Take me to your designer

A golden opportunity to promote energy efficient systems? Or simply too little, too late? Tanya Ross, associate at Buro Happold Consulting Engineers, looks at the revision of Part L of the Building Regulations issued by the DETR.

The Millenium Sainsbury's in Greenwich: a role model environmentally friendly building using renewable energy supplies

The Millenium Sainsbury's in Greenwich: a role model environmentally friendly building using renewable energy supplies

Part L of the Building Regulations (Conservation of Heat and Power) is up for revision. Some might say about time, as this is the only major piece of legislature control impacting energy usage in new buildings. Indeed some have already said 'too little, too late', but this is the tool that the Government believes can contribute to significant carbon savings - up to 1.32MtC by 2010 - so it is scheduled to be a key factor in the struggle to meet emission reduction targets.

Since the Regulations affect all types of construction, it is important that changes are introduced after due consideration and consultation. By inviting comment from interested parties (ranging from the Construction Industry Council to the interested self-builder), the Department of the Environment, Transport and the Regions (DETR) is trying to ensure that industry can readily comply with the document. The intention is not to water down the proposed tightening of the Regulations, but to provide a chance to comment on the detail and the timetable for introduction.

The deadline for comment has now passed, and it is the unenviable task of the team to evaluate the feedback and decide upon implementation whilst still meeting the April 1 date for publication of the new legislation.

The consultation document is comprehensive, running to over 200 pages, but the key points can be summarised here.

For all buildings:

  • the Regulations are to be applied more widely to make energy efficiency requirements applicable to alteration and refurbishment work;
  • building fabric insulation standards improved;
  • new rules regarding air-tightness of buildings; and
  • specific attention given to detail design and site workmanship to avoid 'cold bridging'.

    For non-dwellings:

  • new guidance to avoid solar over-heating;
  • performance standards for boiler efficiency, heating and hot water systems;
  • performance standards for light fittings including display lamps;
  • alternative calculations to demonstrate efficiency of air-conditioned or mechanically ventilated buildings, using a Carbon Performance Index (CPI);
  • requirements for commissioning systems and checking that 'as-built' performance matches approved design;
  • obligations to provide energy meters; and
  • introduction of building log books.

    And for dwellings:

  • introduction of performance standards for lighting and lighting controls;
  • requirements for properly setting up heating, ventilation and hot water systems; and
  • suitable maintenance instructions to be provided to allow owners to operate systems efficiently.

    There is debate about whether the regulations should be split into separate documents covering dwellings and non-dwellings. It is calculated that dwellings would account for 58 per cent of the carbon savings mooted if all the requirements are introduced as scheduled, making the domestic market the major target for achieving change.

    Phased introduction
    There is also debate about the timing of the legislation. Current proposals are for a two-phase approach: an initial implementation six months after the new regulations are published and a further tightening of regulations 18 months after publication.

    Certain sectors of the industry believe that such an approach is confusing and open to misinterpretation, so it will be interesting to see if this recommendation remains when the document is finally published.

    So what will the practical impact be on designers trying to achieve sustainable architecture? The widening of the 'material alteration' definition will mean, for example, that replacement windows will be required to conform to the new 'U' value standards (1.8-2.2 W/m2K). This is intended to encourage the use of low-e rather than plain glass, although it is acknowledged that these values may not be appropriate in certain conservation instances. In addition, there are specific requirements controlling the addition of conservatories to dwellings, such that the conservatory either has to perform as well as the external fabric replaced, OR separation between house and conservatory is maintained (by the use of well-detailed, double-glazed doors, for example). Any extension and refurbishment that affects the building fabric - in both domestic and commercial instances - will need to comply with the more onerous requirements.

    U-turn on materials
    Improved 'U' values can only be a good thing. The impact on construction is likely to be expressed in several ways. Firstly, there is the obvious potential for thicker building envelopes as insulation thicknesses are increased. Tables have been drawn up to give required thicknesses for any given conductivity, with allowable reductions for certain building elements, although the range of constructions described is necessarily limited.

