Passive House

What defines a Passive House?

A Passive House is a building standard that achieves extremely low heating and cooling energy demands through systematic design and construction rigor, not mechanical complexity. The standard is defined by measurable technical criteria: annual heating demand no more than 15 kWh per square metre (often achieved passively through insulation, airtightness, heat recovery, and solar gains), annual primary energy no more than 120 kWh per square metre, and infiltration rate no more than 0.6 air changes per hour at 50 Pa pressure tested via blower door test. In Slovakia, where nearly-zero-energy building (NZEB) standards are legally required for new buildings, a Passive House goes beyond these minimums to deliver both dramatically lower operating costs and exceptional comfort through radiant surface temperatures that feel warm even when ambient temperatures are cool.

What are the core certification criteria?

The Passive House Institute in Darmstadt, which administers the standard, publishes quantitative thresholds that define the category. These criteria are independent of climate zone or energy source, making them universally comparable. Certification requires third-party verification and commissioning. A certified Passive House can claim achievement regardless of whether it is powered by fossil fuels or renewables, though in practice the very low demand makes full renewable supply economically sensible.

Criterion	Requirement	Typical value in Slovakia
Annual heating demand	≤ 15 kWh/m²/year	8–12 kWh/m²/year
Annual cooling demand	≤ 15 kWh/m²/year	3–8 kWh/m²/year
Annual primary energy	≤ 120 kWh/m²/year	60–90 kWh/m²/year
Airtightness (air infiltration)	≤ 0.6 h⁻¹ at 50 Pa	0.3–0.5 h⁻¹ at 50 Pa
Design peak heating load	≤ 10 W/m²	5–8 W/m²

How do the five core principles create this performance?

The Passive House standard is achieved through five interdependent design and construction principles working in concert. No single principle alone produces the result; rather, each amplifies the effect of the others.

1. Superior thermal insulation. Wall assemblies typically feature 200–300 mm of mineral or cellulose insulation, roofs 300–400 mm, and foundation slabs or basements equally thick. U-values for opaque elements must fall below 0.15 W/(m²K), reducing conductive heat loss to near-zero levels. Combined with triple-glazing (U-value typically 0.08 W/(m²K)), the building envelope becomes a nearly impenetrable thermal barrier.
2. Elimination of thermal bridges. Every penetration, corner, and junction must be designed to break conductive pathways. Structural connection details use low-conductivity materials, windows are installed inset from the inner surface of insulation, and balconies (if present) are acoustically and thermally isolated. This prevents local cold spots that would otherwise trigger uncomfortable mould or cold-surface radiation losses.
3. Airtightness of the building envelope. The building must be sealed against uncontrolled air leakage, verified by pressurization testing. A continuous barrier (typically polyethylene or permeable membranes on timber-frame construction) prevents infiltration. Airtightness is critical because uncontrolled air leakage degrades insulation performance and introduces draughts that no amount of heating can overcome comfortably. It is not about hermetic seal for its own sake, but about controlled conditions.
4. Heat recovery ventilation. Because the building is airtight, controlled mechanical ventilation is essential for indoor air quality. An ERV (energy recovery ventilator) or HRV (heat recovery ventilator) supplies fresh filtered air to living spaces and extraction from kitchens and bathrooms, while recovering 75–90% of the heat from exhaust air before it leaves the building. This single system replaces both traditional ventilation and most of the heating system capacity.
5. Optimal utilization of solar and internal gains. South-facing glazing is sized to admit winter sun deep into thermal mass (floor slabs or interior walls), storing warmth and releasing it slowly. Shading, either fixed overhangs or operable blinds, prevents summer overheating. Internal gains from occupants, appliances, and lighting (often 5–10 W/m²) are captured and retained, reducing the need for active heating. The design is passive not because mechanical systems are absent, but because passive mechanisms handle the bulk of load.

How does a Passive House differ from a nearly-zero-energy building?

Nearly-zero-energy buildings (nZEB, or in Slovak context budovy s takmer nulovou spotrebou energie, STN 73 0540-2:2021) are a legal requirement in Slovakia for new construction as of 2021. The nZEB standard defines maximum primary energy consumption (typically 80–100 kWh/m²/year depending on building type and climate zone) and requires renewable energy integration. A Passive House, by contrast, focuses on minimizing demand first, using primary energy as a derived consequence. The distinction is strategic: nZEB is a regulatory floor (what you must achieve), while Passive House is an absolute technical specification (what you can reliably deliver). Every Passive House exceeds nZEB requirements by a wide margin.

Aspect	Passive House	nZEB (Slovak requirement)
Focus	Minimize demand first	Balance demand and renewable supply
Primary energy limit	≤ 120 kWh/m²/year	80–100 kWh/m²/year (varies by type)
Heating demand	≤ 15 kWh/m²/year	No explicit limit (implicit from primary energy)
Renewable energy	Not required by standard; optional	Explicitly required by law
Verification	Third-party institute certification	Energy performance certificate (EPC) and declaration of compliance
Cost premium vs. standard build	8–15% in Slovakia	3–6% in Slovakia (often achievable within standard budgets)

What is the cost impact of Passive House in Slovakia?

A Passive House in Slovakia typically costs 8 to 15 percent more than a standard building that meets only the legal minimum (formerly STN 73 0540-1, now subsumed into the 2025 Building Act and nZEB rules). The premium comprises thicker insulation, triple glazing, continuous air barrier installation and testing, ERV/HRV system, thermal bridge detailing, and commissioning. For a mid-range residential project (1,500 m² net heated area), this translates to approximately 12,000–22,000 EUR in added construction cost. However, the operational savings are substantial: annual heating costs drop by 70–90 percent relative to a standard build, yielding payback periods of 15–25 years depending on energy prices, occupancy patterns, and whether renovations were required to meet nZEB anyway. In new builds, where nZEB is legally mandatory, the incremental cost to reach Passive House from nZEB compliance is only 3–5 percent, because the foundational insulation and airtightness measures overlap significantly.

How does the Passive House standard relate to Slovak building law?

Slovakia's new Building Act 25/2025 Z.z. (in force since 1 April 2025) requires all new buildings and major renovations to meet nZEB criteria. The Passive House standard sits above this legal minimum as a voluntary certification. The law references STN 73 0540-2:2021 (Energy performance of buildings – Part 2: Methodology for energy rating of buildings), which establishes the framework; Passive House certification then provides an independent, internationally recognized verification that the building has been designed and constructed to an objectively higher standard. For passive-house consultants and architects in Slovakia, this means that every new residential project is already pursuing energy performance that overlaps substantially with Passive House targets; the decision to pursue full certification is primarily about documentation, third-party credibility, and the confidence that the design will actually perform as modelled, rather than discovering underperformance after occupation. Passive House Classes allow for variation: Class Plus and Class Premium add renewable energy requirements on top of the energy demand limits, serving projects with further climate or marketing ambitions.