Part L FAQs

Some of the frequently asked questions answered

New Dwellings SAP

When should I get SAP Calculations done?

You should obtain a Design SAP calculation as soon as your Building Regulations drawings and specifications are completed.  It is vital to check that the design meets or exceeds the Target Fabric Energy Efficiency (TFEE). The next step is to consider options for heating, heating controls, hot water, secondary heating, lighting, ventilation and renewables, to ensure the Target Emissions Rate (TER) is met.

As a guide, with mains gas heating, a dwelling design needs to exceed the TFEE by around 12% to 15% in order to meet the Target Emissions Rate (TER) without using renewables.

If the proposed dwelling is off the mains gas grid, it is very important to consider the options for heating type and different heating fuels carefully and at an early stage.

To help with this, we offer a consultation service for clients preparing planning applications in these and other circumstances, because L1A compliance constraints for proposals can have a significant impact on the construction costs.

Is an air test compulsory?

It is not compulsory, there is an option to forgo the air test on small developments, but there is a punitive test result of 15 m3/m2.h applied to the As-built SAP calculation.  Unless there are features in the design to offset the effect of this on both Target Fabric Energy Efficiency (TFEE) and Target Emissions Rate (TER), the resulting As-built SAP will show a Fail result.

So for most convential designs, it will be necessary to have an air test done at completion to show the result is as good or better than the target rate used in the Design SAP calculation.

For large developments, it is possible to test a sample of the dwellings, to a regime agreed with Building Control.  The average of the test results for each dwelling type is applied to all non tested dwelling of the same type, but a 2.0 m3/m2.h penalty is added to the average.

We provide detailed checklists to help builders improve air tightness during construction, please contact us for more information.

Is thermal bridging important?

Thermal bridging is very important!  As dwelling fabric standards have increased, the proportion of heat loss from junctions in the external elements has increased significantly.

Applying a consistent regime to construction of junctions in the thermal fabric is a key part of achieving the Target Fabric Energy Efficiency (TFEE) in SAP, and helps achieve lower air permeability test results.

As part of our service, we will advise you on the most effective construction details and products to minimise thermal bridging in your dwelling designs.

If you would like to receive more in depth advice about thermal bridging, including CPD, please contact us.

What are the "Model Designs" in Section 5 of Part L1A?

Model designs are shown on pages 25 and 26 of L1A, and show the reference values used in the SAP software.  However it is very rare to find a design that meets every value from the notional dwelling specification.

There are a number of reasons for this, some not that obvious until examining more closely.

For example, the reference U-value for a party wall is 0.0 W/m2K, but that is for a fully filled cavity wall with sealed edges, or a solid wall.  Neither of these construction details work that well with regards to meeting the requirements of Part E for sound insulation.

We can provide advice and tips for designing as close to the notional dwelling specification, and how to close the remaining gaps, please contact us for more information.

What if the design changes during construction?

We would encourage you to ask us to check the implications for the SAP calculation of any proposed changes considered during the construction phase as soon as the occur.  This is necessary to ensure the design will still comply with Part L, or to identify any cost effective and practical adjustments in other areas required to maintain compliance.

If the changes are minor, we wouldn’t normally make a charge for this; we consider it a worthwhile investment to avoid problems for everyone later on.

We will also respond within 48 hours, to make sure the decision making process, and indeed the project, is not delayed unduly.

What happens when the dwelling is complete?

A couple of weeks before completion, an air test needs to be booked.

Prior to that though, we need to check the details the Design SAP was based on have not changed.  So we send you a simple sign-off document together with an email request for As-built confirmation specific to the dwelling design.  When we get this back, we check the calculation and confirm the air test target.

Once the air test is successfully completed, we issue an As-built L1A Compliance Checklist, SAP Calculations and an EPC.

Converted Dwellings

Do change of use conversions need a Design SAP calculation?

No, the SAP software was developed to check compliance with L1A for new build dwellings only, and from 2008, to produce On Construction EPCs at completion.

Change of use conversions need to comply with L1B, and very often compliance will be determined solely by a series of inspection visits by a Building Control Officer (BCO).

In some circumstances, when an unusual design or practical constraints mean some thermal elements cannot be upgraded, a BCO will ask for comparative SAP calculations to allow the CO2 emissions from the conversion “as designed” and an “elementally compliant” conversion to be compared.  If the CO2 emissions of the “as designed” conversion do not exceed those of an “elementally designed” conversion, the BCO will accept this as evidence of compliance.

If this situation occurs it is best to identify it at an early stage, rather than after construction has started, when things are difficult and costly to change.

We can provide bespoke L1B compliance reports supported by comparative SAP calculations to ensure Building Control accept that the design is compliant.

Contact us for more information – it is much easier and cheaper to resolve these issues before construction begins.

Do change of use conversions need an EPC?

Yes, a change of use conversion needs a SAP EPC on completion for Building Control sign-off.

Please be aware that an RdSAP (Reduced Data SAP, for existing dwellings) must not be produced for Building Control sign-off of a newly converted dwelling.

The SAP EPC is the same as an On Construction for a new dwelling, except there is no air test required and no thermal bridging calculation done.

A default air test value is used in the SAP software for the air test, and a default value for the heat loss due to thermal bridging is also applied.

Do L1B Conversions need an air test?

No, there is no requirement for L1B conversions to have an air test carried out.  A default value is used in the SAP software when the SAP EPC is being produced.

However in some dwelling designs where the heat loss envelope is upgraded and a recognised construction details scheme has been followed, it may be realistic to carry out air tests to include better results than the default value in the SAP calculation, which will result in a higher SAP rating.

This may be beneficial where the developer is obtaining a warranty on the completed work, for example.


How is thermal bridging dealt with in L1B Conversions?

The SAP calculation does not take account of thermal bridging and a default heat loss value is used for the thermal bridging when producing a SAP EPC for a newly converted dwelling.

However it would be good practice to follow a recognised construction details scheme wherever practical, and in some dwelling designs, it may be realistic to carry out air tests to include better results than the default value, which will result in a higher SAP rating.