Guidance on performing Part L1 (2006) assessments

The following workflow is recommended for preparing and performing a <VE> Compliance analysis for Part L1 (2006). The plan need not be followed slavishly. Variations can be made in the ordering of the tasks and experienced users may wish to take alternative approaches to some of the stages. The purpose of the plan is to guide you through the basic process.

The process usually begins with the entry of building geometry in ModelIT.

Constructions for building elements such as walls, roofs and glazing are created in the Constructions Database (CDB) utility accessible via Apache View or <VE> Compliance. They should satisfy the U value requirements of Criterion 2. The construction definition should include allowance for non-repeating thermal bridging, using an area-based thermal bridging coefficient. Constructions may be assigned to building elements in either Apache View or <VE> Compliance.

At this stage you may wish to go to <VE> Compliance and set up some of the high-level data required for the compliance analysis.

First check that the Regulatory framework selector is set to ‘Part L1 (2006) – ApacheSim’.

In the ‘Set Building and System Data’ button near the bottom of the screen select data specific to the SAP methodology. The SAP methodology also requires that the dwelling living area is specified for the zone(s) that make up the living room; this is done by selecting the zone(s) and using the room type selector to change the room type to Dwelling Living Area.

Each dwelling (apartment, house) must be analysed in separate <VE> Compliance assessments. The part of the building included in a particular analysis is defined by the settings of the check boxes ‘Include room in Building Regs analysis?’ for each dwelling on the Space Data Building Regulations tab.

When you are satisfied that the constructions and building and system data is applied correctly, click on the button ‘Compare Dwelling and Target emission rates using SAP 2005’. The software will immediately begin the analysis for compliance with Criterion 1.

The first stage of the analysis is a check on building element U values as required by Criterion 2. Any failures will result in a screen message and the analysis will halt.

The next step is the calculation of the actual and notional building. Progress is indicated on the screen.

Results from both dwellings, together with data provided on the Building & System Data dialogue, are then fed into the compliance calculator. The calculations performed there to produce the Dwelling CO₂ Emission Rate (DER) and Target CO₂ Emission Rate (TER) are shown later sections.

When the process is complete a summary of the result of the Part L1 analysis will be displayed on the Results tab, and you can click on a button to display the compliance documents generated by the <Virtual Environment>.

If the result is a pass for Criterion 1 you may move on to the next stage.

Otherwise you will need to improve the design and try again.

Click on the button labelled ‘Assess potential for summer overheating’. This performs the overheating analysis following the procedure outlined in Appendix P of the SAP methodology document.

At the end of the simulation a report is generated on the incidence of high temperatures in the dwelling, which can form part of your Part L1 submission.

Assuming a successful outcome, the Part L1 (2006) compliance process is now complete in relation to those aspects that can be tested before construction. The reports generated, together with appropriate supporting evidence, can now be submitted to Building Control.

The content of Part L submissions should be agreed in advance with the local Building Control officer as there may be differing interpretations during the early stages of implementation of the new regulations. These are likely to be resolved over time as a sufficient number of Competent Persons are trained and accredited. It may be necessary, for instance, to agree how compliance with Criterion 4 will be met post construction as part of the pre-Construction report.

The following measures should be considered when attempting to achieve a pass for the Dwelling CO₂ Emission Rate (Criterion 1). Many of them will also benefit summer temperatures (Criterion 3). They are listed in rough order of importance.

Substantial reductions in building emission rate can be achieved by improving Heating system efficiency.  The Domestic Heating, and Ventilation Compliance Guide defines requirements for a number of features. These are potentially onerous requirements that need to be taken into account from the start of projects. 

DHW systems should also be examined for efficiency opportunities.

Efficient lighting and lighting controls offer substantial potential for bringing down emission rates and moderating summer temperatures. Any saving in lighting consumption has a double benefit, directly reducing electrical load and by reducing room gains having a favourable effect on summertime cooling loads and temperatures. This can be augmented in the interface by introducing more energy efficient luminaires.

Reducing glazing area, introducing shading and optimising glazing type may all improve the chance of overheating. The implications for heating energy use and natural lighting, should, however be borne in mind.

Improving U-values will tend to reduce heating. Increasing the solar performance of the glass by reducing the solar gains into the building will reduce overheating but may also increase heating demand.

Reduction in thermal bridging will improve the chance of compliance. Using accredited construction details will reduce thermal bridging; the planning portal http://www.planningportal.gov.uk/ is to offer guidance on these accredited construction details.

The air permeability of the building envelope has to conform to the standard set by Criterion 2, namely a permeability of 10 m³/hr/m² at 50 Pa. There is further guidance in L1A as to the requirements for air permeability testing (paragraphs 54-63). The guidance indicates the number of dwellings that must be tested and also the alternative to pressure testing that is available for smaller developments.

Note: any increase in the air permeability (bought about by pressure test exemptions) will increase the DER.

The use of any renewable (PV and solar water heating have calculation methods in the SAP approach) will reduce the carbon emissions of the dwelling and will aid compliance.