If you’ve ever wondered what the EnerPHit certification requirements actually demand of a hundred-year-old building, the honest answer is that they ask it to behave like a much younger one: warm, quiet, airtight, and cheap to run.

And it has to do all that without pretending it was born that way.

EnerPHit is the Passive House Institute’s standard for retrofits.

It exists because most existing buildings, however lovingly built, can’t quite reach the full Passive House standard set for new construction.

A basement wall here, an awkward orientation there, and the numbers slip out of reach.

So, the institute created a parallel set of EnerPHit certification requirements with slightly relaxed targets, designed for buildings that already have a past.

On an early episode of Building Green (Episode 8), Barcelona-based Passivhaus specialist Andreu Villagrasa walked through what this looks like in practice, and his framing is a good map for anyone trying to understand the EnerPHit certification requirements before they start.

Inspired by this conversation, today’s post breaks down those requirements, where the difficult points hide, and why the standard is more achievable, and more affordable, than its reputation suggests.

Headline Numbers

At its core, the EnerPHit certification requirements come down to a handful of measurable targets.

A building either hits them or it doesn’t; there’s no rounding up for good intentions.

• Heating demand: For a cool-temperate climate, the energy demand route caps space heating and cooling at 25 kWh per square meter per year, compared with 15 for a new-build Passive House.
• Airtightness: The building must test at 1.0 air changes per hour at 50 pascals (looser than the 0.6 demanded of new Passive Houses, but still far tighter than an ordinary home).
• Ventilation: Mechanical ventilation with heat recovery is mandatory, recovering at least 75 percent of the heat that would otherwise escape.
• Renewables: Depending on renewable primary energy use, the project can certify as EnerPHit Classic, Plus, or Premium.

There are two ways to satisfy the EnerPHit certification requirements: the energy demand method, which judges the whole building against a performance target, or the building component method, which checks each element (wall, roof, window, ventilation unit) against its own benchmark.

The second route is the lifeline for tricky buildings, the ones where orientation or a protected façade makes the whole-building number impossible.

The Question of Continuity

Villagrasa kept returning to one idea, and it sits at the heart of the EnerPHit certification requirements: continuity of insulation.

Insulation only works if it’s unbroken.

Think of it like this: a blanket with a hole in it isn’t really a blanket, right?

In a real building, though, the insulation layer is interrupted constantly … a balcony slab punching through a wall, a steel beam, a door threshold, the junction where a floor meets the façade.

Each break is a thermal bridge, a shortcut that lets heat leak out and, in cold weather, invites condensation and mold on the warm side of the wall.

Villagrasa described designing these points out (slipping a low-conductivity, heat-resistant element into the gap so the thermal path is broken before it can form).

This isn’t a fringe concern whatsoever. It’s actually very important, so much so that the American Society of Heating, Refrigerating and Air-Conditioning Engineers now treats thermal bridges seriously enough that ASHRAE 90.1-2022 sets explicit performance requirements for them, recognition that these small interruptions add up to real, measurable heat loss.

When I was younger I knew someone whose grand old apartment had a cold stripe running down one corner of the living room, right where a concrete column met the outside wall.

Nobody called it a thermal bridge back then; they just moved the armchair.

Five Things the Models Consider

Meeting the EnerPHit certification requirements isn’t guesswork, and thank goodness for that. The requirements run through energy modeling, and Villagrasa described the elements his team interrogates.

Insulation and windows lead the list, but the questions go deeper than “how thick” and “how many panes”:

• Where do the windows point, and how much sun do they get? Orientation changes everything about a building’s heat balance.
• How is the building protected from summer sun? The Department of Energy’s Building America program notes that a correctly sized south-facing overhang can shade a window fully in summer while letting winter sun stream in.
• How is the continuity of insulation maintained across every junction and penetration?
• What does the ventilation system recover, and at what efficiency?
• What windows are specified? ENERGY STAR rates them on U-factor and solar heat gain coefficient, the two numbers that decide how much heat a window keeps in and how much sun it lets through.

