Passive House: Introduction and Key Concepts 9/9/25

Passive House introduction and speaker background

• Lecturer: Elrond Burrell, introduces the Passive House (Passivhaus) standard and its application in NZ and globally

• Context: Break from materials focus to explore a different, yet related, topic in building design and performance

• Speaker background: architect with ~30 years practice, including UK and NZ; worked in large and small practices, government adviser for architecture and design; joined academia recently; board member of the Passivas Institute NZ (education and promotion of Passive House)

• Course context: Part of a series (SARC 122) and relates to Passivhaus as a performance standard for buildings

What is Passive House (Passivhaus)?

• A standard for buildings, not a green rating system

  • It sets specific performance metrics to be met, based on how a building will perform when finished

  • Unlike ratings like HomeStar, Green Star, BREEAM, LEED, you don’t pick which parts to do; you must meet the standard consistently

• Etymology and naming

  • From German: “Passive House” (the term “house” in German is broader, originally “Passivhaus”)

  • In NZ, Maori name Forre Kourou translates to a concept like “house of vitality/energy” (described as a nicer poetic equivalent)

• First Passive House (historical anchor)

  • Built in 1991 in Cranachstein, Germany

• Global uptake (as of 2025)

  • Approximately $4{,}500{,}000 ext{ m}^2$ of certified useable floor area worldwide

  • NZ as of 2025: about $165$ certified units (mostly houses, some apartments, one office)

• Notable scale of projects

  • Passive House can apply to single houses, multi-unit residential, offices, schools, retrofit projects, and even large towers

  • Examples shown globally: office in Boston (largest certified passive house office at the time), schools, social housing, indigenous community housing, and modular builds

• NZ-specific context and milestones

  • NZ’s first Passive House in 2012: a single-family home in Auckland

  • Notable NZ projects: Toi Ora co-housing in Dunedin (Otago) – 21 houses on a disused school site; Kainga Ora – 18 social housing units in Auckland (state-funded project)

  • New Zealand has also seen office projects and other housing more recently; climate and geography influence design decisions

Core aims of the Passive House standard

• Two central questions the standard answers

  • How can buildings be healthy and comfortable while using as little energy as possible?

  • How can we close the performance gap between predicted and actual performance observed in buildings?

• Health, comfort, and energy use

  • Health: Daylight, good indoor air quality, adequate humidity control, appropriate acoustics

  • Comfort: Thermal comfort, radiant/air temperature balance, avoidance of drafts and cold surfaces

  • Affordability: Energy costs kept low while delivering high performance

• Comfort definition and climate specificity

  • Comfort is partly subjective; well-being depends on environmental conditions and individual preferences

  • WHO guidance and ISO 7730 concepts underpin healthy and comfortable indoor environments

  • WHO temperature guidance (well-insulated, well-heated spaces for most occupants): typically a range around $18^ ext{°}C$ to $24^ ext{°}C$, depending on vulnerability (e.g., elderly, children) and clothing

  • Passive House is climate-specific: what you must do to meet the standard depends on local climate to ensure well-being and energy performance

Design principles and building physics

• Non-prescriptive design: form, materials, and construction methods are not dictated; the standard defines performance outcomes, not a recipe

• Five core characteristics (design factors)

  • Envelope and continuity: airtight, continuous insulation without breaks or bridging through structure

  • Thermal envelope: prevents heat loss and condensation; controls water, air, and vapor movement

  • Windows and doors: key roles in heat transfer, daylight, ventilation, and comfort

  • Ventilation: balanced heat-recovery ventilation providing continuous fresh air

  • Energy modelling: to predict and verify performance, linking design decisions to outcomes

• The building envelope as the primary control layer

  • Insulation continuity is critical to avoid thermal bridges, which waste energy and cause comfort issues

  • Continuous insulation links around the entire envelope; gaps undermine performance

  • Airtightness (or draught-free construction) reduces uncontrolled air leakage, improving temperature stability, moisture control, indoor air quality, and acoustics

• Heat loss form factor (concept and example)

  • Heat loss form factor = surface area of the building envelope / usable floor area

  • In a dense, compact building (e.g., a flat in a block), the envelope to floor area ratio is much smaller, giving lower heat loss per unit floor area, hence better energy efficiency

  • Larger, more complex forms increase surface area and construction costs, often raising heat loss unless insulation and assemblies are improved

• Enclosing envelope: continuous insulation and barrier layers

  • The envelope must maintain warmth inside and dryness/structural integrity inside

  • Gaps or breaks in insulation create thermal bridges and moisture risks

• Airtightness and draught-free construction

  • Airtightness is essential for predictable performance and moisture control; it is not about eliminating all openings but about preventing uncontrolled air leakage

  • Passive House targets: very low leakage under pressure testing; in NZ, this is not yet a mandatory regulatory requirement but is central to the standard

