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Building Regulations Part L & F, overheating, Future Homes and Future Buildings Standards

The announcement

The Ministry of Housing, Communities and Local Government (MHCLG) has published its response to the 2019/20 consultation on Part L and F and the Future Homes Standard

Alongside, it has published its consultation proposals for 2021 Part L and F and for the 2025 Future Buildings Standard for all buildings.

The consultation deadline is 13th April 2021.

The Future Homes Standard and Future Buildings Standard are due to be implemented from 2025.

MHCLG’s intent is that these standards set out a pathway towards creating homes and buildings that are fit for the future, and a built environment with lower carbon emissions and homes adapted to the overheating risks caused by a warming climate.

MHCLG expect that homes built to the Future Homes Standard will have carbon dioxide emissions 75-80% lower than those built to current Building Regulations standards, which means they will be fit for the future, with low carbon heating and very high fabric standards. The Future Buildings Standard consultation builds on the Future Homes Standard by setting out energy and ventilation standards for non-domestic buildings, existing homes and to mitigate against overheating in residential buildings.

The interim 2021 Part L uplift to energy efficiency requirements will act as a stepping stone towards the full Future Homes Standard and Future Buildings Standards. For new homes, MHCLG expect it to result in a meaningful and achievable 31% carbon emissions saving compared to the current standard.

This two-stage approach (2021 uplift, and 2025 Future Homes / Building Standard) is intended to support industry to prepare and position itself to build to the full standard: ensuring that a sufficient supply of low carbon heating and an appropriately-skilled workforce is in place; and that our housing supply commitments can still be met. 

Initial CIBSE reaction - new dwellings

We have carried out an initial review of the proposals for new dwellings, i.e. Part L & F 2021 and the Future Homes Standard.

CIBSE had expressed strong concerns about the previous proposals, and we are pleased to see some positive changes in line with our 2020 recommendations, of which:

  • Retaining the right for Local Authorities to set energy and carbon standards that go beyond Building Regulations. This recognises the leadership role played by many Local Authorities and communities across the country, allows more carbon savings, earlier, ultimately supporting development in the rest of the market. 
  • Retaining a fabric efficiency standard to promote a fabric first approach.
  • Accelerating the development of the Future Homes Standard, now due for draft publication in 2023. This will give confidence to supply chains and encourage early adoption by market leaders and local authorities. 
  • Omitting the proposed technology factors which would have excessively supported district heating networks by allowing heating emissions to be 45% higher. This will provide a fairer assessment of their carbon impact against other low carbon heating options.

However, we still have concern about a number of proposals, including:

  • The draft FHS specification proposes an airtightness of 5 m3/hr/m2 at 50Pa and natural ventilation. This is quite far from "world class" levels of energy efficiency. Supply chains must develop so MVHR is well designed and installed, to deliver energy savings and good indoor air quality. This should be encouraged with a draft FHS specification showing best practice airtightness and MVHR.
  • Compliance targets are still proposed to be set by comparison with a notional dwelling. This means little in real life, prevents verification in use, and does not drive passive design. We recommend moving to simpler, more effective and trackable targets such as Energy Use Intensity and/or carbon emissions /m2/yr.
  • Apart from fabric efficiency, the metrics are kept as primary energy and carbon emissions. Both are dependent on the wider system (including varying conversion factors) and mean little to consumers. They do not facilitate tracking of progress over time, comparisons between buildings, and creating a closer link with real life performance. We recommend energy use instead of primary energy.
  • Measures are proposed to address the performance gap, and this is welcome, but these stop at Practical Completion: there is still no indication from MHCLG of measures to address actual in-use operational performance. These must be looked at, possibly through another regulatory instrument than Building Regulations, for example as part of the wider regulatory regime created in response to the Hackitt Review.

You can read our consultation response on the 2019 proposals for new dwellings. We will be testing new proposals against this, as well as latest evidence and advice, including the Climate Change Committee’s 6th Carbon Budget, released in December 2020. 

