If you're looking into ways to create a more sustainable or eco-friendly home, you've probably come across the term Passivhaus. To put it simply, Passivhaus is a method of creating an energy efficient space that both increases levels of comfort within the home, while also reducing heating and cooling costs.
Despite that fairly simple explanation, creating a Passivhaus home requires a nuanced design process, and adherence to strict building standards. To help you decide if building a Passivhaus is the right move, and to shed some light on the process, we went to the experts.
Here, architect Laura Jane Clark interviews Passivhaus specialist Tara Gbolade of Gbolade Design Studio (opens in new tab), about the ins-and-outs, and specifics of Passivhaus design.
LJC: Is it possible to explain what Passivhaus is in one sentence?
TG: Yes, it is! Passivhaus provides a high level of occupant comfort, while using very little energy for heating and cooling.
But to be fair, I think the answer is more exciting than this. I think if one is really explaining, Passivhaus is the best standard there is for the best quality of life right now. Homes are designed so that we can breathe cleaner air and so there no cold and hot spots in different parts of the house. Challenges such as asthma are vastly reduced in terms of number of attacks because of the superior air quality. It's worth starting from those aspects as well as the fact that, financially, you'll pay the lowest bills with Passivhaus because it is so well insulated.
LJC: Is air tightness fundamental to the Passivhaus build?
TG: It is, air tightness is a critical aspect. We do a blower test to measure air changes per hour, which is slightly different to standard building regulations. The Passivhaus measurement of air tightness is better than where we are with building regulations as it is ten times more strict.
Another really critical aspect between Passivhaus and anything else that there is, even BREEAM, is that the certification for Passivhaus is incredibly stringent. You don’t consider Passivhaus just the initial design stage. You are checking and being checked externally all the way through the build and you have to consider aspects like air tightness, overheating and daylight analysis, etc. Critically, you have a certificate of completion, and they are the best regulations and best form of certification for proving the successful quality of the home.
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LJC: Given these stringent regulations, I assume that it’s not possible to create a successful Passivhaus in a retrofit project?
TG: Actually, you can!
LJC: Oh, that's exciting!
TG: Passivhaus is just for new buildings, but the EnerPhit standard is the Passivhaus for retrofit buildings. So while the standards are not necessarily the same and Passivhause is more stringent, you can get certification for parts of a retrofit Passivhaus. The EnerPhit standard is the next best thing in effect. In fact, local authorities have committed to a degree to reaching those types of standards with their existing housing stock. So the answer is yes. It's not as good as Passivhaus but it's close enough.
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LJC: One of my reservations with Passivhaus is that you aren’t able to open a window given the strict air tightness requirements. Is that just a myth or is a Passivhaus home designed to be completely sealed?
TG: You can definitely open your windows! You just open the window as you would normally. It is a common myth that you can't open your windows. The point is though, you would not need to open your window to control your environment, i.e. to cool it down. As Passivhaus has been designed at the design stage and certification stage to ensure optimal internal thermal comfort, you would not need to open windows to cool spots down as you ordinarily would do in a normal house.
Integral to Passivhaus is the MVHR system. That is the Mechanical Ventilation with Heat Recovery system. It means that the cold, fresh air outside entering your building is heated or cooled depending on what is needed and then distributed in different parts of the home. So you already have fresh air coming in, just not through the windows. That's why in Passivhaus the windows don’t need trickle vents. But the vents that are part of the MVHR system circulating fresh air into the home have to remain open otherwise the air goes stale and mould can form. So it is critical that the occupants are aware of how the Passivhaus system works and the internal vents are part of the controlled system, and even though we are so used to installing windows with trickle vents, they are not needed at all.
LJC: So, in terms of cost, if a standard build is approximately £1,600 per meter square including VAT to a plaster finish then what is the extra over to build the equivalent to Passivhaus standard?
TG: This is a very good question and it’s hotly debated. It roughly sits about 6-to-8 per cent percent higher for a single home.
LJC: Oh wow! Is that all?
TG: That always has to be put in context, particularly when it's your own home. How long the payback takes needs to be considered. Will it take 10 years or 20 years for it to pay for itself and the added benefit of not paying high energy bills, so for a typical Passivhaus you could expect your energy bill to be around £120 per annum.
LJC: And my last question is, if you were going to undertake a self build, would you go the Passivhaus route?
TG: No brainer! Yes absolutely. Interestingly, right now we're retrofitting our home. Although we can't afford everything that we want to reach the standards, we still have the conversation of how much insulation to install and what standards and we try to meet. And if we're building a new house, like no brainer, Passivhaus is just absolutely amazing.