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Strategy behind the revised Building Regulations Parts L1 and L2

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When the then construction minister Nick Raynsford launched a review of Part L in February 1998, his aim was to obtain the best possible contribution from the Building Regulations towards achieving our emissions targets for carbon dioxide. However, he cautioned that the contribution would be limited by the constraints of: conforming with our Better Regulation Policy; continuing to provide sufficient flexibility for designers; and, avoiding unacceptable risks.

The Building Regulations review is only one element in our overall Climate Change Programme - now administered by the Department for Environment, Food and Rural Affairs (DEFRA) - which sets out how the UK will meet its targets under the Kyoto Protocol for reducing greenhouse gas emissions, and for achieving the domestic goal to cut carbon-dioxide emissions by 20 per cent by 2010, a New Labour pledge in its 1997 election manifesto.

Since then, government has begun procedures to ratify the protocol, meaning that the UK will be legally bound to deliver the target of a 12.5 per cent reduction in emissions of the basket of six greenhouse gases by 200812. European Union member states are aiming to bring the protocol into force in time for the World Summit on Sustainable Development in Johannesburg in August.

Carbon dioxide makes up 80 per cent of the UK's greenhouse gas emissions and half of this comes from buildings - 30 per cent from dwellings and 20 per cent from other buildings. It is easy to see why improving performance standards is a prime goal.

Our Climate Change Programme was published in November 2000 following wide consultation. Within this programme, the changes to the Building Regulations are expected to deliver a saving of around 1.4 million tonnes of carbon per year in 2010 - about 8 per cent of the total called for.

There are also other important objectives.

The changes to Part L are also contributing to our policies of sustainable construction - administered by the Department of Trade and Industry (DTI) since changes in the machinery of government last year.We want to make buildings more effective at providing accommodation with economical use of energy but not at the expense of delivering satisfactory living and working environments.

The government also wants to encourage those responsible for the procurement and construction of buildings to take more responsibility for self-certifying compliance with the Building Regulations. We have consulted twice on proposals for Competent Persons schemes and this work bore its first fruit in the amendments made in March.

The government has been encouraging the construction industry, its clients and energy activists, to participate at every stage of the review process. Part of this participation aim is to encourage construction interests to prepare for future changes that pursuit of the Climate Change and Sustainable Construction policies will inevitably demand. To this end we published ideas in the June 2000 consultation on what minimum energy performance standards might be introduced around 2008. It is our intention to update this forecast from time to time.

The main changes Firstly, the definition of building work has been widened to reach more types of renovation and refurbishment of existing stock.

Replacement of windows and building-services systems is now covered, within certain limits, regardless of whether conventional building work affecting structural stability, resistance to fire and means of escape and access for the disabled is being undertaken.

Secondly, there is now guidance on testing buildings to confirm that 'as-built' performance reasonably matches the approved designs and hence that compliance has been achieved.

Thirdly, the scope of the technical requirements has been extended to address the provision of information that shows how the building and its building services can be operated and maintained effectively for the purposes of conserving fuel and power.

Fourthly, the basis in the Approved Document of showing compliance with Part L has been changed from achieving energy efficiency to controlling carbon emissions.

The main reason for this is to tie in with other government initiatives within the overall Climate Change Programme. The annual carbon accounting methods now offered enable the benefits of combined heat and power, district heating, photo-voltaic generation and other low-carbon and nocarbon energy sourcing to be taken into account. These new methods go handin-hand with the government's other policies of encouraging the take-up of alternative lower-carbon and renewable energy supplies.

The wider agenda Last year, DEFRA consulted on the draft European Directive on improving the energy performance of building energy performance. As a result, we pushed for a number of revisions which were agreed upon in the text accepted by the Energy Council on 4 December 2001. The European Parliament made suggestions for more than 30 amendments. These are presently being negotiated but the aim of the Commission and the current presidency is for the new directive to be adopted by the end of June 2002. Member states will have three years to implement the majority of the Articles, with the exception of the three main ones, for which implementation dates are still being negotiated.

The main purpose of the proposed directive is to promote improvement in the energy performance of buildings across European Union countries. It covers requirements regarding the setting of minimum standards for new and existing buildings, the use of energy-performance certificates whenever buildings are constructed, sold or rented, and regular inspections of boilers and air-conditioning units. It should also give a boost to renewables and CHP as well as to energy auditing.

