Kym Mead from Mead Consulting explains what Passivhaus certification is, how the process works and why there is a difference between certified Passivhaus buildings and those that just adopt a ‘Passivhaus principles’ approach.
Interview with Kym Mead
Kym Mead initially trained as an architect and then worked at Building Research Establishment (BRE) in the Passivhaus consultancy team. It was here that he got the opportunity to head to the Passivhaus Institut in Darmstadt and become a Passivhaus certifier, one of the UK’s first. As his role required him to do a lot of travelling, when he and his wife started a family he decided to set up his own consultancy MEAD offering architectural services and Passivhaus certification. He soon found himself swamped with certification work and so this became his sole focus.
Passivhaus certification is ‘a helpful audit’
If you are building to Passivhaus standard then Passivhaus certification is part of the process. Kym describes it as a helpful audit that is independent from your design and construction team to ensure that every action you take is working towards the goal of Passivhaus certification. Certifiers are there to provide information about the process and, with a wealth of experience, can be a great support when issues arise as they have most likely come across them before. Certifiers will also be checking the quality of your construction and will ultimately perform an evaluation to check your project meets the Passivhaus standard.
“I always say it shouldn’t be a draconian process from top to bottom, where there’s a big scary certifier saying yay or nay. It should be a helpful process. We all want to get to that same point: that certified building, and we should all work collaboratively together.”
Aim to bring a certifier onto the team early on
By bringing a certifier on board in the design phase of a project any potential issues can be spotted and remedied. The later it is left the more difficult and costly it becomes to change things.
“So if I receive an inquiry, my first question is who’s involved? Is the Passivhaus Consultant involved? Have you run initial checks through the PHPP, carried out the initial energy balance? How’s it looking, how’s it performing? Those kind of questions. And you can gauge from those answers the level of experience within the team. “
Reduce the overheating risk as much as possible
Overheating is defined by the Passivhaus Institut as exceeding 25C for a certain portion of time. The current threshold is for 10% of the year, however Kym would recommend aiming for below the 5% mark in order to make the house as comfortable as possible and to future proof your project.
Overglazing can be an issue
If your design team is new to Passivhaus it is possible they may include too much glass in their designs. This is less of a problem now the Passivhaus market is maturing but was certainly a challenge with some early Passivhaus projects.
Performance rarely improves as the project progresses
Modelling projects in the Passive House Planning Package (PHPP) is another step in the process of designing a Passivhaus. If the initial designs are only just meeting the energy targets (15kWh per m2 per annum) then this could be cause for concern. As a general rule, the performance reduces slightly through the design process. Therefore starting with a conservative goal (for example 12kWh per m2 per annum) will give you some leeway during the build for your performance to fluctuate.
Photographic ‘evidence’ needs to be submitted
Kym explains that if a client requests a site visit he is happy to oblige, but in the majority of cases there is little need. The certification process requires detailed notes, technical data sheets and pictures of the build process which the certifier can examine. A certifier will be looking at the execution of the construction. For example, is the insulation continuous?
Swapping materials last minute could cause a problem
A certifier is also checking that the designs have actually been executed on site. This includes keeping an eye on product changes.
“Contractors may think the lead time on a certain type of insulation is too long, I can get the same thickness of insulation… but the lambda value may be slightly different, which means it’s going to perform slightly differently. So, these things we need to watch out for. We need to make sure that contractors are aware that any changes need to be fed back to the design team.”
Encourage a ‘no blame’ culture
On a construction site things can go wrong. Therefore it’s important to foster an open and honest culture where team members feel safe admitting mistakes. When errors are dealt with at the time it is easier all round. If a mistake is hidden because somebody is worried about getting in trouble then bigger problems can emerge down the line when the performance is checked. This is often related to insulation and airtightness.
Engaging with a certifier keeps you on track
The vast majority of projects that Kym has worked on have gone onto achieve Passivhaus accreditation and the reason for that is that the process acts as a safety net. So when feedback is given and adopted then you move one step closer to certification.
In the unlikely event that a project is not performing it can be investigated.
“There has been the odd occasion where a Passivhaus is not performing as it should do. We’ve gone in and looked at the reasons why. It could be anything from faults with the MVHR, whether that’s human error, installation error, or just manufacturer error, you know, these things happen, we can look at that, and we can go in and fix it.”
Extending a Passivhaus could void the certification
Passivhaus certification may not last forever! A ‘material change of use’ such as extending the property, swapping the heat source or replacing the windows could void the certification.
Therefore careful consideration and analysis is necessary when there is a significant change. Think how it will affect the performance of the house.
Recertification is an option and it is unlikely that you’ll have to go through the full process again. There will just be an administration cost with Passive House Institute.
“There was a project recently and they certified to a Passivhaus. Then a year later they installed some PV. Now they re-certified as a Passivhaus Plus.”
Use the Passivhaus Trust to find a certifier
There are currently 11 Passivhaus certifiers in the UK and you can find their details on the Passivhaus Trust website. Kym says they are all lovely people but may work slightly differently. So have a chat, see who feels right for you and get some quotes. Kym tends to charge according to the size of the building and typically (at the time of releasing this podcast) that might be somewhere between £2000-£3000, for a single, modest-sized dwelling.
Last minute changes could jeopardise certification
The certifiers job isn’t to tell you what to do but to provide all the information you need to make the right decisions. Sometimes you may even choose to abandon the certification path.
“Building houses is never easy. It’s not a sort of practical thing, it’s an emotional thing as well. If it’s your house and you’re investing money into it and you want to make a last minute change, that’s your right. Our job as certifiers and consultants and architects is just to manage that. But if it is going to be an issue, I will explain the issue and if they still want to go on, and it may jeopardise the final pass of our certification, then that’s okay.”
For houses that miss Passivhaus Classic there is also the option to certify to the Low Energy Building Standard.
Adopting ‘Passivhaus principles’ is a gamble
There’s an important distinction to be made between using ‘Passivhaus principles’ versus building to Passivhaus standard. A certified Passivhaus has a strict set of criteria whereas adopting Passivhaus principles is vague – it might be good or it could be miles off.
“I’m always wary of [people] advertising ‘Passivhaus principles’. It feels like people are being a bit misleading. They’re trying to promote themselves on the back of something, but they haven’t actually adhered to the standard anyway. We’ve been doing Passivhaus for long enough that it shouldn’t necessarily be that challenging. If you don’t want to certify a building, you know, that’s up to you. Just don’t say that you’ve adopted Passivhaus principles in your building.”
Passivhaus dwellings may be worth 2-3% more
Although the UK now has thousands of certified Passivhaus dwellings it is still early days. Estate agents may have heard of the Passivhaus standard now but it is fairly rare for them to come onto the market. Therefore the Passivhaus ‘uplift’ is a slight unknown. However, Kym reckons through conversations he’s had that a certified Passivhaus might increase the property value by two to three percent.
A certified Passivhaus ‘does what is says on the tin’
Living in a comfortable house with fresh air 24/7 and low bills is what a Passivhaus delivers. There will be no mould or cold spots. These promises can only be met when a systematic approach has been taken to designing, constructing, commissioning and checking a building. Certification is yet another essential part of getting what you want.
“Passivhaus does exactly what it says on the tin in the sense that if you want a building that performs, it’s a very robust assessment and it will pretty much all the time deliver what you require.”
Find out more
Visit the website of Mead Consulting
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