Initial CIBSE reaction - new dwellings - overheating

The consultation proposes to introduce a new requirement to mitigate the risk of overheating in new residential buildings.

The new requirement is based on research into overheating in new homes commissioned by MHCLG and undertaken by AECOM. The reports of the research can be found here: The new requirement would apply to all new residential buildings including houses, flats, care homes and student accommodation. 

There are two methods proposed to demonstrate compliance with the new requirement; a simplified method and a dynamic thermal analysis method.

The simplified method provides a set of window and ventilation specifications based on the location and type of new residential building:

  • It categorises buildings into two groups based on location; those in Greater London and those in England excluding Greater London. They are also categorised into two groups, A and B, based on the number of fabric elements exposed to outdoors and ability to cross ventilate.
  • Depending on which group the building belongs to, there are specifications provided for maximum glazing area and shading (to minimise solar gains), as well as openable glazing areas for removing excess heat.

The dynamic thermal analysis method:

  • Is based on CIBSE’s TM59 Design methodology for the assessment of overheating risk in homes.
  • Provides an alternative to the simplified method that intends to allow more flexibility in dealing with overheating risk at the design stage as it allows more combinations of design options and site characteristics to be assessed.
  • Provides more detailed specifications on the window and door opening schedules that override the TM59 method. There is also a list of acceptable shading and ventilation options that could be assessed using this method. 

In addition to these two methods, the draft Approved Document provides guidance on a number of issues, aiming to ensure the overheating risk strategy is robust. This includes guidance on: acceptable noise levels at night, pollution (based on Part F), security, protection from falling (increased levels from Part K) and entrapment, that will need to be considered when assessing the natural ventilation capacity of the domestic units.

CIBSE’s initial response on the overheating proposals:

CIBSE has always expressed concerns about the potential overheating risk in homes and the need for a treatment to be introduced in the regulatory framework, so we are welcoming the new overheating requirement, as a dedicated requirement in Building Regulations.

We also welcome:

  • the recognition of what simplified methods as well as dynamic modelling can bring to assessing and mitigating overheating risk, to deal with a range of stages and complexity of design.
  • the introduction of CIBSE TM59 as a method for compliance, within the dynamic thermal analysis method. 
  • The recognition that overheating in practice is influenced by a number of contextual factors, such as noise, and that it must be addressed with a range of considerations in mind in order to protect the health and wellbeing of occupants, including air quality, usability, and safety.

Beyond these points of principle, we have started to analyse the details and will provide more detailed comments in the near future. In particular, we are interested in feedback on the simplified method and its criteria for building categories, especially proportions of glazing.

We still have concern about the existing domestic stock and the amount of properties that are currently experiencing overheating.

Initial CIBSE reaction - new non-domestic buildings

There are a number of positive elements in the proposals for new non-domestic buildings for the Future Buildings Standard and the interim 2021 uplift, of which:

  • Clear statements about the importance of heat decarbonisation, which has a large place in the FBS consultation; this includes statements anticipating a central role for heat pumps, along with heat networks and, to a lesser extent, direct electric heating. The consultation does not anticipate a role for hydrogen in the timescale considered, which aligns with the CIBSE view.
  • Clear statements acknowledging the performance gap, and the role of modelling methods, commissioning and compliance checks contributing to it, with some measures to address it through Building Regulations and through changes to SBEM and the NCM to “better account for energy uses and incentivise appropriate design solutions”.  
  • An intent to strengthen commissioning requirements. We recommend going further and considering a penalty in the Part L as-built calculations until evidence of commissioning is provided, at least for complex systems and large buildings (e.g. x% worse efficiency).
  • Proposals to bring more attention to modelling of energy performance beyond regulatory compliance modelling, with a reference to CIBSE TM54.

