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CPD: Approved Document L2A

The full title of this CPD is ‘Building Regulations Part L 2010: thermal, solar and air permeability requirements for windows, doors and curtain walling - specialist unit for new build, non-dwellings’, and it is sponsored by Sapa Building System

Previously known as Glostal, Sapa started in 1963 and is one of Europe’s largest suppliers of aluminium building systems, with a turnover of over £3.2 billion. Sapa manufactures curtain walling, windows, doors, glazed roof systems, solar control systems, photovoltaic systems and specialist blast and fire-resistant facades.

Part 1: Environmental context

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Over time, Approved Document L has expanded in response to environmental concerns. It now encompasses a wide range of energy uses in buildings.

The previous government enhanced targets for reduced CO2 emissions by 80 per cent based on 1990 emissions to be achieved by 2050. In addition to the pre-existing 30 per cent reduction target by 2020, the current coalition has introduced a further target of a reduction in emissions of 50 per cent by 2027.

Further ambitions include a timetable for all new build projects to become zero carbon. This is led by schools in 2016, 2018 for other public buildings and 2019 for all other non- domestic buildings.

This focus on the construction industry is hardly surprising, given that about 50 per cent of the uK’s energy consumption is construction and building usage related.

Part 2: The regulations 1

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Generally, all new non-dwellings should be built to ADL2A, as should large extensions, also instigating a requirement for consequential improvements under Regulation 17D. Non-dwellings include schools, libraries, offices, sports facilities and retail outlets, but also, less obviously, rooms for residential purposes, for example, nursing homes and student accommodation.

As Paragraph 1.11 of Approved Document ADL2A points out, responsibility for compliance with the Building Regulations rests with the person ‘carrying out the building work’. This could be the designer, the builder, the installer or even the building owner, who could be served with an enforcement notice in cases of non-compliance.

Following the Approved Documents is only one way of complying with the Building Regulations and you have the option to demonstrate compliance in other ways if you can convince Building Control.

Part 3: The regulations 2

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Key to achieving emission compliance are three ‘buildings’, the first two of which are theoretical. 1. A notional building generates the ‘Target Emission Rate’ (TER) - this determines the calculated maximum permitted CO2 emissions for the project building. The calculation includes reference U-values, Psi-values and air permeability. The guidance document is the National Calculation Methodology.

2. The Reference building is a theoretical building of the same size, shape, orientation and zoning as the actual building. This ‘building’ is used as the basis for determining the Energy Performance Certificate.

3. The ‘Building Emission Rate’ (BER) is the predicted CO2 emissions from the completed building. This includes the actual U-values of installed components.
To achieve compliance, the BER must not exceed the TER. In addition, ADL2A sets limits on solar gain and permeability.

Part 4: Thermal requirements 1

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ADL2A introduces a definition for display glazing. This includes doors within display glazing. High-usage entrance doors should be either automatically opening or of robust construction, the latter having some form of door closing mechanism.

The U-values for display glazing, high- usage entrance doors and windows (including curtain walling) are considered separately. Current regulations require adherence to limiting U-values. However, because the notional values used to calculate the TER are so much better than the maximum permitted U-values, using these ‘backstop’ values will almost certainly mean that the BER exceeds the TER.

Part 5: Thermal requirements 2

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Paragraph 4.29 of ADL2A notes that, by using the maximum permitted U-values (referred to as ‘fabric limiting parameters’) for each component, the design will almost certainly fail to meet the required overall TER.

A better guide might be, initially, to use those figures applied in calculating the TER. From there, depending on designed air permeability, building usage and shape, figures might be relaxed. The challenge for the design team is to ensure a balance between the thermal performance of all components, including associated Psi-values. Achieving this balance often means that the resultant build can be more cost-effective than if standard, ‘off the shelf ’ performance figures are applied across the building envelope.

Part 6: Solar gain 1

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Criterion 3 requirements apply to buildings which are naturally and mechanically ventilated or even air-conditioned, removing a previous anomaly which inadvertently discouraged natural ventilation. Dynamic software modelling shows that it is now easier to design large glass facades with solar shading that comply with ADL2A.

ADL2A provides a methodology for vertical glazing design, requiring that a building’s solar gain be no worse than the aggregate notional value from an east-facing facade with full width, 1m-high glazing with a G-value of 0.68, from April to September. This G-value, the effective solar shading value, where 1 is no shading and 0 is total shading, can be achieved by natural shading, solar control glass, solar films, overhangs, fixed or adjustable shading and integrated photovoltaic panels.

Part 7: Solar gain 2

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Although solar gain is often simplified as being beneficial in the winter and adverse in the summer, studies undertaken by Faber Maunsell on behalf of BRE demonstrate that the reality is more complex. It is now recognised that the main challenge is for building designs to achieve efficient energy management, balanced by the requirement to ensure adequate daylight.

Shading, ventilation and thermal mass all contribute significantly to managing solar gain. Computerised solar shading predictive tools, used to design the optimum solar solutions, help. Often the results may show a requirement for different solar control solutions across different facades.
Whatever solution is applied as part of the building design, the ability to maximise energy efficiency across all four seasons is now considered the most efficient, and often the most cost-effective, long-term solution.

Part 8: Air permeability

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ADL2A demands compulsory air permeability testing under certain criteria. While base values for air permeability remain at 10m3/h/m2 at 50Pa, in order to achieve acceptable CO2 emissions, lower permeability is almost certainly necessary. As a comparison, the Passivhaus standard is typically 0.6m3/h/ m2. Modern products undergo stringent air and water permeability testing, often using aero engines, so tend not to be a problem. The biggest challenge for any designer is ensuring continuity of pressure barriers, often at interfaces with other building materials, and in communicating these barriers to the construction team.

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