  • In NZ context: typical existing NZ homes may show around $5 ext{ air changes per hour (ACH)}$ at 50 Pa; a blower door test assesses this

  • Passive House target (global standard) at 50 Pa: ext{ACH}_{50} = 0.6

  • German building code: 3 ACH if relying on windows for ventilation; 1.5 ACH if relying on mechanical ventilation (to avoid losing efficiency through leakage)

  • NZ and BRANZ note: advocacy for airtightness in new builds, but no mandatory test or standard yet

• Ventilation and heat recovery

  • Passive House uses balanced heat-recovery ventilation (HRV/ERV) with very quiet fans and high energy efficiency

  • Heat recovery efficiency often in the range of $ext{η}_{HR} \approx 75\% - 95\%$, sometimes higher in modern systems

  • Fresh air is continually supplied while stale air is exhausted with heat exchange, minimizing cross-contamination between intake and exhaust air

• Windows and doors (thermal performance in context)

  • Windows and doors are holes in the thermal envelope; even top-tier triple-glazed units have U-values around $U \approx 1.0$ (W/m²K), whereas well-insulated walls may achieve much lower heat transfer on average in the envelope

  • Window performance is crucial for heat gain in winter and heat loss in winter; condensation and frost behavior differ between inside vs outside surfaces depending on temperature and humidity

  • Climate-dependent glazing choices: NZ South Island often requires triple glazing for Passive House; North Island can often use double glazing in many cases, with triple glazing where climate demands

• Design process and energy modelling

  • PHPP (Passive House Planning Package) is the central planning tool for Passive House projects; designers also use SketchUp DesignPH for initial envelope modelling and shading analysis

  • EZPH: a lighter version of PHPP for smaller houses

  • The PH process acts as a “Swiss Army knife” for energy-efficient design: iterative design, checking heat gains/losses per room, and refining components (e.g., window sizes, shading, ventilation, insulation) during early design stages

• The heat balance concept (visual tool)

  • A monthly heat balance graph shows heat gains (from sun, occupants, appliances) versus heat losses (through walls, roof, floor, bridges, ventilation)

  • The balance guides where to focus design improvements (e.g., reducing heat loss through windows, improving ventilation efficiency)

What Passive House does not prescribe

• The standard does not dictate a specific architectural style, materials, or construction method

• It governs performance outcomes and requires verification of these outcomes through modelling and in-situ testing during construction and post-occupancy

• Retrofit/certification

  • Passive House includes a retrofit standard for refurbishments, enabling retrofit projects to achieve Passive House performance

  • There is also a Low Energy Standard (a separate NZ/PH-related standard with less stringent criteria) and component certifications (e.g., certified windows, ventilation systems)

  • Certifications can assess whole-building certification or retrofit projects, and there are also component-level certifications (windows, ventilation units, etc.)

• Roles in certification and training

  • Passive House designers can be certified through training and examinations; tradespeople can also be certified; certifiers provide independent verification of projects

  • Notable NZ players: Sustainable Engineering (certifier), Passive House Academy (training), and PH certification bodies

Energy modelling tools and verification during construction

• Energy modelling workflow in Passive House

  • Early design modelling with DesignPH (SketchUp plug-in) to model thermal envelope and shading

  • Detailed performance modelling with PHPP (Passive House Planning Package)

  • EZPH: a lighter version for small projects

  • The modelling yields a prediction of building performance and informs design decisions (e.g., optimal window sizes, shading, insulation levels, ventilation strategies)

• Heat balance chart (monthly) in PHPP

  • Sides: heat gains (sun, occupants, equipment) vs heat losses (walls, roof, floor, thermal bridging, ventilation)

  • Result: predicted heating demand and overall energy balance

  • Helps identify critical areas (e.g., windows and ventilation as major contributors to heat loss; influence where to improve performance)

• Construction verification and testing

  • Beyond design and modelling, Passive House requires verification during construction

  • Draught-free construction must be verified; ventilation must be commissioned to ensure proper fresh air delivery and safety

  • Construction observation adds focus on critical aspects impacting performance

  • Blow door testing (air tightness test) is common in many contexts but not currently mandated by NZ Building Code; nonetheless, professionals advocate for airtightness targets

  • Typical NZ homes: around $5 ext{ ach}$ at 50 Pa; Passive House target: $0.6 ext{ ach}$ at 50 Pa

  • By comparison, a leaky house (example from Kapiti) can show much higher ACH (e.g., 16 ACH) indicating poor performance without proper envelope integrity

Notable NZ and international project examples and contexts

• NZ projects discussed

  • Toi Ora Co-housing, Otago/Dunedin: 21 houses on a former school site, designed as a co-housing development

  • Kainga Ora project, Auckland: 18 social housing units; state-funded passive house project (noting changing political/financial contexts)

  • A NZ office project in Wanaka: first certified Passive House office in NZ and among early Passive House Plus offices globally (generates surplus energy)

