Round table review: ‘Solutions for Compliance: Part L and beyond’


On 24 May 2023, at London’s Building Centre, netMAGmedia staged its first construction round table to bring housebuilders, architects and suppliers together to discuss the current challenges posed by Part L, but also look forward to the Future Homes Standard. The event was sponsored by glazing, bifold and sliding doors manufacturer IDSystems, thermal breaks manufacturer Schock, and PIR insulation manufacturer Recticel. Here James Parker, editor of Housebuilder & Developer and event chair, reports on the highlights.

We staged our first industry round table a month before the legal requirement was brought in for all new homes to comply with the new Part L of the Building Regulations, which requires them to produce 31% fewer carbon emissions than the previous Regs. This is a key step towards the 2025 Future Homes Standard, which will require a much more demanding 75%-80% cut in emissions, meaning major changes to both building fabric, design, and integration of renewables and alternatives to fossil fuels.

Our well-timed event saw representatives from housebuilding and architecture sharing their current issues with Part L, as well as our suppliers contributing valuable insights on the benefits as well as difficulties being experienced in complying with the requirements. There were candid revelations on attendees’ perception of the Future Homes Standard, such as on the current timeline in the context of the industry’s remaining challenges. 

As well as Part L, the updated Part F on ventilation and the new Part O on overheating came under scrutiny, and the required trade-offs in order to achieve one standard without failing on the other, with the tighter U-values tending to mean challenges on avoiding excessive overheating. The event also saw discussions around challenges in terms of future homes’ aesthetics, and how the planning system remains a stumbling block.

Building Insights LIVE was an unusual opportunity to host a frank conversation around compliance with the new regs, specifiers and key suppliers exploring how to harness different aspects of building fabric, in particular. It also used the reader survey data collected in our Industry Viewfinder white papers as a springboard for elements of the discussion. 

Following this successful first event, we will be holding more Building Insights LIVE round tables in future, beginning with a round table dedicated to Solutions for Stormwater Management in October.


The first question on the agenda that the panel discussed was whether cutting 31% of emissions as a result of Part L 2021 had been a major headache, in the context of current pressures such as skills, materials supply chain issues, and inflation.

SME housebuilder Chris Carr said that his firm was struggling with the fact that they were “trying to build with materials that were not fit for purpose in some cases.” He explained further, saying that “materials quality and design have not improved with the policy,” i.e. the new central drive to produce much more energy-efficient homes than the industry has been accustomed to.   

This issue of a lack of rigour when it comes to skill levels among subcontractors feeds directly into the performance gap between design and build. “Unless we engage them, we are going to have a problem,” he said. 

Architect Chris Perry said that with his practice principally working on London residential schemes, they were already designing to a performance level well beyond Part L, as the London Plan requires all new homes to be ‘net zero.’ He suggested that for this level “around 60%” of compliance was possible using fabric improvements, and “topping the rest up with PVs.” Based on this, said Perry, the 31% cut in emissions in Part L could be “easily achieved, at least in theoretical design terms.”  

Perry added that “it’s when you get to site that you hit problems,” adding that most of the headaches he had experienced “had come from suppliers,” as well as achieving Part O when working with a more energy efficient fabric, and embodied carbon.” The latter is not covered in Part L, but reducing it is fundamental to achieving the UK’s legally binding 2050 net zero goals.

Tzeh Bin Cheong from Shepheard Epstein Hunter described issues experienced on a couple of the architecture practice’s ongoing London residential projects, where wall thicknesses and other fabric measures had been upped significantly to comply with the London Plan (35% lower emissions than Part L). He agreed with Perry that problems had arisen making the trade-offs between Part L’s stipulations on U-values and the resultant impact on overheating and Part O compliance. He gave the example of a new build residential scheme in Redbridge inherited from another practice, which was now being redesigned with smaller windows in order to balance compliance with both Parts L and O. 


