Building a Passivhaus: What Does It Actually Change?

Passivhaus has a reputation that runs ahead of the details. Some people imagine a particular look; others think of it as a product, or a type of construction. It is neither. Passivhaus is a performance standard — a defined set of targets for comfort and energy use, with a rigorous method for achieving and checking them.

For anyone designing or building a house, the most useful question is not "what is Passivhaus?" but "what does it change?"

A performance target, not a style

The Passivhaus standard, developed by the Passive House Institute in Germany and promoted in the UK by the Passivhaus Trust, sets targets for how much energy a building needs for heating, how airtight it is, how much primary energy it uses and how comfortable it remains in summer.

For new homes, the Passive House Institute's criteria include a space heating demand of no more than 15 kWh per square metre of treated floor area per year (or a peak heating load of no more than 10 W per square metre), and an airtightness of no more than 0.6 air changes per hour at 50 pascals. Its comfort criteria also limit how often indoor temperatures exceed 25°C.

How a house meets those targets is up to the design team. Passivhaus homes can be timber, masonry, ICF or SIPs; traditional or contemporary; rural or urban.

Modelling from the start: PHPP

Passivhaus design uses the Passive House Planning Package (PHPP), an energy modelling tool that calculates heat demand, overheating risk and other factors based on the building's geometry, fabric, windows, orientation, ventilation and climate.

The significant change is timing. PHPP is most valuable at the earliest design stages, when decisions about form, orientation and glazing are still open. Designers test options and see their consequences — before those decisions are fixed and expensive to change.

Form and orientation

A compact building form, with less external surface area for its volume, loses less heat. That does not mean every Passivhaus is a box, but complexity has an energy cost that needs to be understood and compensated for.

Orientation matters too. Windows facing south can collect useful winter sun; those facing east and west can bring overheating risk. Passivhaus designers often start by considering where the sun is, where the views are, and how the two can be balanced.

Fabric and thermal bridges

Passivhaus buildings typically have high levels of continuous insulation. Just as important is thermal-bridge-free detailing: designing junctions so heat does not bypass the insulation at floors, roofs, openings and structural connections. See Thermal Bridges: The Weak Spots Most Homeowners Never See.

Windows

Windows are often the most expensive and critical component. Passivhaus projects commonly use high-performance, frequently triple-glazed windows, with insulated frames and careful installation. Their position within the wall, the detail around the frame and the balance between solar gain and heat loss are all modelled. See Triple Glazing: Worth It or Expensive Overkill?

Airtightness

The airtightness target for Passivhaus is far more demanding than typical new-build practice. Achieving it requires a continuous airtight layer, designed at every junction, protected during construction and tested — often more than once. See Airtightness: The Invisible Detail That Changes Everything.

Ventilation

Passivhaus homes almost always use mechanical ventilation with heat recovery (MVHR), which provides continuous fresh air while recovering heat from outgoing air. The system is designed, commissioned and documented as part of the project. See MVHR Explained.

Heating

Because heat demand is so low, heating systems in Passivhaus homes can be small. Some use a small heat pump, some a compact combined unit, some heat delivered through the ventilation system, and some a few small radiators. The emphasis is on reducing the need for heat in the first place.

Summer comfort

Passivhaus is often discussed in terms of winter heating, but summer comfort is equally important. The PHPP model assesses overheating risk, and designers use shading, glazing specification, orientation, ventilation strategy and the ability to open windows to manage it. In the UK, new homes must also address overheating risk under Approved Document O.

Construction quality

This may be the biggest change of all. Passivhaus exposes gaps between design and construction. A punctured membrane, a poorly fitted window or a gap in insulation shows up in tests. As a result, Passivhaus projects typically involve:

• detailed drawings for every critical junction
• trades who understand why the details matter
• site supervision focused on airtightness and insulation continuity
• airtightness testing during construction, not just at the end
• commissioning of ventilation systems.

“Passivhaus rewards care. It turns quality from an aspiration into something measurable.”

Testing and certification

Certified Passivhaus buildings are independently checked by an accredited certifier, who reviews the design, PHPP model, product data, construction evidence, airtightness test results and commissioning records. Only buildings that pass can be described as certified Passivhaus.

Principles, "inspired" and certified

It is worth being precise about terminology, because it is often blurred:

• Passivhaus principles — using the ideas of the standard (fabric first, airtightness, thermal-bridge-free design, MVHR) without necessarily meeting the targets.
• Passivhaus-designed or "Passivhaus-inspired" — a building designed with the standard in mind, possibly modelled in PHPP, but not independently certified.
• Certified Passivhaus — a building that has met the criteria and been independently certified.

Each can be a legitimate choice. Certification provides independent assurance and a clear quality framework. Applying principles without certification may suit projects with constraints. The important thing is to be honest about which is which.

Retrofit

For existing buildings, the Passive House Institute's EnerPHit standard sets targets appropriate to retrofit, recognising the constraints of existing structures. Deep retrofit is often planned in stages.

What it means for you

Choosing to build to Passivhaus — or to its principles — means:

1. appointing a design team with genuine Passivhaus experience
2. making key decisions early, informed by modelling
3. investing in fabric, windows and airtightness
4. choosing contractors and trades who can deliver the detail
5. testing and documenting as you go.

Home at Masson Mills is a Passivhaus Centre of Excellence, where you can see the systems and details involved and speak to the people who design and supply them.