Building standards technical handbook 2020: domestic

Within Scottish building regulations, improvements in energy standards have been made over many years including, in 2007, the move to a single carbon dioxide emissions based methodology for assessing carbon and energy performance in new buildings.

The Sullivan Report - in 2007, Scottish Ministers convened an expert panel to advise on the development of a low carbon building standards strategy to increase energy efficiency and reduce carbon emissions. This resulted in The Sullivan Report – ‘A Low Carbon Building Standards Strategy for Scotland’. A key recommendation of this Report was staged improvements in energy standards in 2010 and 2013, with the aim of net zero carbon buildings (emissions for space heating, hot water, lighting and ventilation) in 2016/17, if practical.

In May 2013 Scottish Ministers reconvened the Sullivan panel with a view to revisiting some of their original recommendations, taking account of the impact of the economic downturn on the construction sector. Whilst maintaining the level of ambition, the 2013 Update report recommended a more moderate pace of change and offered recommendations in three areas:

The Climate Change (Scotland) Act 2009 http://www.legislation.gov.uk/asp/2009/12/pdfs/asp_20090012_en.pdf creates a statutory framework for delivery of greenhouse gas emissions reductions in Scotland. The Act sets an interim target of a 42% reduction in emissions (compared to 1990) by 2020, and an 80% reduction target for 2050, with annual targets set in secondary legislation. The high level measures required in each sector to meet Scotland’s statutory climate change targets, for 2022 and in the long term, were set out in the Scottish Government’s Climate Change Delivery Plan. This includes recommendations for the delivery of low carbon new buildings.

The construction sector has a major role to play in this respect. Emissions from the burning of fossil fuels are contributing to climate change, with energy use in buildings a significant source of such emissions. Increased energy efficiency and promotion of renewable energy are therefore an important element of Scotland’s strategy to tackle climate change.

To deliver buildings that are more energy efficient and have fewer carbon dioxide emissions, a greater emphasis is needed on the overall effect that design and specification choices, construction and commissioning of new work can have on building performance.

The intention of Section 6 is to ensure that effective measures for the conservation of fuel and power are incorporated dwellings and buildings consisting of dwellings. In addition to limiting energy demand, by addressing the performance of the building fabric and fixed building services, a carbon dioxide emissions standard obliges a designer of new dwellings to consider building design in a holistic way.

Improvements set out within this section will result in a greater need to consider the benefits which localised or building-integrated low carbon equipment (LCE) (e.g. photovoltaics, solar water heating, combined heat and power and heat pumps) can make towards meeting standards. Although the focus is primarily on lowering carbon dioxide emissions from dwellings in use, the measures within this section are intended to reduce energy demand and continue to ensure that, for new homes and new building work, use of energy and fuel costs arising from this are both minimised.

Guidance also recognises issues relevant to requirements within Articles 3, 4, 6-9 & 11 of EU Directive 2010/31/EU on the Energy Performance of Buildings (EPBD) and Article 13 of the EU Directive 2009/28/EC on the promotion of the use of energy from renewable sources.

The standards and guidance given in this section are intended to achieve an improvement, for new homes reducing emissions by approximately 21% compared to the previous 2010 standards (45% compared to the 2007 standards). However, nothing here prevents a domestic building from being designed and constructed to be even more energy efficient or make greater use of low carbon equipment (LCE).

This section addresses the carbon dioxide emissions and energy performance of all domestic buildings (houses, flats and maisonettes) and ancillary buildings. In respect of dwellings, all parts of a building intended to form part of the dwelling should be within an insulation envelope.

This section should be read in conjunction with all the guidance to the Building (Scotland) Regulations 2004 but in particular Section 3: Environment has a close affiliation with energy efficiency, regarding:

Other than where qualified in the limitations to individual functional standards, the standards and guidance within this section apply, irrespective of the intended lifespan or the potential to relocate a building:

Heated stand-alone buildings - in 2007, the EU Directive 2002/91/EC on the energy performance of buildings led to the introduction of the category of ‘stand-alone building’, a definition of which is available in Appendix A of the Technical Handbooks. The Directive, now recast as Directive 2010/31/EU, exempts such buildings where less than 50m² in floor area, from both the need to use a methodology to calculate energy performance (Standard 6.1) and also the production of an Energy Performance Certificate (Standard 6.9). The defined term includes not only detached buildings, but also thermally divided parts of a buildings with separate heating shut-down control.

Stand-alone building that are less than 50m² in floor area must still comply with Standards 6.2 to 6.8 (6.10 not being applicable to domestic buildings). The guidance to Standard 6.2 recommends that the insulation envelope of such a building should achieve the level of performance applicable to an extension.

Examples - common examples of stand-alone domestic buildings that could be less than 50m² include: a heated stair enclosure associated with a block of flats; a heated summerhouse ancillary to a dwelling; and a conservatory attached to a new or existing dwelling.

Work on existing buildings - as for other standards within Scottish building regulations, the energy standards apply to conversions and also work on existing buildings, such as extensions, conservatories, alterations and replacement work. However, in some situations, individual standards may not apply or guidance on compliance with the standards may differ for such work. The latter is usually to recognise constraints that arise when working with existing buildings.

It is advisable, in the first instance, to check the functional standard as sometimes a limitation removes certain classes of this type of work. Where not excepted by a limitation to a standard, the provisions of the standard will apply in full to the new work on the existing building, other than where proposed works are wholly categorised as a conversion, where the standard in question may be met as far as is reasonably practicable. This is identified in the introduction to the guidance supporting each standard.

