Existing Building Performance Guide
A Passive House retrofit applies the principles, modelling and quality-assurance methods of the Passive House framework to an existing building. Where formal retrofit certification is pursued, the relevant standard is commonly EnerPHit.
Existing homes present conditions that do not arise in the same way on new buildings. Orientation, structural junctions, floor levels, roof geometry, boundaries, heritage fabric and concealed construction may already be fixed before the retrofit begins.
EnerPHit accounts for these constraints while retaining a defined pathway for energy demand, envelope performance, airtightness, ventilation, documentation and construction verification. It should not be used as a general label for any renovation that adds insulation or improves windows.
This guide focuses specifically on the retrofit pathway. For the wider standard, five principles, Australian climate application and PHPP framework, see the Passive House in Australia Knowledge Hub.
In Brief
Passive House Retrofit
A general description for applying Passive House principles, assessment and detailing to an existing building.
EnerPHit
The established Passive House Institute standard for qualifying energy-efficient retrofits of existing buildings.
Certification Boundary
Using selected principles does not make a project EnerPHit certified. Certification requires the applicable independent review and project evidence.
Some existing buildings may be capable of achieving the full Passive House standard. EnerPHit provides a separate retrofit pathway where existing structural and architectural conditions make the new-building criteria difficult to achieve.
Retrofit Standard
EnerPHit is the Passive House Institute standard developed for the energy-efficient retrofit of existing buildings using Passive House components and principles. It recognises that existing conditions may prevent every part of a building from being resolved in the same way as a new project.
A retained slab edge, adjoining wall, heritage façade, existing basement, fixed roof form or restricted boundary may create thermal and construction constraints that cannot reasonably be removed. EnerPHit accommodates the realities of retrofit while retaining defined comfort, energy, airtightness and quality-assurance requirements.
The standard is not a reduced-detail version of Passive House. A retrofit still requires coordinated modelling, envelope design, moisture-aware construction, ventilation planning, documentation and verification appropriate to the selected pathway.
Exact criteria vary by climate and certification method and should be confirmed against the current requirements applying to the individual project.
Pathway Boundaries
Applying Passive House principles. The renovation uses selected envelope, airtightness, window or ventilation strategies without claiming formal assessment or certification.
PHPP-informed retrofit design. The proposed works are modelled and refined using PHPP, but the project does not necessarily complete independent certification.
Formal EnerPHit or Passive House certification. The model, drawings, construction information, testing and applicable evidence are independently reviewed against the relevant building criteria.
Existing-Building Constraints
A new building can establish its form, orientation, envelope geometry, structural junctions and services routes around the intended performance standard. A retrofit begins with a building in which many of those decisions have already been made.
Existing construction may also be uncertain. Original drawings may be incomplete, insulation may be concealed, wall cavities may vary and past additions may use different construction systems. The design team may need investigation, measured information and carefully recorded assumptions before modelling can be relied upon.
Retrofit design must therefore coordinate energy performance with retained fabric, weatherproofing, moisture behaviour, structure, planning controls, heritage requirements, buildability and the intended construction sequence.
Certification Methods
Whole-Building Outcome
The retrofit is assessed against the applicable whole-building energy-demand criteria using the project’s PHPP energy balance and supporting information.
Component Performance
The project demonstrates that relevant building components satisfy the applicable climate-specific EnerPHit requirements, together with the wider certification criteria.
The appropriate method should be determined for the individual building and agreed with the appointed certifier. The two methods should not be simplified into a universal product schedule or generic retrofit specification.
Staged Renovation
Yes. Some owners replace building components progressively rather than completing the entire retrofit in one construction programme. A staged approach may align works with maintenance cycles, occupancy, funding or planned alterations.
Individual measures should still form part of an overall building strategy. Replacing windows without planning their future insulation and airtightness junctions, for example, may create difficult interfaces when the walls are upgraded later.
The EnerPHit Retrofit Plan records the intended sequence and completed condition so that separate stages can work toward a coherent final outcome. Pre-certification may also be available where the applicable requirements have been satisfied.