We asked our attendees to submit comments or questions for discussion during the round table. Simon Blackham from PIR insulation firm Recticel’s offering was that fabric-first “should be the default starting point; a back-to-basics approach that gives a robust, reliable platform for renewables.” However, would improvements to the building fabric alone be a realistic solution for the Part L 2021 requirements, or was including renewables a given?

A 2022 BCIS survey of housebuilders found that nearly 45% were using air source heat pumps within their solution to meet Part L, set against 30% favouring gas boilers and PV, and the remainder selecting a hybrid approach. The heat pumps industry accepts that the required efficiencies will only be realised with a low U-value fabric, a view echoed by attendees.

The key fabric elements of windows, insulation, and thermal breaks were represented by our sponsors. David Clarke from IDSystems admitted that across the glazing industry generally, “products are designed to meet the regulations, not to go far in excess,” which could raise issues around Future Homes Standard compliance. He added that the “historic” tendency of choosing the most cost-effective product “is now having to change.” 

Chris Carr said that getting installation right was the key, and during his time as joint chair of the Zero Carbon Hub’s ‘Design vs As Built’ project, the Hub identified that thermal bridging was “the one thing that was failing dramatically” in terms of as-built performance. 

Architect Chris Perry concurred, saying that “it is the most frustrating thing when you go to site and can see gaps between insulation sections,” adding “it makes it all a bit pointless.” Chris Carr said that his housebuilding firm was now getting joiners to install PIR insulation, as bricklayers “just want to lay bricks and blocks.”

Blackham echoed David Clarke of IDSystems, saying that delays to getting products tested was hampering results across the sector on energy efficiency. As well as dealing with a limited number of testing sites, he said “we’ve got the June 2025 deadline of CE marking no longer being recognised,” though the new UKCA mark “was exactly the same as a CE mark.” David Clarke agreed that the lack of testing facilities was also causing major challenges for firms looking to supply ‘net zero ready’ homes for the Future Homes Standard (currently slated for 2025).

When it comes to the biggest compliance issue for housebuilders, Carr says it’s providing the ‘BREL’ photo BREL evidence of proper installation across every area of a site. For example, “you need to get ducting spot on, but on a building site, it’s whoever’s there first that takes priority.”  


Chris Carr said as a housebuilder he took a slightly different approach to the ‘fabric first’ mantra, in the interest of delivering what customers want: “We’ve gone design first, fabric second,” he told the panel. “We’re looking at building houses ‘from the inside out’ – we need to know what we can do inside, including in terms of floor space, before we look at the facade.” He mentioned an ongoing development which had outline planning for 240 homes but his firm is looking to build 137 instead, in order to offer the space that customers want. 

Shikha Bhardwaj from Hawkins\Brown said that one of the remaining issues was that the housing sector is talking about U-values, net zero and PVs, “but is not actually talking about the comfort of the occupants, which is absolutely essential.” She said that just focusing on heat pumps was counterproductive to creating a product that consumers will buy into: “They are part of the strategy, not the strategy, and step one is to better understand what the occupants want.”

Chris Carr remarked that in terms of improving ventilation and natural ventilation in line with the new Part F, there had been research work underway (with Arup) looking at cross-ventilation of apartments, immediately pre-Grenfell. However, following that event, getting cross-ventilated designs on the table was “suddenly not the best idea,” but he added that “whichever solution we find, has to be adaptable for everybody.” 


In our 2022 Industry Viewfinder audience survey conducted on Part L, 65% of respondents thought that added cost was the biggest challenge, and the estimated average £10,000 extra per unit would be passed on to customers by 77% of respondents. However at our round table, Chris Carr said that the cost increase would actually be 10% per house for his firm (around £30K-£40K), a huge increase on some estimates which have put it as low as 3.6%.

The quality of installation is clearly at the core of ensuring that fabric measures have the desired result, particularly in terms of customer confidence, which was damaged again following botched Green Deal installations. Simon Blackham said that in order to make things easier for installers, Recticel introduced a tongue-and-groove full-fill PIR board solution which has become a major part of its domestic business. It is designed to be simply installed in narrower cavities than would normally be required to achieve that U-value level.