    Timber framing allows greater reductions and has led to concerns within the housebuilding industry that masonry construction will prove uneconomic given the new 'U' values. Manufacturers and suppliers of blocks, insulation and cladding materials will be required to provide better performance from their products, necessitating research and development into these materials. For windows and rooflights, where a 'U' value of 2.0W/m2K is expected, triple glazing will become a more feasible option on thermal as well as noise-reduction grounds, with specialist low-emissivity glass-types used because they meet the new standards.

    Improved air-tightness addresses the Achilles heel of well-intentioned low-energy designs. All the effort that goes into energy conservation measures is pointless without restricting uncontrolled losses through the building's fabric. Designers will be required to demonstrate that the structure meets the Air Leakage Index target of 10m3/h/m2 at an applied pressure of 50Pa.

    Testing for air-tightness is a straightforward exercise, although designers will need to make suitable provisions for blanking plates. Building Control will be given powers under the new legislation to determine if compliance is achieved, and to enforce remedial measures if tests are not passed (with a transition period for 'improvement' allowed). Reference is made to the importance of site workmanship and avoiding thermal bridging, encouraging good practice in design detailing - a government-backed publication of 'robust standard details' is imminent - and assisting in raising standards of cladding construction.

    Compliance with this section of the Regulations may be achieved through testing or through self-certification, whereby a 'competent person' confirms that appropriate fixing techniques and design details have been used. It is difficult to see at this stage how improved site workmanship can be enforced without requiring limitless resources from the Building Control Bodies.

    Hot air over heating
    For non-domestic buildings, the guidance on solar over-heating is designed to discourage reliance on mechanical cooling systems, by giving sensible guidelines on how summertime over-heating can otherwise be avoided by prudent use of shading, orientation, thermal mass, night cooling and the like. It is the first time the regulations have directly addressed energy usage for cooling, and for the energy-efficient designer, it presents a golden opportunity to promote the use of alternative passive systems to a wider range of clients.

    New standards for minimum boiler efficiency will require designers to select an inherently efficient unit and fuel source or to carry out lengthy calculations to prove compliance of less energy-efficient units. For example, a coal-fired boiler will not meet the required standards set down (expressed as a maximum carbon intensity - the carbon emitted per useful kWh of heat output). The proposals allow some 'trade-off' between system efficiencies and fabric performance - a more efficient boiler selection can lead to a slight relaxation of the minimum 'U' values - although this proposal has not been welcomed by conscientious designers, who point out that while heating systems are often replaced, building fabric is not.

    Lighting strikes
    The performance standards for light fittings will require selection of at least some low-energy fittings - fancy tungsten halogens are not eliminated, but their use is to be limited to localised areas - with a calculation required to show lighting averages less than 40 luminaire-lumens per circuit-watt. This should lead to the availability of more interesting designs for efficient light sources as manufacturers seek to promote their luminaires as truly green. Guidance on lighting controls is also introduced, advising a minimum distance of eight metres from a local switch to the luminaire it controls.

    The introduction of the Carbon Performance Index (CPI) method of measurement for air-conditioned or mechanically ventilated buildings brings a whole new raft of calculations to the building services engineer's fingertips. No doubt these will shortly be launched as add-ons to software packages. The implication on designs, however, is not readily predictable. Theoretically, it should give the engineer wider freedom to suggest solutions to clients by giving alternative means of demonstrating compliance, and by enabling unusual buildings to be assessed as a whole, taking into account useful heat gains and overall performance.

    In practice, it will take some time for engineers to become familiar with the new methods, and longer still to develop a feel for what all the figures mean. However, linking efficiency of mechanical systems directly to carbon emissions should give a more transparent comparison of the various options.

    Awash with paper
    The new requirements for energy meters and building log-books will no doubt lead to further scrambles towards the end of construction projects as contractors struggle to collate as-built information, yet their introduction is crucial if building owners and operators are to have a chance to monitor energy consumption and thus be alerted to poor performance. The exact benchmark to be set for comparison is a matter of some debate, and mandatory reporting is not planned until a later stage, but the introduction of these devices now will make crucial feedback available sooner rather than later.

    The Government has calculated that the impact on cost could be up to £1,400 per dwelling or £7/m2 for non-domestic buildings. This may cause a sharp intake of breath, but when compared to annual running cost savings of 25% - not including the impact of the Climate Change Levy - it is clear that the benefits quickly outweigh the costs.

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