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Enhabit Blog » Musings on the Part L and F Response to the Consultation Document

Musings on the Part L and F Response to the Consultation Document

The Government has finally released its response to the Part L and F consultation documents that it launched, back in those pre-Covid days when we were all focussed on the Climate Emergency. The documents try to give direction of travel from now to 2025 when the Future Homes Standard will be introduced and the interim steps on that journey.

This blog is not a comprehensive romp through the documents released last week, but rather an opportunity to highlight items that seem pertinent to England finally asking its construction industry to produce energy efficient homes; we’ve been waiting a long time. It is worth noting that the Climate Change Act came in 2008 and we were promised Zero Carbon Homes for 2016. One can only assume that the fact it has taken so long, in so many fits and starts must be down to the lobbying of the volume housebuilders at the time.

So, what are the headline grabbers?

Low response rate from builders

Well, let’s start with something that most will not pick up on, but I believe is quite interesting. The response document highlighted that an unusually large number of people took time to respond to the consultation but only 134 builders decided to respond. Are there only 134 builders left in England? Do these 134 represent the industry? Conversely, 1449 designers and engineers did sit down and wade through a very big document, all credit to them and the campaigners from LETI and ACAN networks who encouraged them. Further, it seems this cohort was pretty damning in condemnation of the consultation document as not ambitious enough. A mere 28% of respondents said the Future Homes Standard was too ambitious and for some thought that the increased levels of thermal comfort would lead to increased energy bills. Work that one out……

Zero carbon energy

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Early on in the response document, we are told that the ambition is that all homes will be ‘zero carbon ready’ becoming zero carbon homes over time as the electricity grid decarbonises without the need for further costly retrofitting works. This will be detailed in the “Clean Growth: Transforming Heating” plan to be published one day soon, probably 2024, seeing the speed so far displayed in this process. Clearly, they feel that the only currently viable technology for providing zero carbon energy to the home is via the electricity Grid (e.g., heat pumps).

Effectively, the Government has signalled that they do not expect to see mains gas boilers installed in new homes after 2025. Perhaps the surprise is that it has remained at 2025 and not brought forward to 2023 as some pundits and politicians suggested during 2020. One suspects that the reality of training sufficient electricians and plumbers to install heat pumps over a two-year period and gear up the supply chain put paid to that idea.

Interestingly, hydrogen appears to have been side-lined as a home heating energy source, despite widespread support from the fossil fuel industry as the next wonder fuel, and mentioned by Boris in his 10-point plan. Hydrogen in cars has already been debunked and it remains to be seen whether it can be stuffed down the gas Grid without leaking and causing embrittlement on the way. Green hydrogen from electrolysis is the holy grail, but it is an inordinately expensive and energy-hungry process. 1kWh at the wind turbine to the heat pump in the home will produce about 2.4kWh of useful heat. Conversely, 1kWh at the wind turbine may produce only 0.3kWh heat from a domestic hydrogen boiler. Let’s hope that our politicians can ‘do the math’.

Heat networks got a mention and the Government wants to encourage their uptake, but clearly, they were torn between the efficiencies of a large central plant and the high distribution losses coupled with the fact that most current heat networks are mains gas-fired and that is not zero carbon. The UK has never adopted heat networks at anywhere near the levels seen across the Continent and it remains to be seen if we ever will. Higher levels of home ownership may preclude this being a feature in the UK, coupled with the high installation cost that most developers would have baulked at over the decades.

Government climb downs

Autonomy for local councils

The first climb down we see is that for the period up to 2025 Councils can retain powers to set local energy efficiency standards via the Planning and Energy Act. There is guidance that Code 4 should be the limit in terms of energy uplift which is a mere 19% better than Part L1A 2013. It would set a fantastic precedent if forward-thinking Councils will try to push that envelope and make Passivhaus the minimum standard for all developments between now and 2025.  Would any Government tell a Council in 2025 that they must allow new homes to be built to worse standards, where the council had already adopted Passivhaus for some time?

Fabric Energy Efficiency Standard (FEES)

The second climb down was that they decided, after a huge wave of negative press, that the Fabric Energy Efficiency Standard (FEES) would be retained after all. Many of us, quite rightly, argued that if a Fabric First approach was what you wanted, it seemed strange to kill off the only metric that measured it!

