A Summary of Part L1 A of the Building Regulations for New Build Dwellings

The Changes - Part L1A of the Building Regulations deals both with matters relating to the energy efficiency of new dwellings and the theoretical carbon dioxide emissions.

Revised guidance was published in Approved Document Part L1A 2013 and came into force for new build dwellings where the Building Regulation application was submitted, on or after 6 April 2014. This updates the previous guidance, which became effective in October 2010.

As expected, the changes are more onerous then the previous requirements. There are two main changes. The first is a reduction of 6% in the theoretical carbon dioxide emissions across the build mix, as compared to the 2010 requirements.  This affects the previous Dwelling Emission Rate/Target Emission Rate (DER/TER).  The 6% above is an average, and the amendments are slightly tougher for semi-detached and detached houses than they will be for flats and terraced houses.

The other major change is the introduction of a Fabric Energy Efficiency Standard. This new measure makes sure that the heat loss from the fabric of the building is minimised by the provision of a good level of thermal insulation from the outset. this closes a loophole in the DER/TER calculation. Once the Dwelling Fabric Energy Efficiency is achieved, then any excess carbon dioxide emissions to meet the DER/TER calculation can be dealt with by conventional low and zero carbon technologies or other products.

For both the Fabric Energy Efficiency(FEE) requirement and The DER/TER calculation a theoretical 'notional' dwelling of exactly the same size and shape is compared with the proposed dwelling. The Target FEE and TER are calculated by using the assumptions for the 'notional' outlined within Table 4 of Approved Document L1A(2013).

It is the DER/TER requirement which is generally more difficult to achieve and the reality is that, although there is some flexibility, the assumptions for the 'notional' calculations must be fairly closely followed. In particular the heat loss associated with lintels and to a lesser extent the heat loss at gable ends where there is insulation at ceiling level will both have a significant effect.

With very well insulated dwellings. 25% or more of the overall heat loss can be via the junctions between thermal elements and also around the perimeter of doors and windows etc. The relative heat losses become greater the more highly insulated the dwelling becomes.

There are a number of Approved Design Details which can be used but whichever specific details are used, they must be nominated 'up front'.

The greater the number of heat loss junctions which have to be taken into account means that a satisfactory DER in particular, will be more difficult to achieve. Put simply, standard 'boxes' work reasonably well, but fancy designs may prove more difficult to achieve.

The main problem is the implementation on site. Builders will not only have to build in accordance with them, but on completion, written confirmation WILL be required that he relevant nominated details were used.

There's no rocket science involved in their use, just a greater attention to detail than many builders are used to.

Our very strong recommendation is that for openings in external walls, either two separate lintels are used (one for the inner leaf and one for the outer leaf together with an insulated cavity closer all the way around the opening following the Energy Savings Trust Enhanced Construction Details). This is achievable with care but brings problems with ensuring the two lintels are exactly the same level and also in taking account of the rotation which may occur where an 'L' shaped steel lintel is used for the outer leaf, OR  proprietary composite 'one piece' lintels which avoid most of the cold bridging effect associated with standard steel lintels. They MAY be more expensive than a normal steel lintel, but it's a simple solution as they closely match the assumptions for lintels in the 'notional' dwelling, which other one piece lintels, by themselves, do not. In addition, there will probably be knock-on savings to be had elsewhere in the construction.

Cavity separating walls need to have a full fill insulation installed and the perimeter of the wall be sealed in an approved way to prevent convection currents being set up which significantly increase heat loss. Where there are cavity separating walls between dwellings, the guidance on filling and sealing the cavities as detailed in the MIMA publication must be followed. http://www.mima.info/pdf/MIMA-Party-Walll-Bypass-Guide.pdf (there is no mis-print in the spelling of wall - otherwise you will be taken to an earlier version).  This link may be broken - if you want a PDF copy please contact us.

You will need to check that the MIMA details are compatible with Part E Robust Details constructions (if you are registering with Robust Details Ltd). The details are compatible with most Robust Details, but there are a few anomalies.

If the separating wall design does not conform to a standard type, the Building Control Officer will need to confirm in writing both the acceptability of the form of construction and the U value he is prepared to accept (See approved Document L1A Table 3 for guidance). This poses particular problems where a new end of terrace unit is being built on the end of an existing terrace.

Please read the planning conditions carefully as there may be requirements for either low or zero carbon technologies or renewable energy sources.