However, CIBSE have concerns about a number of items, many of which we have already raised with MHCLG, including:

  • A per our comments on proposals for new dwellings, we are concerned about the continued reliance on a notional building, and the use of primary energy and carbon emissions as the two metrics: both do not facilitate comparisons of building performance itself, and do not mean much to consumers. Energy use must become a key metric in the evaluation of building performance for regulatory purposes.
  • Furthermore, we do not agree with the statement that a primary energy metric enables government to prioritise “the energy efficiency of the building fabric regardless of the heat source”; primary energy does take account of the heat source. Prioritising fabric efficiency could be achieved through a metric such as thermal demand (more on this below).
  • We have received repeated feedback that space heating is often under-estimated by NCM. While the consultation talks of improving NCM to reduce the performance gap, it does not acknowledge this particular issue nor suggest changes to the heating calculation method. This may be incorporated in the detail of the proposals, which we have not yet analysed. >> CIBSE are looking for feedback from members on this issue, please contact us if you have information which could contribute to our response e.g. regulatory vs TM54 modelling, regulatory vs in-use space heating, thoughts on improvements to the methodology.
  • The consultation states the intent is to retain “performance-based standards”. However, this is undermined by two aspects:
    • Keeping the approach of using a notional building in both the 2021 uplift and the FBS. This does not incentivise attention to building form and all passive design measures. Performance is compared to a building of the same shape, not an absolute level of performance which would be the same for all buildings of the same type.
    • In the 2021 uplift, varying the heating fuel in the notional building depending on the fuel in the actual building. In particular, gas buildings will be compared against gas buildings, which is clearly not an incentive to heat decarbonisation. All other things being equal, a gas building will have higher carbon emissions than one heated by heat pumps, but be assessed as performing the same under Part L. Similarly, buildings connected to heat networks will be compared to buildings connected to a heat network, including an additional carbon allowance instead of encouraging an evaluation of building-based and network solutions on a like-for-like basis. This provides artificial support factors for particular systems, rather than a real performance-based evaluation. Our initial reaction is that this approach would not fully grasp the “opportunity to start to establish a mass market solution for low carbon heating with new buildings”. The assessment of buildings and their heating systems must be on a like-for-like basis to allow a robust and consistent evaluation of options, and accelerate heat decarbonisation.

Next steps and further work to develop the CIBSE response

CIBSE will continue to analyse the proposals and will work with industry to develop our response. In addition to the issues above, we are very interested in contributions on the following:

  • Heat pumps: The government’s assumptions and proposals for heat pump applications per building type, the assumptions on their efficiency and applicability depending on the space heating and hot water usage profiles, and the proposed implementation timescale of the full Future Building Standard across different building types, taking account of technical aspects as well as supply chain development.
  • Fabric and thermal demand metric: Government proposals are hinting at a new metric or a new way to encourage fabric first approaches in the FBS. In dwellings, CIBSE have been advocating for a metric such as space heating demand or Heat Transfer Coefficient. In non-domestic buildings, space cooling would also need to be considered. We are interested in views and evidence on the best approach e.g. a combined space heating & cooling metric, or separate heating and cooling ones, or another approach altogether.
  • Government states their preferred option for the Part L 2021 uplift is a 27% carbon reduction compared to Part L 2013. We need to do more analysis of the proposed fabric and services parameters. In addition, we have not yet been able to determine whether this is on a like-for-like basis or whether it includes the benefits of grid decarbonisation, in which case this would not be a sufficient step.

Get involved

Following on from our work on the 2019/20 consultation, we will produce responses to these hugely important consultations. We are very keen to work on this with our members, industry, and other organisations, so please get in touch at if you would like to be involved and support our work.

Deadline for email contributions to us is 13th March 2021 but we have started working on our draft response with interested people so do get in touch earlier if you would like to be involved.

Stay informed

We are going through the proposals on Part F and on existing dwellings and existing non-domestic buildings, and will provide an initial analysis of these shortly.

We will provide further updates on ways to be involved with the CIBSE response and on our analysis of the proposals. Please check this page and the consultation page regularly. 

For information on CIBSE's ongoing revision of Testing buildings for air leakage (TM23), click here: TM23 Revision