Building Regulations Approved Document Part L2

Approved Document Part L: 2002 was split into two separate documents related to ‘dwellings’ and ‘non-dwellings’; the new Part L:2006 has been given further differentiation with the introduction of ‘new’ and ‘existing’ buildings, resulting in a permutation of four parts.

As described in some detail in the article predominantly about Approved Document L1, the opening ten pages or so of the new Approved Document L2 (7 pages in ADL2A; 11 pages in ADL2B) have been given over to Use of Guidance explanatory notes and interpretative guidance, which describe the Building Regulations revisions and subjects them to an examination of their compliance criteria. The documents also follow the format of ADL1 by emboldening key text (defined in the Appendix), and including italicised explanatory – or justificatory - text to clarify the motivation for certain new paragraphs.

The legalistic appearance of this opening section is meant to situate the Approved Documents in the real changes in the Regulatory framework that have been driven by the Energy Performance in Buildings Directive and the Secure and Sustainable Buildings Act. In some instances, you have to wade through all the section clauses to get to the substantial point. For instance:

“17D. – (1) Paragraph (2) applies to an existing building with a total useful floor area over 1000m² where the actual building work consists of or includes:
a. an extension
b. the initial provision of any fixed building services; or
c. an increase to the installed capacity of any fixed building services.
(2) Subject to paragraph (3), where this regulation applies, such work, if any, shall be carried out as is necessary to ensure that the building complies with the requirements of Part L of Schedule 1.
(3) Nothing in paragraph (2) requires work to be carried out if it is not technically, functionally and economically feasible.”

This final clause is interesting in as much as there may be scope for arguing that complying with the requirements of Part L would be economically unfeasible – and hence unreasonable. It is at the discretion of the Building Inspector to accept or repudiate this line of argument. In ADL2B, Table 1, there are some criteria relating to economic feasibility, but test cases are awaited with interest.

Secondary documents

In Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings, there are references to 26 other subsidiary documents, ranging from the BRE’s ‘Solar Shading of Buildings’, to the less well-known 'A Practical Guide to Ductwork Leakage' by the HVCA. A number of these documents, such as the CIBSE Guide A: 'Environmental Design' and its Technical Manual TM36 ‘Climate Change and the Indoor Environment: Impacts and Adaptation’ are only just released, others still await publication.

A key document is the updated Standard Assessment Procedure - which is essential for completing the fuel calculations, and includes factors such as solar, non-repeating thermal bridges, and fixed electric lighting. It is available through the BRE website (www.bre.co.uk/sap2005). NB: All documents referenced in the Approved Documents become Approved Documents in their own right.

Approved Document L2A relates to the construction of new buildings other than dwellings (use classes provided at the back of ADL1) as well as extensions to non-dwelling buildings where the ‘total useful floor area’ (that is the gross internal floor area up to the internal face of the external wall, see clause 104, page 28 [in ODPM version dated March 24th 2006]) of the extension is greater than 100m² AND greater than 25 percent of the total useful floor area of the existing building. Confusion on this issue has been clarified by Ted King of the Buildings Division of the ODPM.

However, if domestic and non-dwelling facilities are included under the same roof, then it falls under the requirements of L1 provided that the living accommodation occupies a ‘substantial proportion’ of the total area of the building. Once again, there is room for discretion here on behalf of the Building Control Body, and one local authority, say, may take a different view to another.

Temporary buildings with a ‘planned time of use’ of two years or less, are exempt, and some modular constructions are referred to the Modular and Portable Building Association’s guidance ‘Energy Performance Standards for Modular and Portable Buildings’.

BER not DER

As ADL1, there is only one calculation tool which is notionally the same as that for ADL1, in that a Target CO₂ Emission Rate is calculated on the basis of a notional building of the same proportions and typology to the proposed building, which is then compared to the actual building performance. The actual must equal or surpass the target. To differentiate between ADL1 and ADL2, the latter’s actual building performance is called the Building CO₂ Emission Rate (BER) whereas ADL1’s is called the Dwelling CO ₂ Emission Rte (DER). In the same way as ADL1, ADL2 includes limiting U-values that determine the maximum U-value permissible in any one area: this is used as a way of ensuring that improvements in the building overall do not lose sight of the need for consistency (in particular minimising condensation risk) across the whole envelope.

Under pressure

The subsidiary, or second tier document Measuring Air Permeability of Building Envelopes by the Air Tightness Testing and Measurement Association outlines the stringent testing regime required. It states that ‘the test procedure can be significantly affected by extremes of weather (wind speed, internal/external temperatures). Weather forecasts should be obtained prior to the proposed test date and if inclement weather is predicted, re-scheduling may be necessary.’ If this predictive cost can’t be borne, then a higher value corrective can be factored in. For buildings up to 500m² total useful floor area, air pressure tests can be avoided if the air permeability is raised to a notional 15m³/hr.m² in the BER calculations.

Where buildings fail air pressure tests, there is a period of grace in the new ADL’s up to 31st October 2007 whereby corrective remedial works need be undertaken – but set at a lower standard – before retesting. If an improvement of 75percent can be shown to have been made between the initial test and the design air permeability (or similar), then it will be deemed to satisfy.

A section on commissioning and operations includes details on preventing air leakage from ductwork and the need for building log book to ensure that the user is aware of, and takes advantage of, the efficiencies in the system. As with ADL1, a checklist is included in the back to track the compliance through various stages of a job

Clarification of relevant works

In ADL2B: Conservation of Fuel and Power in Existing Buildings Other Than Dwellings, relates to the erection or extension of a building, but also to underpinning, inserting insulation into a cavity or any work where it is deemed that it shall materially affect a building in such a way that it results in ‘not complying with relevant requirement where previously it did’. So improving a building’s U-values by inserting cavity insulation will draw down the full might of the requirements of the Approved Documentation. Simply ‘improving’ is no longer sufficient, it must ‘comply’ incurring potential knock on effects and costs. The self-certification schemes and exemptions are an attempt to mitigate such incursions into well-intentioned upgrades, but – in a similar way to ADL1B – create a bureaucratic framework that might actually dissuade clients from improving their facilities. Replacing a socket does not, you’ll be pleased to hear, require a building notice or the deposit of full plans to the Building Control Body. Putting a new socket (not a replacement) in a kitchen, does, and is referenced in Approved Document P as well as ADL2B.

The calculation conventions in ADL2B are as ADL2A. However, the ATTMA second tier document on pressure testing (see above) stipulates that where an extension is less than 1000m2 and less than 25percent of the useable floor area of the existing building that is being extended, then air pressure tests are not required. Over these size limits, the extension is deemed to be a new building and the requirements of ADL1 apply.