Greengauge Director Paul Smith shares his thoughts on the PHI Low Energy Building Standard
Discomfort. Cold surfaces. Draughts. Are these not criteria failures? Under one certifiable Passive House Institute (PHI) route, they are simply… allowed.
Welcome to the PHI Low Energy Building standard.
Now. Before you start bashing the keyboard, I am not attacking the Passivhaus Standard. I am describing a reality that designers, certifiers, and clients need to understand, and then make a choice about. Because Passivhaus is a comfort standard. It says so on the tin. Exceptional thermal comfort. No cold surfaces. No draughts. Consistent temperatures room to room, floor to ceiling. It is one of the standard’s founding pillars and, for many clients, the single most compelling reason they commission Passivhaus work in the first place.
So, here is the paradox. A standard defined by comfort, with an alternative certification route that does not require it.
Not ‘relaxes’. Not ‘adjusts for context’. Does not require.
How the PHI LEB standard came to exist
The PHI Low Energy Building standard was introduced in 2015 alongside PHPP 9. The Passive House Institute (PHI) is explicit about what it was designed for. The criteria document and PHI website set out three use cases: small buildings in cold and shaded locations where the Passivhaus targets are genuinely difficult to reach; countries where suitable Passivhaus components are not yet fully available; and buildings that aimed for the standard but missed it due to errors in planning or execution, with a project that fails to meet the airtightness requirement given as the example.
Read that again. Three use cases. One of them is a shading problem. One is a supply chain problem in developing markets. Only one is the near-miss safety net it is most commonly understood to be.
It was not, by any reading of the original intent, designed as a first-choice certification route for new buildings with full access to Passivhaus components in a mature market like the UK.
But this is what we face. Give an inch, take a mile. Once the door is open it’s hard to put the wood back in the hole as the heat rushes out.
The two lines of defence, and what happens when one is removed
Under Passivhaus Classic and EnerPHit Standard criteria, occupant comfort is protected by two distinct layers.
The first is the hygiene criterion, the temperature factor fRsi. Think of this as the mould-prevention floor. It defines the minimum interior surface temperature a component must maintain to prevent condensation forming and mould taking hold. Under PHPP 10, this is calculated project-specifically across all certification routes, based on the actual climate, ventilation rate, and building conditions of the project in question. That replaced the previous fixed climate-zone thresholds and is a refinement, a welcome one. But it remains a hygiene floor, not a comfort ceiling.
The second layer is the comfort criterion, the requirement that interior surface temperatures do not deviate more than 4.2 K below the operative room temperature. This is what prevents cold windows causing radiant discomfort, cold downdrafts, and the creeping misery of a building that technically heats but never quite feels warm. Under Passivhaus Classic and EnerPHit Standard criteria, both layers apply. The hygiene floor and the comfort ceiling work together.
Under PHI Low Energy Building, the comfort criterion does not apply.
The floor remains, project specific. The ceiling is gone. And in practice, project-specific can mean a very long way below what could be considered low risk. IP1/06 sets minimum fRsi thresholds for the avoidance of mould growth and condensation across building types, from 0.75 for dwellings down to 0.30 for storage buildings. A building certified under a Passivhaus standard can, under the Low Energy Building route, produce a project-specific fRsi that sits below the threshold relevant to its own building type without the comfort aspect to protect it. Building Regs should take precedence in that instance, but the risk is in who is looking at what figure, and when, and whether value engineering is trying to shoehorn in inferior components.
The staircase is worth being clear about. Classic: project-specific hygiene floor, comfort ceiling. Fully protected. EnerPHit: project-specific hygiene floor, comfort ceiling still applies. Protected. Low Energy Building: project-specific hygiene floor, no comfort ceiling. Unprotected.
The component paradox
Here is where it becomes particularly difficult to ignore.
PHI still requires that certified components, such as windows and construction systems, meet both a hygiene criterion and a separate temperature criterion. For opaque components in cool-temperate climates the hygiene fRsi criterion sits at 0.70. For transparent components, certification tests both hygiene and comfort performance, and where the comfort criterion is not met, the certificate states what glazing specification is required to compensate. PHI has not moved on this. The component badge still implies a specific level of occupant protection. It is not just an energy performance label. It carries a comfort and hygiene guarantee.
Now specify any component into a PHI Low Energy Building. It does not need to be PHI certified. It does not need to meet the criteria a certified product is held to. The comfort criterion does not apply to the building. The project-specific fRsi may sit far below the threshold that a Passivhaus component was certified to protect against. The PHPP will flag comfort warnings. And under the Low Energy Building standard those warnings can be set aside. Fake news. Disinformation. Because comfort, as the standard is at pains to make clear, is not required.
The occupants can shout from the rooftops that their Passivhaus is uncomfortable. They are not interested in whether it is a Classic, EnerPHit, or Low Energy Building. They just know it does not do what it says on the tin.
The conversation that prompted this
I found myself recently in conversation with a design team who could not recite several critical aspects of the overall criteria, but when the issue of comfort was raised, within a split second they could quote me the exact page number, sentence, and paragraph in the Passivhaus Criteria confirming that the comfort criteria did not apply to this project. This is a Passivhaus Low Energy Building they declared, not a Passivhaus.
The irony was not lost on me.
The loophole exists. Wider stakeholders have found it, read it carefully, understand it, then apply it, not as the safety net it was intended to be, but as a design strategy. Nothing in the PHI Low Energy Building Standard prevents them. But standards set floors, not ceilings. The fact that comfort is not required does not mean comfort does not matter. The physics of cold surfaces, radiant discomfort and draughts does not give two hoots about the chosen certification route on paper before getting to work in the real world. The occupant living with the consequences will not be comforted by a paragraph reference. Passivhaus has built its reputation on a simple, powerful promise: buildings that are genuinely good for the people inside them. Comfort is not a marketing addition to that promise. It is the promise. The PHI Low Energy Building standard, whether intentional or not, offers a lower bar.
It was designed for buildings that nearly made it and fell at the last hurdle, not for designing buildings that threw the jockey off and galloped to the finish line for a failed victory.
So what are we? In defence of discomfort or against it?
Designers, clients, stakeholders and certifiers, which side of the fence do you want to bounce on?
Paul Smith is a Passivhaus Certifier and Director at Greengauge.
