Webinar spotlight: navigating ventilation standards

CABE webinar Wednesday presenter Ruth MacEachern advises building control, building surveyors and building engineers across the home nations on the latest developments regarding the different regulatory standards that govern ventilation, including how to prepare for proposed changes. She also looks at the most common ventilation systems used and how the Passivhaus model could, where appropriate cost-wise, offer a common, best practice, approach. 

The current UK government, like its predecessor, has advocated a legislative framework to improve the energy efficiency and reduce the carbon emissions of new homes and non-domestic buildings. 

In line with the statutory powers given to the devolved nations, separate consultations have taken place on what have been differing approaches as well as the timetable for when the relevant regulations will come into force. 

While England and Wales have adopted a similar approach, Scotland has differed and has also been far more ambitious, in part because it has a shorter timescale to achieve its net zero target (by 2045 rather than 2050). In Northern Ireland, meanwhile, progress has partly been hampered due to the assembly’s suspension although a target of 2050 is in place for net zero.  

Like many legislative ambitions, the regulatory launch dates continue to slip. According to Ruth MacEachern, Product Manager at EnviroVent, who delivered a webinar on the Future Homes and Building Standards for CABE in December (see below), the final Future Homes Standard should land in England before late March (originally it was due early 2025). In Wales, its introduction is most likely to be late 2026, if not early 2027, and in Northern Ireland it will be much later. 

Scotland, on the other hand, already deploys its New Build Heat Standard, which is part of the Scottish government’s broader “Housing to 2040” strategy. Ruth says this regulatory tool, which uses zero carbon emission systems to, for example, lower energy performance certificate levels, has shaped the content of England’s warm homes plan, published in January. 

Again, while there is still uncertainty around when the regulations will apply in the respective home nations, Ruth reasons that affected parties will be given a 12-month grace period to prepare, not least because significant work will be required, for example, to improve expertise and skills.

Originally, Part F of the Building Regulations in England and Wales and section 3.14 of the Technical Handbook in Scotland only applied to new builds. However, the first uplift in the Future Homes and Building Standards introduced a retrofit section into the approved documents which covers three key ventilation options.

The most commonly used ventilation systems

The first is natural ventilation with intermittent extract fans and background ventilators. This system, she explains, comprises basic on/off bathroom fans that can be activated and deactivated by a light switch or similar.  

"Because they’re only on and off at certain times, you must have some form of background ventilation, such as trickle vents in your windows,” she says. “There is a reliance on natural ventilation to keep these fans going because they’re only installed in the wet rooms."

Previously, in England and Wales, this ventilation system could be fitted into any property regardless of leakage rates. However, in Scotland, which, in Ruth’s words, was "ahead of the curve", the government there added a requirement into the Technical Handbook that this type of ventilation system should only be used in the most drafty/leaky properties which has since been adopted by England and Wales. 

"With the higher air permeability level, this makes sense because you need that additional airflow for the property to be effectively ventilated," she comments. However, Ruth points out that it can be very hard to achieve compliance with this requirement and this "natural ventilation" system is only really suitable in retrofits if an existing fan needs replacing due to high background ventilation requirements.

The second ventilation system is continuous mechanical extract, which comprises two different types – centralised mechanical extract ventilation (c-MEV) and decentralised mechanical extract ventilation (d-MEV). Previously, these two types of continuous mechanical extract were often considered together but due to increased use of d-MEV in place of intermittent extract fans for compliance, Ruth suggests separating them.

"C-MEV commonly sits in a loft space or a cupboard and has ducting running off it that goes into the wet rooms. Valves in the ceiling extract moisture from each wet room into a single unit, which is expelled into the atmosphere. However, if ducting isn’t an option, you can use a d-MEV. These look a bit like the intermittent fans but are continuously running."

For anyone involved in retrofit work who is looking to replace intermittent fans with a better ventilation option, d-MEVs offer a good upgrade, she continues, because they are roughly the same size as the fans and can fit over the top of a previous installation.

"You do still need a little bit of background ventilation because they only cover wet rooms,” she advises. “But you only need roughly one or two trickle vents per window and it’s only the habitable rooms that you need those trickle vents in. It’s much more manageable."

Ruth observes that, with a tightening in the regulations, many developers, including the National House Builders, have moved away from using intermittent fans and increasingly deploy d-MEVs.

"Another reason why it’s good to split c-MEVs and d-MEVs is that Part L of the Future Homes Standard looks at energy efficiencies," she advises. 

