What is Passivhaus: A Complete Guide

What is a Passivhaus?

What is the Background of the Passivhaus?

The Passivhaus concept developed from European low-energy building research in the 1980s. By that period, Sweden and Denmark were already using demanding low-energy standards for new buildings. Researchers wanted to see how far heat demand could be reduced by combining airtight construction, heavy insulation, better glazing, controlled ventilation, and reduced thermal bridges.

The concept itself was developed in May 1988 by physicist Dr. Wolfgang Feist and Swedish building researcher Professor Bo Adamson during Feist’s research stay at Lund University in Sweden.

The first full-scale Passivhaus was then built in Darmstadt-Kranichstein, Germany, in 1991. It consisted of four terraced homes, each about 156 m², designed by architects Bott, Ridder and Westermeyer. The houses were equipped with monitoring equipment so researchers could measure actual temperatures, energy use, ventilation performance, and occupant behaviour.

What Are The Principles of the Passivhaus?

Passivhaus design is built around five core principles:

• High levels of insulation: Walls, roofs, and floors are heavily insulated to reduce heat loss through the building fabric.
• Airtight construction: Gaps and uncontrolled air leakage are minimised. Certified projects are typically tested to a maximum of 0.6 air changes per hour at 50 Pa.
• High-performance windows and doors: These usually use insulated frames and double or triple glazing, depending on the climate and design target.
• Thermal bridge reduction: Junctions around walls, floors, roofs, balconies, windows, and foundations are detailed so heat does not escape through weak points in the envelope.
• Mechanical ventilation with heat recovery: Fresh air is supplied continuously while heat from outgoing stale air is transferred to incoming air, reducing ventilation heat losses.

Passivhaus Standard

The Passivhaus standard is a rigorous, performance-based building standard for energy efficiency. It aims to create buildings that require minimal energy for heating and cooling while providing excellent indoor comfort. The Passivhaus standard is based on five key principles, which translate into specific performance criteria.

Space Heating Demand:

The annual space heating demand must not exceed 15 kWh/(m²a) (kilowatt-hours per square meter per year). In some climates, a peak heat load of 10 W/m² is also considered.

Reasoning: This low heating demand is achieved through high levels of insulation, airtightness, and heat recovery ventilation, minimizing heat loss during colder months.

Space Cooling Demand (in warmer climates):

The annual space cooling demand must not exceed 15 kWh/(m²a), or the peak cooling load should not exceed 10 W/m².  This is achieved through shading, high-performance windows, and potentially night ventilation.

Primary Energy Demand:

The total primary energy demand for all domestic energy uses (heating, cooling, hot water, ventilation, lighting, and appliances) must not exceed 120 kWh/(m²a). This metric accounts for the energy used to produce and deliver energy to the building.

Reasoning: This criterion encourages the use of highly efficient appliances and renewable energy sources.

Airtightness:

The building must have an air change rate of no more than 0.6 air changes per hour (ACH) at 50 Pascals of pressure difference (n50 ≤ 0.6 h⁻¹). This is measured using a blower door test.

Reasoning: Minimizing air leakage reduces uncontrolled heat loss/gain and prevents drafts, improving comfort and energy efficiency.

Thermal Comfort:

The building must maintain a comfortable indoor temperature throughout the year. The operative temperature should be between 20°C and 25°C for at least 90% of the occupied hours.

Reasoning: This ensures a healthy and comfortable indoor environment, preventing overheating in summer and excessive cooling in winter.

What are the Benefits of the Passivhaus?

The main benefit of Passivhaus is that it delivers very low energy demand without sacrificing indoor comfort. Its benefits are tied to measurable building performance:

• Lower heating bills: A certified Passivhaus is designed to need no more than 15 kWh of heating energy per square metre each year. That is far lower than a typical older home.
• Fewer cold spots and draughts: Thick insulation, airtight construction, and high-performance windows help keep walls, floors, and windows warmer inside.
• Fresh air without wasting heat: A mechanical ventilation system brings in fresh air and removes stale air. It also recovers much of the heat from the outgoing air.
• Better indoor comfort: Rooms stay at a more even temperature, so there is less difference between warm and cold areas of the home.
• Lower risk of condensation and mould: Warmer internal surfaces and controlled ventilation help reduce moisture build-up.
• Less uncontrolled air leakage: Passivhaus buildings must usually achieve 0.6 air changes per hour or less at 50 Pa during an airtightness test.
• Better summer performance: Shading, insulation, and careful window design help reduce overheating as well as winter heat loss.

Can You Retrofit Passivhaus Standards to an Existing Building?

Yes. An existing building can be upgraded using Passivhaus principles, but reaching the full Passivhaus standard is often difficult because the building’s orientation, structure, foundations, and existing thermal bridges are already fixed.

For this reason, the Passive House Institute created EnerPHit, its certification standard specifically for existing buildings.

An EnerPHit retrofit typically involves

• Adding high levels of insulation to the walls, roof, and floors
• Replacing old windows and doors with high-performance units
• Improving airtightness around joints, openings, and service penetrations
• Reducing thermal bridges at balconies, floors, roofs, and window connections
• Installing mechanical ventilation with heat recovery
• Upgrading heating, cooling, and hot-water systems where required

Unlike new-build Passivhaus projects, EnerPHit allows slightly higher energy use because existing construction can limit what is technically or economically possible. The current standard can be achieved either through climate-specific energy-demand limits or by meeting specified performance requirements for individual building components.

A retrofit also does not have to be completed all at once. The Passive House Institute allows step-by-step EnerPHit retrofits using an EnerPHit Retrofit Plan, which is useful when windows, insulation, ventilation, and other improvements are being replaced at different stages.

So, an older house can be brought very close to Passivhaus performance, but EnerPHit is normally the more realistic certified standard for an existing building.