It seems unlikely that the energy performance standards for building work in Part L will need to be revised in the short term as a result. But the Directive will introduce performance standards for energy use in buildings that are new for us.

It is unclear how the Building Regulations might need to change to promulgate these new usage requirements. But, in the next few years, we will need to consider what further improvements in fabric and engineering-services insulation are justifiable, and what alternatives to thermographic testing are, or could be, available for checking as-built condition.

More recently, we have seen the No 10 Policy Innovation Unit's Energy Review to government, which looks to Building Regulations having new roles to play in encouraging take-up of low-carbon and no-carbon technologies, and generally improving the performance of new and existing buildings.

Economists are developing a consensus on what price must be paid for emitting carbon (perhaps up to £140 per tonne per annum) and hence what is considered to be economic investment in energy-saving measures for buildings.

Acceptable costs In our Regulatory Impact Assessment we estimated that the changes would cause first costs to rise by up to £1,600 for dwellings (dependent upon type and size), about £5 per m 2for air-conditioned buildings and about £10 per m 2for naturally ventilated buildings. That represents something less than 2 per cent for most buildings.

The government, supported by most of those consulted, believes these extra costs are an acceptable consequence of seeking to achieve our carbon dioxide emissions targets.

Ted King has been responsible at the Department of Transport, Local Government and Regions (DTLR) for both the 1995 and 2002 Building Regulations, Part L concerning fuel and power ship. Without these, however, all those systems should achieve U values of 0.25 W/m 2K.For those new to this technology, there is now substantial guidance available on the design and use of closed-cell foam insulation panels, in a publication produced in association with Huntsman Polyurethanes.

This covers panel manufacture, building physics and design examples.

On flat roofs, typical insulation thicknesses for a U-value of 0.25 W/m 2K vary from 85mm for PUR/PIR to 150mm for rock mineral-fibre. The weight advantages of PUR/PIR may have implications for the building structure. Newer systems include membrane-faced insulated panels with profiled metal liners which provide simply installed prefabricated units.

Back to the wall As with roofs, there is an array of options for walls to achieve a U-value of 0.35 W/m l Full-fill cavity batts typically comprise 80mm-thick glass mineral fibre. It is important during installation to eliminate defects that could lead to ingress of moisture.

Full-fill injected insulant is typically 55mm PUR, 85mm of rock mineral fibre or 90mm for glass mineral fibre. There can be problems ensuring full insulation continuity, particularly with blown mineral fibre.

Partial cavity fill can vary from 35mm for phenolic to 75mm of glass mineral fibre.

Internally insulated dry lining can vary from 40mm for phenolic to 70mm of glass/rock mineral fibre.

External insulation can be used to ensure that the structure is warm and hence to take advantage of the thermal mass of the building fabric to regulate the temperature of the building. Insulant is generally phenolic, rock mineral fibre, expanded polystyrene (EPS) or extruded polystyrene (XPS).

With framed walls, the insulant is generally installed between the frames. Thickness varies between 50mm of phenolic and 115mm of glass mineral wool. Newer systems include 90mm of spray-applied rigid polyurethane (PUR). The new regulations will encourage greater use of prefabricated foam insulated panel systems. These have the added benefits of reducing time on site, ensuring continuity of insulation, and providing inherently airtight assemblies.

Stressed-skin panel systems vary in thickness from 208mm-thick OSB-faced panels to 261mm-thick cementitious-faced panels.

As far as air leakage is concerned, mineralfibre insulants offer little resistance and as such will not provide effective continuity of air barriers. Rigid board insulants are impermeable to air and can provide an envelope 'air barrier'. Spray-applied and canister-applied PUR insulants are effective gap sealing products for air barriers. From this survey we can draw a number of conclusions:

Theoretical thermal standards have not traditionally been achieved on site because of a combination of poor workmanship and/or inadequate design/specification.

The amendments to Parts L1 and L2 will address this issue through amended U-value calculation procedures and the introduction of testing, including thermographic testing for continuity of the installation.

There is a wide variety of insulation solutions that satisfy the regulation requirements, each with its own advantages and disadvantages.

Rigid closed-cell foam insulants are significantly thinner than glass or rock mineral wool insulants for any specific thermal resistance requirements.

Prefabrication of envelope assemblies removes the site potential for defects which cause poor thermal performance.

Stuart Borland works for Building Sciences

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