Transitional arrangements

The Government confirmed that transitional arrangements would be changing. Previously, in the run-up to Part L changing, we would see local authorities explicitly encouraging developers to submit a Building Regulations application in the days and weeks before the latest version of Part L1A coming into force. This would then allow developers to keep knocking out leaky mock-Georgian rabbit hutches for many years to come. We are aware of estates still being built to 2006 regulations. Now transitional arrangements will be on a house-by-house basis. The developer will get a year’s grace for each house to make a start under the old regulations. However, there are significant ‘get out of jail’ clauses, which, no doubt, will be exploited to the full. Commencement on a house build can be as little as pulling the footings, putting in drainage to the unit or scraping away the topsoil for a raft foundation. Expect to see housing sites resemble the battlefields of WWI with “shell-holes” excavated in a long line, like a string of inverted molehills across a lawn. The fun starts in June 2022 and the new arrangements take hold in June 2023. Therefore, developers have until June 2022 to get their Building Regulation Applications in and make a start by June 2023, another two years lost…


Other changes

Householder affordability metric

The mooted ‘Householder affordability’ metric is not now being introduced. It was really only needed to stop direct electric and a poor fabric combination being foisted onto an unsuspecting public. With the FEES being retained, that risk is lessened hopefully.

Fuel factors

‘Fuel factors’ are going too. Fuel factors were a bonus added to the TER (Target Emission Rate) of 50% if you installed a heat pump, which was to overcome the fact that the electricity Grid was dirty, although getting cleaner. Now that we are seeing record amounts of renewable energy generation on the UK Grid, electricity is now cleaner in CO2 terms than natural gas and therefore the fuel factor is redundant. This will have an adverse effect on other fuels such as heating oil potentially and that is also seen as a good thing. There was a discussion around bio-LPG having its own figures within SAP, to allow those off the gas/ electricity Grid to have access to a low-ish carbon fuel source. There is a concern that just because your boiler can burn bio-gas, it doesn’t necessarily mean that you will buy the more expensive bio-fuel. Work continues in this area.

Waste Water Heat Recovery Systems

One of the slightly weirder aspects of the response document revolves around Waste Water Heat Recovery Systems (WWHRS). Due to the fact that Government has gone for Option 2, which includes a bit more renewable ‘bling’ (sorry, technologies), WWHRS appears in the Notional House in the Interim version of Part L1A and for the Future Homes Standard, it disappears again. Surely, if it was a great idea and you wanted to see less energy consumed by heating domestic hot water in 2021, the same would apply in 2025?


Thermal bridging

So far, things don’t seem too bad, other than the speed at which all this is happening at. Surely, the Climate emergency is just that, an emergency?

However, things take a turn for the worse when it comes to thermal bridging and it is clear that the Government is torn as to what they should do. For starters, ‘accredited construction details’ are out, which won’t cause a loss of sleep, as they were pretty poor. However, it is not clear how thermal bridging will feature in the 2021 version of Part L1A. The document infers that bespoke thermal bridging calculations will be required for the Future Homes Standard and that a stepping stone to that will be introduced.

In the last iteration of Part L1A, ‘Robust Details’ was pushed as the methodology for thermal bridging, whereby the developer would sign up to a series of thermal bridge designs, pay a fee and a proportion of those perhaps might be inspected on-site to see how successfully they were being implemented. It all rather fizzled out and although several books were produced by various industry bodies, such as the aircrete block industry trade body, it never really gained traction. Its enforcement was non-existent and Building Control Officers had neither the time nor the skills to interrogate the system with any rigour.


Part F: Ventilation: An ill-wind is blowing

In the response to the consultation on Part F, things really do take a turn for the worse and you can see the fingerprints of the housebuilder lobbyists all over it. In a nutshell, it appears that the volume housebuilders are refusing to design a proper ventilation system and, therefore, they want trickle vents and extract fans and leaky homes. You can see their point, so little of their product is designed, so why would ventilation be? Also, their supply chain of subcontractors is, in general, not capable of delivering the airtightness required to make the homes truly energy efficient.

System 3 Passive Stack will disappear from the approved document, mainly on the basis that no one is doing it, it is complicated and is reliant on favourable weather conditions. You can still meet the Regulations with it, but you will have to demonstrate that it is well designed and meets the ventilation requirements. System 1,2,3,4 will disappear and be replaced with system names.