There’s a neat detail in the standard that captures this whole philosophy: a window should sit in the same plane as the insulation, so the two form one continuous line rather than handing heat off at the joint.

ASHRAE 90.1-2022 codifies the same principle, asking that glazing align within about two inches of the continuous insulation layer.

Get that alignment right and a thermal bridge simply never forms.

Ventilation Can Pay for Itself

The piece of the EnerPHit certification requirements that surprises people most is the ventilation, and it’s also what Villagrasa was very enthusiastic about.

Seal a building tightly and you can’t rely on drafts for fresh air anymore. The answer is mechanical ventilation with heat recovery.

Stale, humid air is pulled from kitchens and bathrooms; fresh air is delivered to living spaces.

The outgoing warm air hands its heat to the incoming cold air through thin plates, recovering around 75% of it.

You get constant filtered fresh air without throwing your heating out the window.

And it sips energy.

Villagrasa put the running cost of such a system at roughly 50 euros a year, which does not at all reflect the comfort and air quality it delivers. In this case, comfort is not a luxury.

The World Health Organization’s housing guidelines warn that cold indoor temperatures below 18°C are linked to raised blood pressure, respiratory problems, and excess winter deaths. And those are exactly the conditions a well-sealed, well-ventilated retrofit is built to banish.

Why the Standard Bends for Old Buildings

EnerPHit certification requirements are humane in that their standard knows when to flex.

If a heritage authority forbids touching a protected façade, or if a required insulation thickness would make a room unusable, the criteria allow specific exemptions. The building component limits can be exceeded for compelling, documented reasons.

This is the same tension explored in our piece on navigating green building codes, where preservation and performance have to be reconciled rather than pitted against each other. 

It’s also why phased retrofits exist.A building just doesn’t have to meet every target in one expensive push.

The EnerPHit Retrofit Plan lets an owner stage the work over years, each step building toward certification, a logic that complements the envelope-first thinking in our net-zero home guide.

The first deep EnerPHit retrofit in North America, a Minneapolis home known as the MinnePHit House, ended up four to six times more efficient than a conventional new build, proof that the standard works on real, lived-in houses, not just show projects.

The Myth of the Traditional Retrofit

Villagrasa made a pointed observation that is worth some attention here too. The Passive House label, he noted, sometimes gets used to sell grand, high-end houses, a badge for the well-off rather than a tool for everyone. But he’s clear that the math doesn’t have to work that way.

A careful simulation, he argues, can bring the cost premium of building to the standard down to around 10 percent, well within reach of ordinary projects. Looking good in a holistic, low-energy way, in other words, doesn’t have to cost the earth and more.

He’s not against designing for clients with deeper pockets; he simply refuses to accept that high performance and accessibility are opposites.

That stance is meaningful and powerful, not least because the building stock that most needs this work is enormous.

Buildings account for roughly 30% of global final energy consumption, according to the International Energy Agency, and deep energy retrofits can cut a building’s heating demand by two-thirds or more.

The United Nations Environment Programme makes the same calculation, naming retrofits of existing buildings as essential to reaching a decarbonized building stock, since roughly half the buildings that will exist in 2050 are already standing today.

Meeting the EnerPHit certification requirements on an old building is one of the most direct ways an individual owner can take part in that shift, and our smart cities guide shows how those individual upgrades scale into something larger.

Where to Begin

If the EnerPHit certification requirements feel daunting on paper, the reassuring truth is that they reward exactly the kind of careful, considered work that good architecture has always involved: understanding a building, respecting its character, and improving it with intention rather than force.

The healthiest, most comfortable spaces tend to come from that same patient attention. This is a thread we follow in our biophilic design strategies and even in how we approach sustainable workplaces.

If you’re looking at an old building and weighing whether the EnerPHit certification requirements are within reach, we’d love to hear about it.

Tell us about your project through Building Green, and let’s talk through what’s possible, from where to start to what to protect, and how to get there one sensible step at a time.