# Passive House Standard ## Table of Contents - [[#Overview]] - [[#History and Origins]] - [[#Core Performance Criteria]] - [[#The Five Principles of Passive House Design]] - [[#Superinsulation]] - [[#Thermal Bridge Free Construction]] - [[#Airtight Building Envelope]] - [[#Mechanical Ventilation with Heat Recovery]] - [[#High-Performance Windows and Doors]] - [[#Passive House Planning Package PHPP]] - [[#Certification Classes]] - [[#EnerPHit Standard for Retrofits]] - [[#Climate-Specific Considerations]] - [[#Design Process and Integration]] - [[#Cost Implications]] - [[#Comparison with Other Standards]] - [[#Practical Notes for Architects]] - [[#References and Standards]] --- ## Overview The Passive House (Passivhaus) standard is a rigorous, science-based energy performance standard for buildings that achieves dramatic reductions in heating and cooling demand through a fabric-first approach. Developed in Germany, it is widely recognised as the most demanding voluntary energy standard for buildings globally. A Passive House is not a brand or a construction system but a performance-based standard that can be achieved with any construction method, in any climate zone, and for any building typology. --- ## History and Origins - **1988**: Concept developed by Dr Wolfgang Feist (Germany) and Professor Bo Adamson (Sweden). - **1991**: First Passive House built in Darmstadt-Kranichstein, Germany (terraced housing). - **1996**: Passivhaus Institut (PHI) founded in Darmstadt by Dr Feist. - **2003**: PHPP software released for energy balance calculations. - **2015**: Passive House Classic / Plus / Premium tiers introduced to incorporate renewable energy generation. - **Present**: Over 60,000 certified Passive House buildings worldwide across all climate zones. --- ## Core Performance Criteria The Passive House standard defines the following quantitative thresholds: | Criterion | Requirement | |----------------------------------|--------------------------------------| | Specific space heating demand | ≤ 15 kWh/(m²a) | | Specific space cooling demand | ≤ 15 kWh/(m²a) | | Heating load | ≤ 10 W/m² | | Cooling load | ≤ 10 W/m² (sensible + latent) | | Airtightness (pressurisation test)| n50 ≤ 0.6 ACH at 50 Pa | | Primary energy demand (PER) | ≤ 120 kWh/(m²a) | | Overheating frequency | ≤ 10% of hours above 25°C | These criteria are verified through the [[#Passive House Planning Package PHPP]] energy balance tool, not through dynamic simulation alone. --- ## The Five Principles of Passive House Design ### Superinsulation The [[Building Envelope Fundamentals]] must achieve exceptionally low U-values to minimise transmission heat losses: - **Walls**: Typical U-values of 0.10–0.15 W/(m²K) - **Roofs**: Typical U-values of 0.08–0.12 W/(m²K) - **Floors**: Typical U-values of 0.10–0.15 W/(m²K) Insulation thickness varies by climate zone. In Central European climates, wall insulation thicknesses of 250–400 mm are common. The key metric is not insulation thickness alone but the achieved U-value of the complete assembly including fixings and junctions. ### Thermal Bridge Free Construction Thermal bridges (linear and point) must be minimised to the extent that they become negligible in the energy balance: - **Target**: Linear thermal transmittance ψ ≤ 0.01 W/(mK) for all junctions. - Critical junctions include wall-to-floor, wall-to-roof, window-to-wall, balcony-to-slab, and penetrations. - Thermal bridge analysis is performed using 2D/3D finite element software (e.g., THERM, Flixo, AnTherm). - Structural thermal breaks (e.g., Schöck Isokorb) are used at cantilevered elements. - Continuous insulation envelopes wrapping the entire heated volume are essential. ### Airtight Building Envelope An airtight layer must be continuous around the entire thermal envelope as described in [[Air Barrier Systems]]: - **Requirement**: n50 ≤ 0.6 air changes per hour at 50 Pa pressure difference. - The airtight layer is typically on the warm side of the insulation (vapour control layer in cold climates). - All penetrations (services, structural elements) must be sealed with certified tapes and grommets. - Airtightness is verified by a blower door test (EN 13829 / ISO 9972, Method A). - An airtightness concept drawing must be produced showing the continuous line of the airtight layer on every section and detail. **Practical formula for air leakage**: ``` q50 = V̇50 / AE ``` Where q50 is the air permeability rate (m³/h·m²), V̇50 is the air volume flow at 50 Pa, and AE is the envelope area. ### Mechanical Ventilation with Heat Recovery Since the building envelope is highly airtight, controlled ventilation is mandatory to ensure indoor air quality: - **Heat recovery efficiency**: ≥ 75% (PHI certification requires ≥ 75% effective heat recovery rate). - **Electrical efficiency**: Specific fan power ≤ 0.45 Wh/m³. - Supply air is delivered to living spaces and bedrooms; extract air is drawn from kitchens and bathrooms. - Summer bypass mode allows free cooling when external temperatures are favourable. - Frost protection via earth-to-air heat exchangers or electric pre-heaters prevents icing of the heat exchanger. - MVHR units must be PHI-certified for guaranteed performance. ### High-Performance Windows and Doors Windows are the weakest thermal element and must be carefully specified: - **Installed window U-value (Uw,installed)**: ≤ 0.85 W/(m²K) for Central European climates. - **Glazing**: Triple glazing with Ug ≤ 0.5–0.7 W/(m²K), g-value (SHGC) of 0.50–0.62. - **Frame**: Thermally broken or insulated profiles with Uf ≤ 0.80 W/(m²K). - **Spacer bars**: Warm-edge spacers (ψg ≤ 0.035 W/(mK)). - **Installation**: Positioned within the insulation zone, with insulated reveals. - Window orientation and shading must be optimised for net solar gain in heating-dominated climates. --- ## Passive House Planning Package PHPP The PHPP is the official design and verification tool for Passive House projects: - Spreadsheet-based steady-state energy balance tool (Microsoft Excel). - Calculates heating demand, cooling demand, primary energy, overheating risk, and summer comfort. - Inputs include geometry, U-values, thermal bridges, ventilation rates, internal gains, shading factors, and climate data. - Uses monthly energy balance method (derived from EN 13790). - Climate data sets are available for locations worldwide from PHI. - **designPH** is a companion SketchUp plugin for 3D geometry input into PHPP. - PHPP results form the basis of Passive House certification submissions. --- ## Certification Classes Since 2015, PHI offers three certification tiers based on renewable energy generation: | Class | PER Demand | Renewable Generation | |---------------|----------------------|------------------------------| | Classic | ≤ 120 kWh/(m²a) | No requirement | | Plus | ≤ 90 kWh/(m²a) | ≥ 60 kWh/(m²a) | | Premium | ≤ 60 kWh/(m²a) | ≥ 120 kWh/(m²a) | Plus and Premium tiers integrate renewable energy generation (typically [[Solar Photovoltaic Systems]]) to move towards [[Net Zero Energy Buildings]]. --- ## EnerPHit Standard for Retrofits EnerPHit provides a realistic retrofit standard acknowledging the constraints of existing buildings: | Criterion | EnerPHit Requirement | |------------------------------|-----------------------------------| | Specific heating demand | ≤ 25 kWh/(m²a) | | Airtightness | n50 ≤ 1.0 ACH at 50 Pa | | Component method (alternative)| Meet component U-value criteria | EnerPHit allows either a whole-building energy demand approach or a component-by-component approach where each building element meets specified maximum U-values. This flexibility accommodates phased retrofit programmes. --- ## Climate-Specific Considerations The Passive House standard is applicable across all climates, with adapted strategies: - **Cold climates**: Emphasis on insulation, airtightness, and solar gain optimisation. Higher insulation thicknesses required. - **Temperate climates**: Balanced heating and cooling approach. Standard insulation levels. - **Hot-humid climates**: Emphasis on cooling demand, dehumidification, solar shading, and moisture management. - **Hot-arid climates**: Night cooling, thermal mass, shading, and evaporative cooling strategies. PHI provides climate-specific PHPP data sets and adapted criteria for cooling-dominated regions. --- ## Design Process and Integration 1. **Concept stage**: Establish compact building form (low surface-to-volume ratio), optimise orientation, and define insulation strategy. 2. **Developed design**: Prepare PHPP model, iterate envelope specifications, select MVHR system, and resolve thermal bridges. 3. **Technical design**: Produce airtightness concept drawings, detail all junctions, specify certified components. 4. **Construction**: Quality assurance on site, interim blower door tests, thermographic surveys. 5. **Commissioning**: Final blower door test, MVHR balancing, handover documentation. --- ## Cost Implications - Typical cost premium for Passive House in Central Europe: 5–15% over standard construction. - Premium decreases with designer and contractor experience. - Reduced mechanical systems (no conventional boiler/radiators) offset envelope costs. - Operational energy savings of 75–90% compared to standard buildings. - Payback periods are typically 10–20 years depending on energy costs and climate. --- ## Comparison with Other Standards | Aspect | Passive House | [[Net Zero Energy Buildings]] | Building Regulations Part L | |--------------------------|---------------------|-------------------------------|-----------------------------| | Heating demand | ≤ 15 kWh/(m²a) | Varies (net zero balance) | ~40–60 kWh/(m²a) | | Airtightness | n50 ≤ 0.6 ACH | No specific target | ≤ 5–10 m³/(h·m²) at 50 Pa | | Verification tool | PHPP | Various simulation tools | National calculation methods| | Renewables required | No (Classic) | Yes (to offset demand) | Encouraged | | Certification | PHI or affiliates | Varies by definition | Regulatory compliance | --- ## Practical Notes for Architects - Begin PHPP modelling at RIBA Stage 2 to inform massing and orientation decisions. - Aim for surface-to-volume ratios below 0.7 m⁻¹ for efficient form. - Coordinate the airtight layer with the structural engineer and M&E consultant from Stage 3. - Specify only PHI-certified components (windows, MVHR units, insulation systems) for certified projects. - Allow for 2–3 interim blower door tests during construction to identify and repair defects. - Document all thermal bridge details with PSI-value calculations for the PHPP submission. - Consider the EnerPHit pathway for heritage and conservation projects where full Passive House is impractical. --- ## References and Standards - Passive House Institute, *Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard* - Feist, W., *Passive House Planning Package (PHPP)* — Version 10 - EN 13790: Energy Performance of Buildings — Calculation of Energy Use - ISO 9972: Thermal Performance of Buildings — Determination of Air Permeability - [[Net Zero Energy Buildings]] - [[Building Envelope Fundamentals]] - [[Air Barrier Systems]] - [[Energy Modeling for Buildings]] --- #sustainability #passivhaus #passivehouse #energyefficiency #fabricfirst