A staged plan does not mean that every isolated upgrade is automatically certified. The project must still follow the relevant planning, evidence and certification process.
Technical Coordination
Existing Fabric
Existing wall, floor and roof systems need to be understood before insulation values, airtightness details or moisture behaviour can be assessed reliably.
Insulation Strategy
Insulation location affects internal floor area, façades, eaves, junctions, moisture conditions, weatherproofing and the continuity of the thermal layer.
Air Control
The airtight layer must be traceable across retained and new construction, including floors, roofs, internal junctions, openings and service penetrations.
Openings
Window performance depends on glazing, frames, installation position, perimeter insulation, airtight sealing, shading and the retained surrounding fabric.
Junctions
Retained slabs, masonry walls, balconies, roof connections and structural elements may create fixed thermal bridges requiring project-specific review.
Building Services
Ventilation equipment, duct routes, intake and exhaust locations, heating and cooling systems and service penetrations must fit within the retained building.
Moisture and Existing Fabric
Adding insulation and reducing air leakage changes how heat and moisture move through existing building elements. Materials that previously dried in one direction may behave differently after an internal lining, external insulation layer, membrane or new cladding system is introduced.
Airtightness should not be confused with making an assembly unable to dry. Air-control, vapour-control, weatherproofing and ventilation perform different functions and must be coordinated for the construction type and climate.
Some retrofit junctions or assemblies may require specialist condensation or hygrothermal analysis. PHPP provides the building energy balance, but it should not be treated as a replacement for every detailed moisture assessment that a project may need.
Existing leaks, rising damp, drainage defects and material deterioration should be understood and addressed rather than concealed within a new high-performance envelope.
Heritage and Retained Character
Potentially. Heritage and character buildings can be considered, but retained façades, windows, roof forms, chimneys, decorative features and planning controls may limit where new performance layers can be placed.
External insulation may not be acceptable on a protected façade. Internal insulation may preserve external character but introduce different floor-area, junction and moisture considerations. Original windows may need to be retained, repaired, supplemented or assessed within the broader design strategy.
The performance target, planning obligations, conservation objectives and building-physics response should therefore be developed together. EnerPHit does not remove heritage or approval requirements applying to the property.
Existing-Building Information
Existing Building
Measured plans, elevations, sections, orientation, photographs, condition information and any available original documentation.
Construction
Known wall, floor and roof build-ups, retained materials, insulation, windows, past alterations and investigation findings.
Proposed Works
Alteration drawings, new envelope systems, window schedules, junction details, shading and the proposed airtightness strategy.
Services
Existing and proposed ventilation, heating, cooling, hot-water systems, plant locations, duct routes and service penetrations.
Project Constraints
Heritage controls, planning conditions, boundaries, retained rooms, occupancy needs, programme, access and construction staging.
Intended Pathway
Whether the project is applying principles, using PHPP, targeting EnerPHit, considering full Passive House or planning a staged retrofit.
Project Pathway
Stage 01
Confirm the intended performance or certification objective and assemble the available information about the existing building.
Stage 02
Review the retained construction, constraints, moisture conditions and likely envelope and services opportunities.
Stage 03
Where commissioned, model the existing and proposed building and test the developing retrofit strategy under the relevant methodology.
Stage 04
Develop insulation, airtightness, windows, thermal bridges, moisture control, ventilation and services details with the wider consultant team.
Stage 05
Deliver the documented retrofit, record relevant construction information and complete testing or commissioning through the appointed specialists.
Stage 06
Where pursued, the appointed certifier reviews the final model, documents, test results and applicable project evidence before determining the outcome.
Existing-Home Assessment Boundary
No. A Home Energy Rating assesses how an existing Australian dwelling performs and may help identify practical upgrade opportunities. It belongs to the emerging existing-homes rating and improvement pathway.
EnerPHit is a separate international deep-retrofit standard. It requires PHPP assessment, coordinated envelope and services design, defined project evidence and independent certification where the formal pathway is pursued.