The most comical element of the whole document is where they state the assumption that homes will continue to have an air Infiltration of 0.15 ach in less airtight dwellings as a precaution against too many trickle vents being installed!  Effectively, this is a policy of reducing the need for trickle vents by having leaky buildings. Basically, because the Government is not prepared to acknowledge the need for MVHR or MEV in airtight homes, it is proposing a policy that makes leaky homes more desirable, to minimise the number of trickle vents required. It is a circular argument, aimed at keeping the status quo.

Natural ventilation remains in part F only because that is what everyone uses, not because it is superior.   One glimmer of hope is that Part F will only detail natural ventilation for less airtight homes, such as those designed with an air permeability of more than 5m3/m2.h@50Pa or tested with a result more than 3m3. In other words, natural ventilation is only being proposed for non-airtight homes. This will prevent SAP assessors putting 4m3 into their calculations to get them over the line. The implication is that you might get forced to adopt MVHR or MEV if your air permeability wanders downwards. Another glimmer of hope is that SAP will be tweaked so that when assessing naturally-ventilated homes, no benefit will be derived with an air pressure test result of less than 3m3/m2.h@50Pa. Guidance in Part F will only be given on natural ventilation for leaky homes, but guidance for MEV/ MVHR will be given for any level of air permeability.

There is a lot of nudging here, a bit of a carrot but absolutely no stick, so we are likely to see homes with holes drilled in triple glazed window frames for years to come.

Air Pressure Testing

What are the risks when delivering Passivhaus at scale? Our blog looks at how to manage 5 key areas inc: Communication between separate workstreams; Building services design; Managing the Primary Energy demand; Airtightness; & Site evidence gathering:

There were quite a lot of detailed changes to air pressure testing, the key ones being that every new home will be tested. This is a good thing because currently, it is the only quality test completed on a home. The consultation suggested adding an uncertainty factor to air test results but clearly decided that this was an unnecessary complication and so it has been dropped.

There was a recognition that Pulse Testing of homes was a thing and that it would be allowed in the future. A lot of work has been done by the manufacturer Build Test Solutions to look at the correlation between tests carried out at 4Pa and 50Pa (i.e., blower door tests). The suspicion is that the big boys will adopt Pulse Testing, because it is quick, and continue hacking lumps out of the price and each other. One can only surmise that the independent air testers will not view this as progress.

The bad news is that the notional houses being modelled in both the interim and the Future Homes Standard will feature an air permeability of 5m3/m2.h@50Pa, which can best be described as ‘well-insulated wind-tunnels’.

The document describes the test methodology being changed to reflect CIBSE TM23, it is to be hoped that ATTMA and IATS will be digesting what this means and communicating with their members in due course.

The Performance Gap

The “Performance Gap” gets a few mentions throughout the document and clearly, the perception is that all of this gap happens at the work site and not on the Energy Assessor’s computer. As ever, GIGO (garbage in, garbage out) is really important with all software and assessors are adept at tweaking the U-values and the other parameters within SAP to get the model to pass. It would appear that, save for thermal bridging as discussed above, there will not be any more scrutiny of their inputs.

There is some new emphasis on the need for some photographic evidence to be gathered before the EPCs are issued. This will be pulled together into a BREL report which is quite extensive in nature and will be standardised across all the software providers to assist building control and others better understand the contents. Time will tell how effective this will be and, unless it is policed in a similar fashion to the Certified Passivhaus process, will be ineffectual. How many unscrupulous developers will take a picture of a neighbouring plot because they forgot to take a picture of the detail before it was covered up? It does seem at first glance that the Energy Assessor will be doing more to check the building than the Building Control Officer, which is fine if the rates go up to meet the extra demands and liability all this implies.

It is safe to say that the ‘Future Homes’ standard is not living up to the hype and we all need to be examining wider and more fundamental questions around how we can ensure that all new buildings are designed and constructed to be fit for a zero-carbon future.

Alex Honey Passivhaus Designer EnhabitAlex Honey BEng(Hons) SAP Assessor and Passivhaus Designer

Now Technical Director at Enhabit’s sister company QODA Consulting




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