Approved Document L1A - Compliance When Designing New Dwellings
Approved Document L1A 
provides guidance on complying with the requirements of Regulation L1 dealing with the conservation of fuel and power. It is one of four Part L Approved Documents.
Here the energy performance standards required for new dwellings is explained but this does not include buildings containing 'rooms for residential purposes' such as nursing homes and student accommodation or the common parts of apartment blocks which are outside the scope of L1A . For these categories document L2A is the appropriate reference.
Only one method of compliance
Unlike previous versions of Part L, there is now only one method of demonstrating compliance with the energy efficiency requirements and this is mainly based around carbon dioxide emission rates as calculated using the current version of the 'Standard Assessment Procedure' (SAP 2005).
For government approved calculation methodologies - visit the planning portal
SAP 2005 and carbon dioxide emissions
Under L1A , all dwellings must be designed and built such that their Dwelling Carbon Dioxide Emission Rate (DER) measured in kg of CO² produced annually per m² floor area is no worse than a defined Target Carbon Dioxide Emission Rate (TER).
The TER is based on a notional building of the same shape and size. SAP 2005 is the calculation tool for the TER and DER for all dwellings up to 450m² in floor area. The TER approximates to a 20% improvement on emission levels from a building complying with the 2002 edition of Part L and includes a 'fuel factor' that compensates for fuels that produce greater emissions than natural gas.
When to submit a SAP assessment?
a) On submission
Your designer should submit a preliminary SAP calculation to us to accompany your application - whether submitting Full plans or Building Notice applications - this will demonstrate that your design can comply with Regulation L1.
b) On Completion
On completion of the building, the developer must submit a second calculation that reflects any changes from the original design and is also based on the result of the air tightness (pressure) test carried out on the dwelling.
Both calculations must show that the DER does not exceed the TER.
Who produces the SAP assessment?
The calculations can be done by authorised (certified) SAP assessors. Uncertified ratings submitted with an application must include a comprehensive list of the input data to show that it correlates with the plans and the completed building.
In carrying out this calculation, the assessor must include an assumed air tightness rating that may have to be validated by testing of the completed building (Pressure Testing).
How are the ratings produced?
All ratings must be calculated using one of the programs that have been tested by the Building Research Establishment and approved by the Department of Communities and Local Government (DCLG) . A list of approved software can be obtained at BRE . In making a calculation, the following issues are considered: -
- Hot water and space heating systems,
- Dwelling dimensions and layout,
- Ventilation sources and airtightness standard (see below),
- U-values of walls, floors, roofs, doors and windows, and
- Solar gains.
SAP is also useful in producing a list of the features that are critical to achieving compliance. This may include a particularly low U-value to an element or a high performance heating boiler.
Air permeability (air leakage)
Until the building is complete and has been pressure tested, the air permeability figure has to be assumed for the purposes of the SAP calculation. This would usually be not more than 10m3/hour/m² at an air pressure of 50 pascals (Pa). The designer has the option to assume a lower figure than this, however a higher level of performance will need to be later confirmed by subsequent test results.
Incorrect assumptions at design stage may result in the building failing the test and ultimately may not comply.
'U' value limits
Whilst L1A gives a high degree of design flexibility - Table 2 of the Approved Document lays down 'bottom line' limiting U-Value standards in terms of individual elements together with 'area weighted' averages for walls, floors etc. These limits aim to ensure that the design is 'robust' enough not to have its performance seriously affected by future alterations such as a change to a less efficient heating system.
The inclusion of low and zero carbon systems such as wood pellet boilers, solar panels, photovoltaics and wind generators are encouraged as a positive measure to trade off against other factors in the design.
Concept Design Stage
Dsigners are advised to calculate the CO² emissions rate with the SAP calculation tool as early as possible in the design phase to ensure that the dwelling will be compliant with Regulation L.1. Incorrect design could also affect design in relation to Planning Permission.
Pressure testing of dwellings
Pressure tests need to be carried out by an independent qualified (or accredited) person following the approved procedure described in the ATTMA publication 'Measuring Air Permeability of Building Envelopes'.
In a development of multiple dwelling units, the number that needs to be tested will depend on the number of 'Dwelling Types' in the scheme.
Dwelling types are units of similar generic form and can be grouped as follows; -
- Detached,
- Semi-detached and end terrace,
- Mid terrace, and
- Apartments.
If units are built with different construction methods then these must be treated as separate dwelling types.
How many to test?
- Generally the developer will need to test at least two units of each type in a development and we will select these together with the builder.
- For less than 4 units, only one test of each type is needed.
- For sites of greater than 40 units at least 5% of each type must be tested but this is reduced to 2% where the first five units tested are found to meet the design air permeability.
- On small developments of up to two units, it is not necessary to test where the same builder has already constructed and tested a building of the same dwelling type within the previous 12 months. In these cases the earlier test result will be taken as being indicative of the performance of the new building.
There is also an option to assume a greater air leakage rate in the SAP calculation (15m3/h/m²) to avoid the need to pressure test (on small developments) but this would necessitate particularly high standards in the design in order to meet the TER.
In the future there may be a system of robust details for Part L (similar to the concept of the Part E Sound Insulation robust details) that will allow only one of each type to be tested.
Failed Pressure Tests
A pressure test that shows that the measured air leakage exceeds that assumed in the SAP calculation does not necessarily mean that the dwelling does not comply. A re-calculation using the actual test leakage may show that the DER is still less than the TER, so is acceptable. If this is not the case then it is necessary for the builder to carry out remedial measures and these would normally involve tracing sources of air leakage with a smoke wand so that additional sealing measures can be carried out followed by a retest.
Certification and the Commissioning of Heating and Hot Water Systems.
Regulation 20C requires that all such systems are effectively commissioned so that at completion, the systems and their controls are left in the intended working order It also requires that a builder provide us with certificates as evidence of this on completion of the building.
Issue of Completion Certificates
We will not be able to issue certificates of completion under the Building Regulations until we have received: -
- The final SAP calculation,
- A pressure test report (where applicable), and
- Any relevant certificates for the commissioning of controlled services in the building.
NB: In addition a notice displaying the energy rating from the SAP calculation must be prominently displayed in the new dwelling.
Operating and maintenance instructions
Regulation L.1. also requires that the builder provides new owners with an information pack for the fixed services in the building. This is to enable them to operate such services in an energy efficient manner. This can be made up of guidance provided by the manufacturers of the various components making up the systems and should give easily understood advice on making adjustments to timing and temperature controls and the necessary maintenance schedules for efficient operation.
Construction Standards and Design Detailing
Irrespective of the quality of insulating materials used, there is a major potential for heat loss and cold bridging caused by poor standards of construction in terms of air tightness and the continuity of insulation. For this reason it is important for the designer to ensure that the various insulated elements in a building are carefully detailed at junctions. Uncontrolled air leakage can be minimised by specifications calling for appropriate levels of sealing and the TSO Robust Details guide 'Limiting Thermal Bridging and Air Leakage' suggests suitable details for achieving this with typical methods of construction.
Site supervision.
The importance of effective on-site supervision to oversee that the quality of workmanship achieves the above standards should not be underestimated. The cost of delays in completion and remedial action could far outweigh the costs incurred in this process.
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