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Building Regulations Approved Document Part L

1 December 2010 No Comment

Approved Document L of the Building Regulations has undergone a major revision, which is a step on the governments stated trajectory to zero carbon. The design, assessment and on site construction of building details is one of the main areas of focus as these can contribute significantly towards the overall heat losses through the building envelope.

How will the design and modelling of a building detail affect the SBEM calculation?

The Part L2A document sets out 3 levels of building detail certification and the associated penalties which must be applied to the calculated psi values or linear thermal bridging associated with the calculated detail in the BER calculation.

  1. A quality assured approach (checking by an approved independent third party) to enable the calculations to be used directly.
  2. Unchecked calculations by a person with suitable expertise using the methods set out in BRE Convention BR497. In this case the calculated values should be increased by 0.02 W/mK or 25%, whichever is the greater.
  3. Unaccredited details with no linear transmittance calculations carried out. For these, the generic values given in the BRE Information Paper IP1/06 should be increased by 0.04 W/mK or 50%, whichever is greater.

It’s possible to use a combination of building details from the 3 levels, in which case the psi value and associated penalty for each detail is used.

How do I ensure I minimise the total calculated heat loss and penalties from the building details?

The use of unaccredited details with no calculated values should be avoided at all cost. The generic values quoted in IP1/06 are much higher than those which can be obtained by careful  design and modeling. In addition a further 50% penalty must be added. Use of unaccredited building details can increase the calculated CO2 emissions by as much as 10%, dependant upon the building type, making compliance much more difficult.

Specifying calculated or independently assessed building details from a reputable cladding system manufacturer, will minimise heat loss through thermal bridging.

While “independently assessed details” will provide a 25% better performance than “calculated details”, the overall effect on the calculated building CO2 emission is only around 1% dependant upon the building type.
Tata Steel supply chain partners are all able to provide bespoke building details which have had the associated psi values calculated by an experienced person.

It is essential to ensure that the building detail is installed as designed, otherwise the calculated psi value will not be achieved and the values from IP1/06 plus a 50% penalty will apply. This could result in the “as built” building not achieving the target CO2 emission rate and not complying with Building Regulations.

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