, it is not sensible to discourage people from improving the properties because the cost of achieving the standards is too high for the average homeowner to contemplate. The approach therefore concentrates on achieving worthwhile improvements at reasonable marginal cost.

Improving the whole dwelling

The most important proposal relates to the requirement to improve the whole dwelling once building work of a sufficient scale is scheduled. Previously, only those elements of the building that were being altered or replaced were subject to control. Under the proposals, it will now be necessary to upgrade the whole dwelling, always provided that the marginal costs of doing so are not excessive. For example, if a house was having an extension, as well as the extension itself meeting energy performance standards, the regulations could call for extra loft insulation to be added, cavity walls filled or a new efficient boiler to be installed as a condition of the Building Regulations approval. This overall improvement would not be required just when an extension is built. It would apply whenever substantial work is to be carried out. The Approved Document suggests that an appropriate trigger is if the value of the work exceeds £8000 excluding vat. Unless the owner wishes to go further, the additional work should only include those measures that achieve a payback of less than seven years. A marginal cost cap of 10% limits the number of such measures that must be included.

As a separate category, if new dwellings are being created as a result of a change of use of an existing building, then the standard of the newly created dwelling should be as high as practicable.

At the last review, the concept of a replacement controlled service or fitting was introduced. Essentially this required that when boilers, hot water vessels or windows were replaced, they had to meet a defined performance standard.

With this review, the proposal is to extend the concept to include controlled elements, and to enhance the scope by not only including ‘the provision or extension’ of these controlled items, but their ‘alteration or renovation’ as well. This means that when any part of the building envelope or heating system is subject to substantial repair or replacement, then improvement should be made.

It will be appreciated that the cost of achieving a given improvement in energy efficiency is context dependent. For example, it is easier and cheaper to improve the U-value of an unfilled cavity wall than it is to achieve a similar improvement on a solid wall. Consequently, the level of improvement that might be reasonable in one dwelling may not be reasonable in another.

This consideration of context provides an important link with the requirements of the Energy Performance of Buildings Directive, that will begin to come into effect in January 2006. It will require that whenever a house is made available for sale or let, an energy performance certificate should be provided to the prospective purchaser or tenant. The certificate will be required to include a list of cost-effective improvements that could be made to the dwelling.

The certificate will be part of the Home Improvement Pack and similar provisions for dwellings offered for rent, and will have been prepared by trained assessors. This list provides the context that will enable building control to determine what is reasonable in the particular case.

Boilers and windows

In line with the government’s commitment in the Energy White Paper, the proposals require that from April 2005, the majority of all replacement boilers must meet a minimum SEDBUK rating of band B (ie the boiler must be condensing). It is difficult to accommodate condensing boilers in certain situations (eg where there are problems with plumes from flues or conveying condensate into a drain).

The circumstances that define these special situations are being developed in conjunction with the domestic heating industry, and will be the subject of periodic revision. In such situations reasonable provision would be a high efficiency non-condensing boiler. In all cases, a set of minimum control requirements would be expected.

In line with the general philosophy adopted for this review, the draft Approved Documents do not go into technical detail. It is proposed that this will be provided through a second tier of technical publications prepared by industry and the professions, and will also draw on established publications produced by the Housing Energy Efficiency Best Practice Programme.

Another important change in respect of replacement windows is the recognition of the Window Energy Rating Scheme (WERS). This will now provide one of the routes to demonstrate that the energy performance of the window is of an appropriate standard.

The importance of the WERS is that it recognises the passive solar benefit of glazing as well as the conduction heat loss. This means that windows with slimmer frames can have the same rating as a conventional window that has a better U-value.

For more information on the proposals for amending Part L of the Building Regulations and implementing the EPBD. Visit www.odpm.gov.uk/br/consult