Passive House — Passivhaus in the original German — is a voluntary, performance-based standard for buildings that need almost no active heating or cooling. It was formalised by Dr Wolfgang Feist and the Passivhaus Institut (PHI) in Darmstadt in the early 1990s, drawing on earlier superinsulation and low-energy research from North America and Scandinavia. The first certified dwellings, built in Darmstadt-Kranichstein in 1991, are still performing to specification more than three decades later — a level of long-term, monitored evidence almost no other building standard can claim.
Crucially, Passive House is not a construction system, a proprietary product or a 'look'. It is a set of physics-based performance targets, verified by calculation (PHPP) before construction and by on-site measurement (the blower door test) after it. A building either meets the numbers or it does not. That measurability is exactly why it matters to a building-performance consultancy: it replaces opinion and marketing with evidence.
The Passive House performance targets
Classic Passive House certification for new build requires a building to meet hard, measured limits. These are the figures every Passive House Designer works to from the first sketch:
| Metric | Limit | What it controls |
|---|---|---|
| Space heating demand | ≤ 15 kWh/m²·yr | Annual energy needed to keep the building warm |
| Heating load (alternative route) | ≤ 10 W/m² | Peak heating power — small enough to heat via the supply air |
| Airtightness | ≤ 0.6 ACH₅₀ | Uncontrolled air leakage through the envelope at 50 Pa |
| Primary Energy Renewable (PER) | ≤ 60 kWh/m²·yr | Total renewable primary energy for all building uses |
| Overheating frequency | ≤ 10% of hours > 25 °C | Summer comfort / overheating risk |
Treated Floor Area (TFA) — the Passive House internal floor-area metric — is the denominator for these figures. It is calculated to a strict PHI methodology and is typically smaller than gross internal area, which is one reason naïve back-of-envelope comparisons with SAP figures can mislead.
Fabric first: the principle behind the numbers
Passive House achieves these targets through a 'fabric-first' strategy: get the building envelope right before you specify any mechanical system. A Passive House works because heat losses are driven so low that the small remaining demand is trivially met. The five interdependent principles — continuous insulation, thermal-bridge-free detailing, an airtight envelope, high-performance glazing, and mechanical ventilation with heat recovery (MVHR) — are explored in depth in the dedicated articles below.
The order matters. A heat pump bolted onto a leaky, poorly-insulated house is treating the symptom; a Passive House removes the demand first, so whatever heat source remains is small, cheap to run and comfortable. This is precisely the logic we bring to retrofit — reduce the load before you size the plant.
It is fundamentally about comfort and health
The targets are not abstract energy bookkeeping — they are derived from human thermal comfort. PHI set the insulation and glazing standards so that internal surface temperatures stay close to air temperature (no cold walls, no radiant asymmetry, no draughts), and so that no internal surface falls below the dewpoint margin that triggers condensation and mould. A Passive House is specified to be comfortable and moisture-safe; low energy use is the consequence, not the sole aim.
- Even internal surface temperatures — no cold external walls or window reveals.
- No draughts, because the envelope is airtight and ventilation is delivered gently and deliberately.
- Continuous filtered fresh air via MVHR — measurably lower CO₂, humidity and particulates.
- Quiet — a well-insulated, airtight, triple-glazed envelope is also an excellent acoustic barrier.
- Durable — surfaces kept above the dewpoint margin are not at risk of surface condensation or mould.
Certification classes: Classic, Plus and Premium
Since 2015, PHI has used a renewable-primary-energy framework (PER) with three classes that reward on-site renewable generation:
| Class | PER demand | On-site renewable generation |
|---|---|---|
| Classic | ≤ 60 kWh/m²·yr | Not required |
| Plus | ≤ 45 kWh/m²·yr | ≥ 60 kWh/m²·yr (referenced to footprint area) |
| Premium | ≤ 30 kWh/m²·yr | ≥ 120 kWh/m²·yr (referenced to footprint area) |
All three classes share the same uncompromising fabric requirements (≤ 15 kWh/m²·yr heating demand, ≤ 0.6 ACH₅₀ airtightness). The classes differ only in how much renewable energy the building generates and uses. This matters: you cannot 'buy back' a leaky envelope with solar panels — the fabric targets are non-negotiable in every class.
What about existing buildings? (EnerPHit)
Most of the UK's homes are already built, so the larger opportunity is retrofit. PHI's EnerPHit standard applies Passive House principles to existing buildings, where party walls, geometry and conservation constraints make the new-build targets impractical. EnerPHit relaxes the heating-demand limit (typically ≤ 25 kWh/m²·yr in a cool-temperate climate) while keeping the same uncompromising attention to airtightness, thermal bridging, ventilation and — most importantly — moisture safety. We cover this fully in the dedicated EnerPHit article.
Common misconceptions
- "You can't open the windows." You can — MVHR simply means you don't need to for fresh air. Comfort doesn't depend on keeping them shut.
- "It's only for new builds." EnerPHit applies the same physics to existing buildings and is arguably more valuable there.
- "It's about technology." It's the opposite — the technology (the heat source) is minimised because the fabric does the work.
- "It overheats in summer." Overheating is an explicit certification criterion (≤ 10% of hours over 25 °C); a properly-designed Passive House is modelled and shaded to prevent it.
- "It's prohibitively expensive." The fabric costs more; the heating system and running costs are dramatically smaller. On a whole-life basis the gap narrows or closes.