Chris Perry said that his own research had found that creating ‘net zero’-ready homes for 2025 would be around 15-20%. He added that consumers “are willing to pay 10% more for a zero carbon home,” but that “the value it adds is really more than that.” He added: “Imagine we were in a tech industry, there’d be so much development into reducing the costs, because it’s something people want and are willing to pay for.” Chris Carr however said that more of his customers needed to be persuaded of the reasoning for the large cost uplift.


Shikha Bhardwaj said that in order to avoid overheating and comply with Part L, the industry “needed to have a conversation about internal heights, as we end up doing designs for 2.5 metres and these heat up quickly.” She added that it’s “a balance between comfort, carbon, energy and what the developer wants.”

The Standard Assessment Procedure (SAP) and its associated challenges came up several times during the discussion. Chris Perry said that an unfortunate side-effect of the need to make SAP very flexible to balance policy across various building typologies was that it has ended up “so opaque.” Bhardwaj said she worked closely with energy consultants on projects to “identify whether the energy figure they were aiming at is sensible.” She explained further that “In SAP, you can only benefit from a certain U-value up to a certain point.”

Chris Carr said that with temperatures rising in coming years, UK developers should be looking to countries  such as Spain for inspiration, such as by including shutters. “We are looking at a design of shutters sliding across which will block the sun completely in summer, but which in summer are also a thermal break.” He added: “We are trying to reinvent the wheel. Maybe we just need to look what other people are doing.” Bill Hayward of Schock countered: “No-one wants to pay for it, that’s always the issue,” but Carr responded that with Future Homes Standard homes costing “20,000 plus per unit” more, “some of these other products become commercially viable.” 

David Clarke of IDSystems submitted a question: ‘Where does the balance lie between glazing performance and appearance that is going to be necessary for Part L compliance?’ He said his customers “have got used to seeing inside-out living, and floor to ceiling windows,” but added “we know that is not necessarily going to be achievable.” Bin from Shepheard Epstein Hunter responded with a challenge to the floor-to-ceiling window specifiers: “Our energy consultants keep telling us that anything below the waist in terms of glazing is a waste.” 

Chris Perry asserted that the only way to hit the balance between Part L and Part O, especially with the Future Homes Standard, is “modelling and testing.” He said an MEP engineer has to be involved “right from the start,” and that “the very big housebuilders are already doing this, but at the smaller scale it hasn’t got through.” Chris Carr said that modelling had to take into account the “as lived in” performance of homes, as “a priority, and work backwards from there.”


Chris Carr suggested that as there were issues around planners’ engagement with building performance currently, Building Control should be brought into pre-application meetings to help them achieve the right between the standards. He told the group: “Planners aren’t interested in how it physically works – you have to educate them on why we are doing certain things that affect the look, such as why we can’t put PVs on the rear of all the properties.”

Shikha Bhardwaj said planners “needed to change their mindset on how ‘ugly’ a zero carbon home will be.” Bill Hayward of Schock added that there was a ‘not invented here’ syndrome of conservatism present in planning departments which needed to change: “They need to be prepared to let go of what they know, if it’s a new technology, you have to do so much work to get any agreement.” 


The second session of the discussion moved onto a glimpse of the not-too-distant future – the jump in performance that will be required in 2025 to produce ‘net zero ready’ homes, and meet the Future Homes Standard (FHS).

David Clarke of IDSystems candidly admitted that in the event that triple glazing was required, some of the firm’s current window systems would be “obsolete.” Chris Perry pointed out a further issue around triple glazing however, in that it significantly adds to a project’s embodied carbon.

Clarke added that with budgets normally under pressure in one-off house projects, it was difficult to persuade homeowners to specify windows that were ‘future-proofed’ against the incoming FHS, rather than ones which just meet current Regs: “It’s very difficult when it’s something they’re not necessarily going to immediately see the benefit of.”

