Compliance criteria
Once the TER has been calculated compliance is met by following five criteria.

Stage 1
Check (by calculation) that the predicted rate of carbon dioxide emissions from the dwelling (DER) is not greater than the Target Emissions Rate (TER).

Stage 2
The dwelling fabric and the fixed services should have performance values no worse than the specified design limits. See ‘Limits on Design Flexibility’.

Stage 3
The dwelling should include appropriate passive control measures to limit the effect of solar gains on indoor temperatures.

Stage 4
The performance of the dwelling, as built, is consistent with the DER. This requires a check to ensure that any changes in performance and specification of materials between design and construction do not affect the TER.A final calculation of the DER is required to confirm compliance.

Stage 5
Information concerning the energy efficient operation of the dwelling should be provided to the occupier. This will include set/s of operating and maintenance instructions produced in such a way that householders can understand. This information is expected to be included as part of the ‘Home Information Pack’.

Limits on design flexibility
For design purposes the limiting U-values shown should not be exceeded. In practice the envelope standards would need to be better than the limiting values. Typically for walls design U-values would be expected to be around 0.30 W/m²K.

Limiting the effects of solar gains in summer
Designers need to check that the dwelling is not prone to summertime overheating. High mass structures perform well in this area by being able to store heat during the daytime and releasing heat as the dwelling cools down overnight. Lighter forms of construction do not possess the potential for high thermal mass.

Other steps could include an appropriate combination of window size and orientation, solar protection through shading, ventilation etc. Reference should be made to ‘CE 129 Reducing overheating – a designer’s guide’, for more information.

Quality of construction
To ensure that the performance of the dwelling as built is consistent with the DER, a check is required to ensure that any changes in performance and specification of materials between design and construction do not affect the TER. A final calculation of the DER is required to confirm compliance. If it is found that the dwelling does not comply, then appropriate remedies will be required to be taken. A checklist is provided in Approved Document L1A to aid identification of any nonconformity.

Continuity of insulation
For the building fabric, insulation must be continuous over the whole building envelope. This is primarily a workmanship issue and supervision should be in place to ensure there are no gaps in the insulation and that appropriate building details are followed to avoid unreasonable thermal bridging at the edges of openings and other junctions.

Air permeability
Appropriate air permeability tests should be undertaken to demonstrate that the design air permeability has been achieved. Details are provided in the Approved Document of the test method and criteria for selecting a testing organisation. For dwellings designed using Accredited Construction Details a less onerous testing regime is required. Criteria are also given in the event of failing an air pressure test.

On small scale developments – no more than 2 dwellings – relaxation of air pressure testing is given if a dwelling of the same type and constructed by the same builder has been pressure tested and achieved the design air permeability.
Avoiding air tests altogether can be achieved by assuming a value of
15m³/(h.m²) when calculating the DER. However, using this approach is likely to result in unrealistic performance values of building elements being required elsewhere in the dwelling.