The Fabric Energy Efficiency Standard for a Zero Carbon Future ( FEES )

Building Regulations Part F in Northern Ireland were updated in October 2012, delivering a 25% improvement over the previous regulations, with regular reviews planned over the next number of years to deliver the Government's commitment to Zero Carbon. Those designers and builders who have been providing social housing have been building to at least Level 3 of the Code for Sustainable Homes (CSH) some even further to Levels 4 & 5.

So many of our builders and design teams are now well conversed with the requirements of the new 2012 Part F because the regulations have caught up with the Code Level 3 and in terms of the energy requirement alone the current building regulations in Northern Ireland will provide a Code 3 equivalent house. This is welcome news for the buyer of private new build also were the running costs for ‘regulated’ energy uses ( heating, hot water and lighting ) should be decreased by 25% from what they were previously.

The road to Zero Carbon

In July 2010 the UK Government confirmed its commitment to ensure that from 2016 new homes in England and Wales are zero carbon and it published a new version of the Code for Sustainable Homes that gave significant signposts as to what the Zero Carbon Specifications would be.

This research has been facilitated by a task group from the Zero Carbon Hub who have worked closely with experts within the industry to look at a more workable and cost effective way of achieving zero carbon compliance. Over the last few years it has been recognised that a focus on carbon reduction without regard to the efficiency of the building fabric is not a practical or cost effective way of reducing carbon and energy use. In theory any dwelling could be made zero carbon if enough renewable energy sources were employed to offset the carbon use but this would be prohibitively expensive and not sustainable in terms of the ongoing costs and manufacture of the renewable technologies. A ‘fabric first’ approach has been recognised with the requirement to set minimum standards for fabric heat loss.

As part of that strategy a Fabric Energy Efficiency Standard was developed that set the performance levels for the building fabric that would reduce the amount of energy required to heat a home and reach the Zero Carbon standard.

The FEES sets a maximum limit on the amount of energy (in kWh/m2/year) that would normally be needed to maintain comfortable internal temperatures in a home.

For a home to be 'FEES compliant', the fabric must be sufficiently efficient to ensure that heating energy demand does not exceed these figures

The Part L Building Regulations 2013 consultation refers to two possible levels at which to set the minimum fabric energy efficiency, referred to in the regulations as the Target Fabric Energy Efficiency, or TFEE: In this case,  a target FEE  would be set at:

39 kWh/m²/yr for apartment blocks and mid-terrace houses

46 kWh/m²/yr for end-terrace, semi-detached and detached houses

Full FEES is the standard which a task group led by the Zero Carbon Hub recommended as the minimum requirement for zero carbon homes.

There are a number of key areas that need to be addressed when improving fabric performance:

  •  Building fabric U-values
  • Thermal bridging
  • Air permeability
  • Thermal mass
  • Features which affect lighting and solar gains

The new emphasis on Thermal bridging and Y values

Like every other component in a specification such as the boiler efficiency, the area of windows, the U-value of the wall, the way in which the insulation is installed at junctions and how that junction copes with heat loss has a numerical score - the 'Y' Value.

Until Part F was revised in 2010, the Y-value was defaulted at a figure of 0.15, but a target of 0.08 was deemed to be more appropriate to meet the regulation standards. This was assumed to be a figure of 0.08 by using the Acceptable Details for Construction (ACDs) published by the Department for Communities and Local Government.  A SAP assessor was permitted to use the assumed 0.08 figure within his calculations, if the details were signed off on site.

A further improvement to 0.04 could be used if the Enhanced Details for Construction published by the Energy Saving Trust were adopted on site. However from 2010, and assumption on the Y-value can no longer be made - it MUST be calculated for each project, with PSI values for each junction being taken from Table K of SAP or by using calculated PSI values from an accredited source.


The attainment of FEES is now a standard measurement in SAP 2009, it is one of the first results that is calculated on your results page next to the TER & DER for the design, so those energy assessors working on you SAP can tell you immediately what you are achieving on the FEES scale.

Carbon Zero task group terms of Reference
Carbon Zero task group terms of Reference

FEES Targets for Zero Carbon construction for reference

(Conducted in a range of dwelling types)

U-value                                Unit (W/m2K)

Walls                                     0.15 - 0.18 W/m2K

Floors                                  0.13 - 0.15 W/m2K

Roofs                                    0.13 W/m2K

Glazing                                 1.2 - 1.4 W/m2K

Doors                                    1.0 - 1.4 W /m2K

Thermal Bridging            0.04 - 0.07 W/m2K (V-Value)

Air Permeability             5.0 - 5.2 m3/hr/m2@50Pa