  • Queenstown project: very thick wall insulation (nearly 300 mm) and roof insulation around 300 mm; showcases high insulation demands in extreme sun and alpine climates

  • Wellington Newlands project: wall assembly around 200 mm total insulation (140 mm stud + 50 mm insulation on inside), standard suburban-like construction with high performance

  • Palmerston North project: simpler wall assembly with ~150 mm total insulation (90 mm framing + 50 mm inner layer) with substantial roof insulation

• International and broader context

  • Cross Church (Christchurch) – a certified Passive House project

  • Roosevelt Island, New York – one of the earlier tall Passive House student residence blocks

  • Canada, Spain, China – examples of office buildings, social housing, and large-scale passive housing initiatives

• Materials and sustainability synergy

  • Passive House supports low-carbon and ecological design through strong envelope performance, potential for bio-based materials, mass timber, and reuse of materials

  • The Passive House approach often aligns with broader sustainable engineering and climate-related design goals

Certification, training, and resources

• Certification options

  • Whole-building Passive House certification (new builds and renovations)

  • Passive House Plus (buildings that generate energy on site)

  • Retrofit Passive House certification for refurbishments

  • Low Energy standard (NZ variant with lower requirements)

  • Component certifications (windows, ventilation systems, etc.)

• Training and credentials

  • Passive House Designer certification (via courses and exams or demonstrated through a certified project)

  • Passive House Tradesperson certification for builders

  • Passive House Certifier (independent verifier)

• Notable NZ providers and resources

  • Sustainable Engineering (certifier and NZ-based consulting firm)

  • Passive House Academy (training and webinars)

  • Passivhaus Institute (Germany) and the Passivhaus Encyclopedia

• Key reference materials and online resources

  • High Performance Construction Details Handbook (HPCD): a comprehensive reference with 100+ details and 83 junctions; includes energy modelling implications, condensation risks, embodied carbon, and cost considerations; available from the Passivhaus Institute NZ site (pasovase.nz) and BRANZ (ER70)

  • The “Passive House Home So People Thrive” brochure (from Passivhaus Institute materials)

  • Websites with ongoing project databases and technical articles: Sustainable Engineering (NZ), Passivhaus Institute (Germany), Passivhaus Encyclopedia, and an international database of Passivhaus projects

• Practical takeaway for students and practitioners

  • PHPP and DesignPH become essential tools in the Passive House workflow

  • Always treat the building as a system; improvements in one area (e.g., insulation) must be matched with improvements in other areas (ventilation, airtightness, glazing) to achieve overall performance

  • Energy modelling supports decision-making across design stages and provides quantitative insight into comfort and energy outcomes

Recap of key numerical references and concepts

• Global certification footprint

  • $4{,}500{,}000 ext{ m}^2$ of certified useable floor area worldwide (as of 2025)

• NZ certification and milestones

  • ~$165$ certified units (as of 2025); first NZ Passive House in 2012 (Auckland single-family home)

  • Notable NZ examples: Toi Ora co-housing (Otago/Dunedin, 21 houses); Kainga Ora 18-unit Auckland project (state-funded)

• Climate and glazing considerations

  • South Island NZ: often triple glazing needed for Passive House performance

  • North Island NZ: double glazing frequently acceptable, with triple glazing where climate requires

• Envelope and performance targets

  • Airtightness target: $ext{ACH}_{50} = 0.6$

  • German code with mechanical ventilation: $ext{ACH} ext{ (with ventilation)} = 1.5$; with windows only: 3 ACH

  • NZ context: typical new houses around 5 ACH (leaky by Passive House standards)

• Heat balance and energy outcomes

  • Passive House reduces heating requirements by about 90 ext{%} and overall energy use by roughly 50 ext{%} - 60 ext{%} depending on other energy uses

• Heating load example

  • A passive house around $200 ext{ m}^2$ can be heated adequately with approximately $2 ext{ kW}$ of heating power (comparable to a hairdryer) to maintain comfort year-round

• Fan and ventilation efficiency

  • HRV/ERV systems with high efficiency and low energy use; heat recovery efficiencies commonly in the range

Final notes and guidance for exam preparation

• Focus on understanding Passive House as a performance standard with predictable outcomes, not a design prescription

• Remember the five core design characteristics (envelope continuity, airtightness, ventilation with heat recovery, window/door performance, and energy modelling)

• Be able to explain the heat loss form factor and its implications for building form and cost

• Know the differences between climate-specific requirements and how glazing choices vary by NZ climate

• Understand the role of energy modelling tools (DesignPH, PHPP, EZPH) and how a heat balance graph informs design decisions

• Recognize the importance of construction verification, including airtightness testing and proper commissioning of ventilation systems

• Be familiar with the certification pathways, training opportunities, and key NZ players/resources

• Be prepared to discuss real-world project examples from NZ and internationally to illustrate how Passive House principles are applied in practice