"It refers to what’s called a notional or typical dwelling and efficiency levels that should be achieved including the use of solar, the air tightness level, the levels of heat transfer through windows, flooring and all the scoring around that – and part of a new proposal shows d-MEVs as a secondary ventilation strategy in addition to intermittent fans."

The third and final ventilation system is continuous mechanical ventilation with heat recovery, otherwise known as MVHR, which in Scotland is referred to as mechanical extract and supply ventilation. 

"This is mandatory for Passivhaus standards, but it has to be listed on their website; you can’t just design any MVHRs because there are certain stipulations," she explains.

Ruth adds that there are centralised and decentralised MVHRs, but the centralised version is the one that is written into Scotland’s Technical Handbook and Part F of the Building Regulations for England and Wales.

Typically, an MVHR comprises a central unit, which can be fitted in a loft space, particularly if it is insulated, or alternatively a storage or plant room or large cupboard. Ruth says an MVHR often looks like a Lego brick with four spigots on the top. 

"You have ducts into each of your wet rooms like you would do with a centralised mechanical extract system that runs back to the central unit," she explains. 

"However, the unit also supplies filtered air via ducting runs to your habitable rooms like the living room and bedrooms. Inside the central unit is a heat cell and what it does is really clever. You take the moist, stale air out of the wet rooms, your kitchen and bathroom and while the air goes into the atmosphere, the recovered heat is retained in the cell and then circulated around the property alongside the supplied air."

It’s a win-win because this approach improves energy efficiency and also helps to reduce heating bills. 

"As a result of that being both extract and supply, you do not need any background ventilation. You don’t have to have trickle vents," she continues.

Ruth is advocate of the MVHR but recognises that many people are concerned about the high upfront costs for installation. 

All three of these options are listed in the approved documents and the Technical Handbook as the recommended systems to use. However, both documents also state that alternative systems can be deployed if the person installing them can prove they meet the overarching requirements of the relevant standard in each home nation, notably the airflow rates listed. Two common alternatives, she adds, are single room heat recovery systems and positive input ventilation. 

A common approach to cutting carbon emissions

With each of the home nations running to different regulatory timetables and other UK territories like Guernsey and Jersey watching to see what approach might best fit their own requirements, Ruth believes developers could be far more proactive in reducing carbon emissions in new builds (and retrofits) by adapting the German Passivhaus standard, albeit where costs permit. 

As she explains, the overarching principles of the Passivhaus model are thermal efficiency and comfort and while the long-term returns from installing features like underfloor heating, glazing and wall insulation include excellent ventilation and very low energy bills, the extortionate outlay for the materials has minimised the uptake of this approach. 

"Passivhaus is never done on mass. Typically, it is very small developments,” she explains. “If you go directly with the Passivhaus standard, you need to follow the components listed on the Passivhaus website, so you can only use certain recovery units, certain energy products and certain windows, which have all got particular gradients. Quite often the windows are aluminium and very airtight."

If developers are already struggling to absorb the costs of shifting from deploying intermittent fans, which can cost around £20-£30 at outlets like B&Q, to a d-MEV that costs around £60-£70, then it is unlikely many can afford to adopt the Passivhaus approach. However, Ruth argues that there are huge long-term benefits for those who are prepared to absorb the high initial costs involved. 

In Scotland, the government is proactively pushing this approach. “The most up-to-date information that I found is that at some point, the Passivhaus standard will become a requirement for new builds,” notes Ruth. 

"How far they’re going to go in parallel with the German standard is anyone’s guess. But it will be optional up to a point. Sometime in 2028, it will become mandatory."

Planning for the future

With so much uncertainty over the regulatory timetable governing the various standards, Ruth’s advice to readers is to look through the relevant consultation documents for their home nation and mentally prepare for the new requirements that will come into force once the grace period ends.

"In England and Wales, they’ve put the consultations on each nations’ respective websites and highlighted what has changed and what’s being proposed in a different colour," she says.  

"Outside of that, when it comes to ventilation systems, we are moving towards what we call a systems focus so approaches like MVHR. The first part of the Future Homes Standard in England and Wales brought in approved document O, which, like section 3.28 in the Technical Handbook in Scotland, considers issues like overheating. It’s important to consider that going forward."

Finally, she advises readers to monitor developments around Awaab’s Law, which has already been introduced in England via the Social Housing (Regulation) Act. In Scotland and Wales separate parliamentary bills will be submitted this year, in April and October, respectively.

This law, which came into force in England in October last year, requires social landlords to deal with damp and mould in housing stock promptly to protect tenants. The legislation is named after two-year-old Awaab Ishak, who died from mould exposure. 

Watch Ruth’s CABE webinar Wednesday presentation below.