A homeowner who wants to understand the present performance of an existing dwelling may not need an EnerPHit project. A building already entering a substantial, technically coordinated retrofit may require a different level of assessment and documentation.
For the broader assessment of an existing dwelling and potential improvement pathway, see Home Energy Ratings for Existing Homes.
Cost and Programme
There is no universal EnerPHit construction premium, consultant fee, programme or payback period. Retrofit scope depends heavily on the building’s condition, accessibility, retained elements, project location and intended certification pathway.
Existing Condition
Unknown construction, defects, hazardous materials, deterioration and incomplete records can affect investigation and delivery.
Retrofit Depth
A whole-building deep retrofit differs substantially from targeted principles or staged component replacement.
Design Complexity
Heritage fabric, difficult junctions, internal insulation and limited plant or duct space can increase coordination requirements.
Certification Scope
Modelling, specialist analysis, testing, commissioning, construction evidence and independent review remain distinct workstreams.
A reliable scope requires review of the actual building and proposed works. Generic percentage savings or fixed retrofit costs should not be treated as a project forecast.
Common Misunderstandings
EnerPHit is not the name for every energy-efficient renovation. It is a defined certification standard.
Adding insulation does not establish EnerPHit performance. The complete building and applicable evidence must be considered.
Airtightness does not mean eliminating ventilation. Planned ventilation becomes more important as uncontrolled air leakage is reduced.
PHPP does not replace detailed moisture analysis. Some assemblies may require separate specialist review.
A Home Energy Rating is not EnerPHit certification. The systems have different purposes and assessment pathways.
Using the principles is not formal certification. Only the completed independent process establishes the certified outcome.
Frequently Asked Questions
It is the application of Passive House principles, modelling and quality-assurance methods to an existing building. The project may use selected principles, undertake PHPP-informed design or pursue formal EnerPHit or Passive House certification.
What is EnerPHit?EnerPHit is the Passive House Institute standard for qualifying energy-efficient retrofits of existing buildings. It recognises constraints that may make the full new-building Passive House criteria difficult to achieve.
Can an existing home achieve full Passive House certification?Potentially. The appropriate pathway depends on the existing building, proposed works and applicable criteria. EnerPHit is available where retained conditions make the full Passive House standard difficult to achieve.
Can EnerPHit work for a heritage home?It may be possible, but heritage fabric and planning controls can affect insulation location, windows, airtightness details and retained junctions. The conservation and performance strategies need to be coordinated for the individual property.
Does every window need to be replaced?Not as a universal rule. Window decisions depend on the existing units, heritage constraints, climate, energy balance, installation details and intended certification method. Retention, repair, secondary glazing or replacement may need project-specific assessment.
Can a Passive House retrofit be completed in stages?Yes. A staged approach can be planned through an EnerPHit Retrofit Plan so that separate measures work toward a coordinated final outcome rather than creating incompatible junctions or replacement decisions.
Is mechanical ventilation required?Controlled mechanical ventilation forms part of the Passive House framework. The proposed system must be coordinated with the building, climate, airtightness strategy and applicable certification requirements.
Is EnerPHit the same as a Home Energy Rating?No. A Home Energy Rating describes the existing performance of an Australian dwelling and may support practical upgrade decisions. EnerPHit is a separate deep-retrofit and certification standard using PHPP and defined project evidence.
Who certifies an EnerPHit project?Formal certification is completed by an appropriately accredited Passive House Building Certifier. The certifier independently reviews the PHPP model, technical documentation, testing and applicable construction evidence.
When should retrofit planning begin?Planning should begin before windows, insulation systems, façades, roofs and services are fixed. Early coordination preserves more options and helps avoid measures that conflict with later retrofit stages.
Related Guidance
Existing Building Review
Send the available existing and proposed drawings, photographs, known construction information and project objectives for an initial scope review. Certified Energy can help clarify whether PHPP-informed retrofit design, EnerPHit planning or another existing-home assessment pathway may be relevant. Independent certification remains a separate appointed role.
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