Passive House principles, certification criteria and the PHPP
The principles and the numbers that certify them
Passive House design rests on a continuous, thermal-bridge-free envelope with high insulation, airtight construction, high-performance windows, and balanced ventilation with heat recovery; a fifth principle is a minimal, often ventilation-based distribution system. The exam tests whether you can apply the certification limits, not just recite them.
Core certification limits (Classic)
- Heating demand ≤ 15 kWh/(m²a), or heating load ≤ 10 W/m².
- Cooling demand ≤ 15 kWh/(m²a) and cooling load ≤ 10 W/m², with dehumidification limits in humid climates.
- Airtightness n50 ≤ 0.6 h⁻¹.
- Primary Energy Renewable (PER) demand ≤ 60 kWh/(m²a); the older non-renewable primary energy criterion is ≤ 120 kWh/(m²a).
- Overheating: no more than 10 % of hours above 25 °C. Plus and Premium keep the envelope criteria but tighten PER demand (45 and 30 kWh/(m²a)) and require on-site renewable generation (30 and 60 kWh/(m²a) per TFA).
PHPP as the verification tool
PHPP is a steady-state monthly calculation with defined boundary conditions: a specific climate data set, interior temperatures, and Treated Floor Area (TFA) as the reference area. You enter envelope areas, U-values, thermal bridges, window data, ventilation and generation; PHPP returns demand, load, PER and overheating. Certification needs a PHPP file checked by a certifier plus the blower-door result.
Worked example
A 140 m² TFA house: heating demand 13.5 kWh/(m²a), heating load 9.5 W/m², cooling demand 6 kWh/(m²a), n50 = 0.55 h⁻¹, PER 52 kWh/(m²a), overheating 6 %. Every criterion is met, so it certifies as Classic. If demand were 16 kWh/(m²a) but the load 9 W/m², it would still pass, because the two heating criteria are alternatives.
Traps
Mixing gross floor area with TFA distorts every specific value. Treating 15 kWh/(m²a) and 10 W/m² as cumulative rather than alternative. Quoting PE where the current criterion is PER. Using a different climate data set than the certifier's PHPP.