Part L 1A & 1B – Building Regulations 2006 

Part L of the building regulations changed on the 3 April 2006, the motive for this change is the reduction of carbon dioxide (CO2). Part L1a, which covers domestic new builds, has the intention of reducing CO2 emissions by 20 per cent over the current building standard. This is an ambitious target but is achievable.

As compliance revolves around actual emissions the method of showing compliance has been changed, the carbon index, target and elemental methods are no longer valid. The only allowable method is now based on the Standard Assessment Procedure 2005 (SAP2005). This calculation assesses actual CO2 emissions from a property taking account of insulation, heating system, ventilation and lighting. 

Part L1a - Five step compliance

Step 1: Predicted CO2 should be no greater than target emissions

DER (Dwellings emission rate) < TER (Target emission rate).

Step 2: Check performance is no worse than minimum standards

Step 3: Check no excessive summer overheating

Step 4: Check actual construction performance complies with Part L- includes pressure testing and recalculation of DER if required.

Step 5: Provide efficient operation and maintenance instructions including making the data available to produce Energy Performance Certificate. 

All of these steps require the competent use of the SAP calculation. The importance of making sure this calculation is being applied correctly cannot be stressed enough. An error made at the start of the process will be likely picked up at step, 4 or 5, which could prove costly for the developer. Only authorised SAP assessors may produce the EPC but in reality they are the only group that can be relied upon to provide these calculations at every stage. It would be a false economy to use an unauthorised person to produce the SAP calculations at step 1 when an authorised assessor will have to be used at step 5. 

The SAP rating is an indication of the cost of running the property and it is used only to inform potential purchasers how efficient a property is. Current legislation requires that the SAP rating is displayed in all new build properties prior to sale and this piece of legislation will continue until the EU energy performance of buildings directive is enacted. This legislation requires all purchasers or tenants to receive an energy performance certificate (EPC) prior to agreeing to any purchase or tenancy. The Home Information Pack (HIP) for new build will require the EPC and this should be enforced June 2007.

SAP2005 also produces the CO2 emissions of a property and it is this which is used to show compliance with Part L1a 2006. The methodology is fairly straight forward, first a target emission rate (TER) is calculated, this is the CO2 from a notional gas heated dwelling of the same size and shape as the actual, in addition the heat losses are based on the elemental u-values found in Part L2002. The notional house emissions are then adjusted depending on fuel being used in the actual and reduced (improved) by a factor of 20 per cent. The TER is then compared with the actual dwellings emission rate (DER).

The use of the DER allows real flexibility in the design but there are still some constraints maximum permitted u-values, minimum heating system efficiencies, use of low energy lighting and air leakage.