Thermal transmittance (U-value) is a measure of how much heat will pass through one square metre of a structure when the temperature on either side differs by one degree Celsius. It is expressed in units of watts per square metre per degree of temperature difference (W/m²K).

Measurements of U-values should be made in accordance with BS EN ISO 8990:1996 - ‘Thermal insulation. Determination of steady-state thermal transmission properties. Calibrated and guarded hot box’. In calculation, thermal bridging may be disregarded where the difference in thermal resistance between bridging and bridged material is less than 0.1m²K/W. For example, normal mortar joints need not be taken into account in calculations for brickwork, but should be taken into account for lightweight insulating blockwork.

Taking into account guidance from BRE publication BR 443:2006 ‘Conventions for U-value calculations’, http://www.bre.co.uk/filelibrary/pdf/rpts/br_443_(2006_edition).pdf individual U-values of building elements forming the insulation envelope can be established by a number of methods, including:

The thermal conductivity (the λ-value) of a material is a measure of the rate at which that material will transmit heat and is expressed in units of watts per metre per degree of temperature difference (W/mK). Establishing the thermal conductivity of materials in a building element forming part of the insulation envelope will enable the thermal transmittance of the element to be calculated.

Measurements of thermal conductivity should be made in accordance with BS EN 12664: 2001, BS EN 12667: 2001 or BS EN 12939: 2001. There are a wide range of technical publications which give the thermal conductivity of common construction materials but, where available, preference should be given to values that are certified by a notified body. Additional guidance given in BRE publication BR 443: 2006 should also be followed.

Previously, thermal transmittance through separating walls or separating floors between 2 dwellings or between a dwelling and other heated parts of the same building (e.g. between a flat and a protected zone with space heating) was not assessed. Accommodation on both sides of the separating element was expected to be at a similar temperature when the dwellings or buildings are occupied.

This is no longer always the case. Whilst ‘no loss’ may still be assumed for solid walls, research has identified previously unanticipated heat losses from air movement in cavity separating walls. This ‘thermal bypass’ is now identified in the calculation methodology and guidance to Standard 6.1 and in guidance to Standard 6.2.

If a dwelling or part of a building consisting of dwellings is separated from an unheated enclosed area, (for example solid waste storage accommodation, a porch, garage, protected zone or underground car park) the U-values of the walls/floors (including doors and translucent glazing) may be calculated by:

A roof of a dwelling or building consisting of dwellings that also performs the function of a floor or similar loadbearing surface (e.g. an access deck, escape route, roof garden or car park), should be considered as a roof for the purpose of assessment within this section.

A conservatory allows natural light and natural ventilation to be ‘borrowed’ through glazing and ventilators into adjacent rooms of a dwelling. In view of this, a large area of translucent material is required in the conservatory fabric to ensure that such rooms are not adversely affected. The definition of conservatory in Appendix A of the Technical Handbooks should be read in conjunction with the SAP 2012 document. Further guidance is given on how the standards apply to conservatories in clauses 6.1.7, 6.2.12 and 6.3.2.

In a dwelling with an atrium, it should be assumed that the atrium is to gain heat transfer from the surrounding building. The continuity of the insulation envelope occurs at the roof level (usually predominantly glazed with translucent material) and the atrium is considered to be a heated part of the dwelling.

Unless otherwise identified in text, guidance given in support of Standards 6.3 to 6.6 now refers directly to information contained within the Domestic Building Services Compliance Guide for Scotland http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/techbooks/techhandbooks/dbscgs . The document replicates guidance published in support of building standards elsewhere in the UK and supports standardisation of the specification and expected performance of fixed building services throughout the UK. The Guide also provides helpful supplementary information that may assist designers in the installation and commissioning of services to delivering optimum operating efficiency.

Additional information on the use of a range of low carbon equipment (LCE), such as solar thermal systems, photovoltaic panels and heat pumps, and application within building regulations can be found within the Low Carbon Equipment Guides on the Technical Pages of the Building Standards Division website.

When calculating areas for the purposes of this section and in addition to regulation 7, schedule 4, the following should be observed:

The 2015 edition of Section 6 incorporates a number of changes whilst retaining the existing methodology introduced in 2007. The majority of these changes relate to improvement in specified performance to deliver the intended 21% aggregate reduction in carbon dioxide emissions on the 2010 standards (45% when compared to 2007 standards). A full summary of changes can be found on the Technical Handbooks page of the Building Standards Division section of the Scottish Government website http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/publications/pubtech.

The key changes that have been made to the standards and guidance since 1 October 2013 include:

EU Directive 2009/28/EC http://europa.eu/legislation_summaries/energy/renewable_energy/en0009_en.htm - promotes the use of energy from renewable sources, including promotion within national legislation. It establishes a common framework for the use of energy from renewable sources in order to limit greenhouse gas emissions, including establishment of national action plans and targets which set the share of energy from renewable sources for 2020.

Scottish Ministers can, under Section 7 of the Building (Scotland) Act 2003, approve schemes for the certification of design or construction for compliance with the mandatory functional standards. Such schemes are approved on the basis that the procedures adopted by the scheme will take account of the need to co-ordinate the work of various designers and specialist contractors. Individuals approved to provide certification services under the scheme are assessed to ensure that they have the qualifications, skills and experience required to certify compliance for the work covered by the scope of the scheme. Checking procedures adopted by Approved Certifiers will deliver design or installation reliability in accordance with legislation.

The Certification of Design (Section 6 – Energy) for Domestic Buildings scheme has been approved by Scottish Ministers to confirm compliance with Section 6. Details area available on the certification pages of the Building Standards Division website http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/profinfo/cert.