However, one area where the FHS would lead to real beneficial change in specification, according to Bill Hayward, was that products would be treated “as part of a system rather than individually. At the moment, you solve one problem, and create another one,” he said. David Clarke concurred, adding: “It’s counterproductive to just aim for that U-value figure, because you may not be taking into account that if you went slightly better, you impact the whole fabric.”

The BSI has found that thermal bridging can cause up to 30% of heat losses, but there were design challenges in resolving them, said our panel. For example, Chris Perry cautioned that “massive cavities” can result in needing bespoke ties and other structures, thereby increasing a project’s embodied carbon for one.   

However for suppliers there are obvious benefits to the jump in performance required: David Clarke said that what were currently potentially “overly efficient products” which have been on the shelf are now seeing the light of day in specifications.

Chris Carr said he was concerned that the in-demand bungalow designs his firm produces are unlikely to be achievable under the FHS, but advocated brick slips in order to produce bigger cavities without losing floor area, as brick is “decorative, and not load bearing.” He continued however that achieving this was compromised by issues like brick firms saying lintels were “not ready for it,” but asserted “there was no reason we can’t do it now.”

 He added that the standard balcony designs he uses for homes were “having to be redesigned, because there’s no way we can get them through the new Regs, and definitely not through the Future Homes Standards,” and dormer windows will be unlikely to be a feature post-2025. They have been advised that balconies will need to be “completely separate” from the structure to avoid thermal bridging. He’s lobbying the Department of Housing to push back the FHS deadline by at least two years, due to concerns from SMEs around obtaining materials in competition with volume housebuilders.

Air source heat pumps are likely to be the de facto space heating solution for the FHS in 2025, as gas is phased out. Chris Carr said that his firm was looking at PV and battery storage, plus electric heating on the ground floor of properties, and “potentially infrared heating on the first, because I’m really worried about people being cold in these houses, and infrared can provide a boost.” However he did add that “if you get the fabric and design right, it’s not going to take a lot of heating,” and his firm was going to 150 mm cavity insulation currently. 


Simon Blackham reckoned that the main issue for delivering the Future Homes Standard was “skills,” but also identifying what ‘net zero ready’ actually means. He also expressed concern that the progress to the standard was currently “piecemeal,” and beleaguered by the five year political cycle. 

Blackham exclaimed that ‘zero bills’ houses are “surely where we should be going,” given the extent and danger posed by climate change globally. The round table showed there was still a long way to travel on this road before the industry is ready to deliver this. 

Bill Hayward, echoing Chis Carr’s remarks, suggested that “maybe the answer is to reduce what we are trying to achieve; maybe we need to break it down into smaller parts.” One final moment of consensus around the table was that thanks to the Government not having “made its mind up” on the way forward, our panel believed the Future Homes Standard will not be implemented in 2025, although it is technically achievable. 

Chris Carr revisited the Government’s ‘build beautiful’ idea finally, but said that to meet the new regulations, it would be a case of “build practical, and try to make it as beautiful as possible.”

We would like to thank our round table sponsors IDSystems, Schock and Recticel for supporting Building Insights LIVE


Our attendees provided recommendations to both help the industry towards Part L compliance, and to tackle the upcoming Future Homes Standard.

Chris Carr: Planners need to work together with Building Control officers, and we need exemplars to share good practice of design and delivery. We also need to delay the Future Homes Standard by two years minimum, due to materials issues.

Shikha Bhardwaj: It’s looking at net zero carbon as a bigger challenge than just focusing on compliance, and instead using compliance as a layer of it, not the entire solution. Also, we need to focus on user comfort.

Chris Perry: The early stages of the designs are now even more important, and you need to have everyone on board to create something that works in a holistic way, and so you don’t hit problems later.

Simon Blackham: There’s a need for clarity; it’s not beholden on manufacturers to approve something which we haven’t designed to be used in a certain way.