Net zero design: the Future Homes and Buildings Standard

Government net zero proposals for the Future Homes and Buildings Standards gave CIBSE Members plenty to digest over the Christmas period. Alex Smith looks at the proposed changes and how they will affect the specifying of low carbon technologies

The publication of the Future Homes and Buildings Standards (FHBS) consultation last month was intended to put the UK firmly on the path to net zero carbon. 

Due to come into force in 2025, the standard sets performance requirements to ensure new homes and non-domestic buildings are ‘zero carbon ready’ so that no further work is required when the electricity Grid is decarbonised. This rules out fossil fuel heating, including hybrid and hydrogen-ready boilers. 

One thing the standard will not do is change the minimum building fabric standards. The government has said that the 2021 uplift in standards in Approved Document Part L, which have applied since June 2022, were intended to meet the specifications in the FHBS. 

However, improvements are proposed to the minimum standards for fixed building services and onsite electricity generation. There are also plans to improve guidance and minimum standards for heat losses from building services that directly support the installation of ‘zero carbon ready’ technologies.

The government expects low carbon heat networks to be a key route to compliance. New buildings can be connected to existing heat networks, but they must meet the performance requirements laid out in the FHBS. This means they must use heat supplied by low carbon networks or low carbon extensions to existing networks that may be powered by gas boilers.

New performance requirements

New ‘notional buildings’ are proposed to set the standard for homes, non-domestic buildings and heat networks. Notional buildings are benchmark specifications that meet performance standards, and they can be used by engineers and architects to model the performance of their designs, to gauge whether they meet the requirements.

Two domestic notional building options are proposed. Option 1 maximises carbon savings and reduces energy bills, but has higher upfront costs for the developer because it features more low carbon technologies, including PV panels, decentralised mechanical extract ventilation, and wastewater recovery. Airtightness is also higher than Option 2, at 4 rather than 5m3 .h-1.m-2 @ 50Pa.

For blocks of flats of more than 15 storeys, solar panels will be removed. For single-storey dwellings, wastewater heat recovery systems will be removed, as horizontal systems are more expensive and less efficient than vertical ones. 

The heat network notional building has similar options to above, but a 4th-generation heat network is assumed, with primary losses of 12% and a seasonal coefficient of performance (SCOP) for plant of 3.0.

For non-domestic buildings, the proposals base notional buildings on two sets of proposals: one for top-lit spaces in buildings and one for side-lit spaces. A heat pump is proposed for side-lit spaces and radiant electric heating in top-lit spaces. Enhanced efficacy of lighting and heat-recovery efficiency is also proposed.

Like the proposal for homes, there are two options for non-domestic buildings, one with roughly double the amount of PVs for both side-lit and top-lit spaces. The government recommends option one, with higher levels of PVs. The consultation proposes the same fabric requirements as the 2021 standards, with the exception of warehouses and sports halls, which would have higher levels of airtightness to support the installation of low carbon heating.

Updated guidance and minimum standards

There are plans for higher minimal standards for building services, including: heat pump efficiencies and controls; comfort cooling efficiencies; ventilation system efficiencies; lighting efficiencies; and fixed lighting controls. Standards will also apply to existing homes.

In response to smarter, more complex heat pumps, the government also proposes additional guidance on heat pump controls and wants to see more information fixed to the heat pump or hot water vessel.

There are also changes to guidance to limit heat loss in new homes, with new minimum standards for hot water storage vessel insulation; the consultation says increasing insulation standards is necessary to ensure good heat pump performance. 

There are proposals to change minimum building services efficiencies and controls for new non-domestic buildings. Heat pumps will follow Ecodesign Regulations and heat pumps not covered by these should have a minimum COP of 2.5. Minimal standards for lighting and heat pump efficiencies will also apply to existing buildings. 

To limit heat losses from building services in new communal areas of flats and non-domestic buildings, the government is proposing to refer to CIBSE CP1 Heat Networks: Code of Practice. This provides insulation standards for building heat distribution systems that contain multiple dwellings. It will also refer to CP1 for heat distribution system installations in new apartment blocks.

Lifts, escalators and moving walkways are not covered by the notional building and National Calculation Methodology, so new minimum standards – using calculations and testing/commissioning standards made under the BS EN ISO 25745 standard – are proposed. 

New standards for material change of use

The consultation is proposing to improve the performance of buildings that have been converted from one purpose to another (material change of use) by setting better fabric and building standards. 

The consultation is also looking at widening the scope of Part O of the Building Regulations to include homes created though a material change of use (MCU). Currently, Part O only applies to new dwellings or other residences. The consultation says that extending Part O to MCU has potential for climate adaptation benefits. 

It says the Building Safety Regulator is carrying out technical research on the impact of applying the Part O requirements to homes created through a MCU, with the research planned to be published in 2024.

Ensuring real-world performance

The proposals are looking at two ways of improving the real-life performance of homes: fabric performance testing and better Home User Guides. 

Different options are being explored for a performance test for developers. The government wants it to be simple, scalable and non-intrusive for occupants, and says that a smart meter-enabled thermal efficiency rating (SMETER) could be the most suitable method. This will require smart meters to be more widely installed, so the government plans to update guidance for their installation and commissioning in four key areas: the location of installations; spacing around smart electricity meters; materials that block signals to the communications hub used by the smart meter; and logistics.  

There are ongoing concerns about poor designs and installations of ducted ventilation systems leading to
fans operating at near maximum to achieve design
airflow rates. This leads to excessive noise, high fan running costs, and a shorter fan life. So, when installing centralised mechanical extract ventilation or centralised mechanical ventilation with heat recovery, the consultation proposes that static pressure and total
power consumption be measured.

The success of the Future Homes Standard will depend on heat pumps and mechanical ventilation being installed well, says the consultation. There are two routes to certification of these works: installers can self-certify or a building control body can do so. Guidance on this will be added to Approved Documents, as will details of enforcement action if work is not to standard.

For domestic buildings, the government is separately consulting on the new Home Energy Model, which will replace the Standard Assessment Procedure for the energy rating of new homes. 

To help readers evaluate the proposals, the Department for Energy Security and Net Zero has published a Home Energy Model: Future Homes Standard assessment tool. On the National Calculation Methodology (NCM) website there is a consultation version of the NCM and the Simplified Building Energy Model that implements the methodology. 

Developers won’t have too long to get to grips with the changes. The FHBS will come into force either six or 12 months after the legislation is passed in 2024, and there will then be a 12-month transitional period. 

  • Details of how to respond to CIBSE’s submission to the consultation will be available at