Special Guest Blog featuring Alex Tonge from Ecotest
All new domestic dwellings require an Energy Assessment including an Air Tightness Test under Part L of Building Regulations, but they must also satisfy Part F of the Approved Document associated to Ventilation within buildings. There’s nothing new about this, with Air Tightness Testing and Ventilation requirements being required now for over ten years. However, there’s still confusion about best practice in the industry. Ecotest Director Alex Tonge and Murton & Co Director Jonny Murton discuss how projects can get their energy assessments, air tightness and ventilation right – avoiding unexpected, inconvenient, and expensive headaches.
How does air testing work?
Jonny: Testing the air permeability of a building is a factor that must be considered in the energy assessment of a building. It helps us to determine its energy efficiency and identifies gaps that can be sealed to reduce heating and cooling costs.
Alex: Air tightness testing is a process by which we evaluate the air permeability (air leakages) of a building’s fabric. We do this by using a blower door system to artificially pressurise and/or depressurise the building, but at no risk to the occupants as this is done at very low pressures. The test usually takes place at practical completion because we want to understand the air tightness of a building in a state representative of when it is occupied. However, on projects which place more emphasis on energy efficiency, there are advantages to having more tests to diagnose air leakages throughout the build, so they can be addressed at source. When we take Passivhaus as an example, the guidance recommends three tests throughout the lifecycle of the build but requires at least two for valid certification. Improved air tightness helps to prevent unwanted draughts and infiltration, but it is really important to pair air tightness with an appropriate ventilation strategy that is bespoke to the building. We need to mitigate the potential build-up of pollutants and improve overall indoor air quality. The risks of poor ventilation can result in negative impacts on the health of the occupants and the building itself.
What issues do you come across around air tightness and poor ventilation?
Alex: In energy efficient buildings, and new-builds in particular, you need a combination of air tightness and controlled ventilation. The overall aim is to improve energy efficiency, occupant comfort and produce improvements in indoor air quality. We have a saying in the industry, ‘Build it tight, ventilate right’. Unfortunately, we still encounter consistent issues across both disciplines, such as unaddressed penetrations in the building’s air barrier (commonly the plaster skim) and/or insufficient ventilation provisions, caused by inadequate levels of background ventilation, poor installation of mechanical ventilation systems and a general lack of understanding about how to specify a compliant ventilation system by both contractors and end clients. For too long ventilation has been considered as adequate by merely installing a fan, without considering how that fan needs to perform and what effects its installation will have on its ventilation performance.
Jonny: It’s no good having an airtight building but then not considering ventilation, because you risk a build-up of pollutants and most commonly moisture. We need to control the level of moisture within our buildings. Older buildings naturally let this water vapour permeate through their fabric, but today’s impervious materials combined with improved air tightness don’t do the same job. A good analogy is wearing a non-breathable waterproof jacket without any air vents; put in a bit of exertion and when you take it off, you’ll find the inside is wet because the fabric hasn’t been able to release the water vapour. Buildings are no different.
What ventilation options are available?
Alex: With the emphasis primarily on providing appropriate levels of ventilation to a building, there are a number of solutions available. The most common methods of ventilation in the UK are Natural Ventilation (Background Ventilators with Intermittent Extract Fans), Continuous Mechanical Extraction (MEV) and Mechanical Ventilation With Heat Recovery (MVHR). With the recent amendments to Part F of the Building Regulations, there is now a recommendation that Natural Ventilation is only suitable for ‘less airtight dwellings’. These are designed with an air tightness >5 Air permeability m³(h.m²) and >3 Air permeability m³(h.m²) as tested. Therefore, we would recommend that new builds opt for Continuous Mechanical Extraction systems. These can be centralised, or decentralised units, or a hybrid – essentially a combination of the two. It is still important to note that there is a requirement for background ventilation with MEV systems unless the air permeability is above 5m³(h.m²). However, it is best practice to utilise background ventilators regardless of the air permeability.
With a focus on energy efficiency, Mechanical Ventilation With Heat Recovery (MVHR) is the best option. MVHRs manage the supply of fresh air and the extraction of stale polluted air within a building, passing the warm extracted air across a heat exchanger, recovering the heat, and warming the incoming fresh air. Unlike other methods of ventilation this system recovers the building’s heat, rather than purely extracting it to the atmosphere. Manufacturers report up to 96% heat recovery and this can result in reduced heating bills. Combined with improvements in the air you breathe mean it’s a no brainer.
There’s a caveat though – and I cannot stress this enough – that ventilation systems require a specialised design, specification, installation, and commissioning by a competent person. Without one of these factors, they won’t work properly. Imagine trying to run a marathon in a pair of trainers that are four sizes too small. Engage an expert and heed their advice.
What problems can arise with new builds?
Alex: In our experience, over the last two years we have seen Building Control Authorities increasingly request Regulation 42 compliance (Part F compliance including Ventilation flow rate testing) at sign off. However, every time we inspect a system, we usually find there isn’t enough background ventilation provided alongside intermittent extract fans, resulting in non-compliance. We recently advised one client that their building wasn’t compliant due to this factor. The architect had specified trickle vents across the building and intermittent extract fans located in the wet rooms. However, when the client took on the project management, they hadn’t installed any trickle vents and the fans weren’t performing or in the right locations. With consideration and careful planning, we could have replaced these fans, and improved the installation to ensure flow rate compliance. Although without trickle vents there was no background ventilation provision and a solution to this would have been much more difficult to retrofit. Throughout the project, interested parties hadn’t signposted any issues to the client. The result was an unhappy client who unfortunately was reluctant to make any changes to their new home.
Jonny: If an architect had been involved in the actual project management, then they’re the one who’s made a mistake, but if the client uses a builder to take on the project management – who then took shortcuts – they’ve only got themselves to blame. Clients sometimes say, ‘We’ll manage it from here’ to avoid paying the architect project management fees – and that’s when problems can occur. When ventilation systems aren’t compliant it’s often a failure of many parties. The lesson here is that if you want a compliant ventilation system then you must design it appropriately and if required, provide adequate background ventilation. Remedying inadequate ventilation in buildings can be expensive.
Alex: The implications of not getting ventilation right could go even further than just building damage. If I was someone who had a portfolio of properties that were insufficiently ventilated, I’d be very concerned about causing potential health hazards to the occupants and from a financial standpoint, this failing could be used as the reason for litigation.
What’s your advice for developers?
Alex: Build it tight, ventilate right – but consider your ventilation strategy and other energy efficiency measures at the design stage. Engage experts like Ecotest and Murton & Co to support you in achieving your desired outcomes.