Prepare for the CPHD by treating every Passive House criterion as a design decision with a verifiable chain behind it: a drawing decision changes an input, the input changes a result, and the result trades off against another criterion. Rehearse that chain with numbers on simplified buildings, drill thermal bridge and overheating scenarios, and finish with timed mixed practice. For registration, exam dates, and administrative details, refer to the Passive House Institute website at passivehouse.com.
Turning the Five Principles into Diagnostic Checks, Not Slogans
The classic Passive House principles — continuous thermal envelope, thermal bridge free detailing, airtightness, mechanical ventilation with heat recovery, and controlled solar gains — are most useful when studied as diagnostic checks: each has an input you change, an effect you predict, and a result you verify.
For each principle, write out its chain explicitly. Envelope continuity changes the area-weighted U-value and the external geometry entered in an energy balance; airtightness changes the leakage input that affects both heating demand and how much air actually passes through the recovery unit; glazing and shading change both winter gains and summer behavior. Rehearse the direction of change first, then the rough magnitude. Saying 'lower envelope U-values reduce heating demand, but returns diminish as the envelope improves' is exam-usable reasoning; reciting a definition is not.
Run a simple variation exercise on a one-room box building with assumed geometry. Predict what happens to annual heating demand when you halve window U-values, then when you improve airtightness from a leaky assumption to a high-quality target, then when you add a heat recovery unit. Before checking any tool, write your predicted ranking of the three effects. Expected observations: glazing and ventilation improvements usually dominate on a leaky, poorly glazed box; once those are fixed, further envelope improvement yields smaller reductions. If your ranking was wrong, trace which loss term you underestimated.
Why Heating Demand and Heating Load Answer Different Questions
Heating demand, in kWh per square metre of treated floor area per year, measures annual energy; heating load, in watts per square metre, measures peak power under design weather conditions. Sizing decisions depend on the load, while efficiency assessment depends on the demand.
The two numbers diverge because they integrate differently. Demand spreads heating need across the whole heating season, so a building meeting a commonly cited Passive House demand level around 15 kWh/(m²a) averages very low power over the year. Load asks a different question: on the coldest design day, at a defined design outdoor temperature, how much heat must the system deliver at once? This is why the Passive House approach treats roughly 10 W/m² as a reference scale for the heating load. A question that mentions 'design conditions' or 'system capacity' is a load question; one that mentions annual results is a demand question.
Worked scenario: a designer checks that a small house meets the annual demand criterion and specifies heating equipment based on that annual figure divided across operating hours. The mistake is confusing the two quantities: the equipment must cover the peak load, which occurs on the design day, not the seasonal average. The better decision is to compute the design-day heat load separately and size the system against that, then use the demand result for the energy assessment. Why it matters: an under-capacity system fails comfort on cold mornings even when the annual energy budget looks excellent, and the two fixes involve entirely different design levers.
Linear and Point Thermal Bridges: The Balcony Slab Decision
U-values describe area-based heat flow through plane elements; psi values describe linear thermal bridges along edges and junctions in W/(m·K); chi values describe point thermal bridges in W/K. Thermal bridges must be judged on both energy loss and interior surface temperature.
Keep the three transmittance types distinct in your notes. The U-value is a property of a building element; psi attaches to a junction, such as a wall-floor connection, a window reveal, or a balcony attachment; chi attaches to a penetrating point, such as an anchor. The energy consequence is that junctions add heat flow beyond what the plane U-values predict. The comfort and durability consequence is equally exam-relevant: a strong thermal bridge depresses the interior surface temperature at that junction, which is evaluated with the temperature factor, and a cold surface raises the risk of condensation and mould. Every thermal bridge decision should therefore have two checks, not one.
Worked scenario: a design uses a continuous reinforced concrete balcony slab projecting through the insulation layer. The plausible mistake is assessing only the slab's own U-value and concluding the wall is fine; in reality the junction creates a significant linear bridge, heat drains through the slab, and the interior corner surface temperature drops toward the condensation range. The better decision is to interrupt the bridge — a thermally broken balcony connection, or a structurally separate self-supporting balcony — and then account for the remaining junction psi in the energy balance. Why it matters: the flaw is invisible on the wall section itself and appears only at the junction, which is exactly where simplified analysis goes wrong.
| Transmittance type | What it describes | Units | Typical location | What it affects |
|---|---|---|---|---|
| U-value | Heat flow through a plane building element | W/(m²·K) | Walls, roofs, floors, glazing | Envelope heat loss total |
| psi (linear) | Extra heat flow along a junction edge | W/(m·K) | Wall-floor ties, window reveals, balcony connections | Energy balance plus surface temperature at the edge |
| chi (point) | Extra heat flow through a single point | W/K | Anchors, fasteners penetrating insulation | Local heat loss and surface effects |
Planning Airtightness and Heat Recovery Ventilation as One System
Airtightness limits uncontrolled leakage through the envelope; a mechanical ventilation system with heat recovery delivers the controlled air change and reuses heat from exhaust air. They are one system: the airtight layer decides that air enters the building through the unit, not through cracks.
Study the pair jointly rather than as separate chapters. The airtight boundary must enclose the heated volume and be buildable: continuous, joined at penetrations, and clear enough that the site crew can trace it on every section. The ventilation concept then assumes that boundary exists — supply air enters rooms through the unit, extract air leaves through it, and the recovery efficiency applies to air that actually passes through. If the envelope leaks, part of the air change bypasses the recovery process, so both the airtightness result and the effective recovery benefit degrade together. The classic verification pairing is the pressure test, expressed as air changes per hour at a set pressure difference, against the ventilation design.
Worked scenario: a design achieves an excellent airtightness target but locates no ductwork routes and provides no path for makeup or exhaust air beyond the unit. The plausible mistake is treating the pressure-test number as the deliverable and the ventilation concept as a later fit-out problem. The better decision is to fix both on the drawings together: trace the airtight line on each section, mark every penetration and its sealing detail, and route supply and extract paths for all habitable rooms before construction starts. Why it matters: an airtight boundary without a coherent ventilation concept creates an indoor-air problem, while a ventilation concept without a buildable boundary undercuts the recovery it depends on.
Winter Solar Gains Versus Summer Overheating on the Same Facade
Glazing that reduces winter heating demand by admitting solar gains can drive summer overheating on the same facade. Study gains as a two-sided decision: window area, orientation, glazing properties, and external shading must be weighed against an overheating check, not only the winter balance.
The physics pulls in opposite directions seasonally. In winter, solar gains through windows offset heating demand, so larger or better-transmitting glazing can improve the annual result. In summer, the same apertures admit heat that the building then must remove or buffer. The Passive House assessment therefore includes a summer comfort check — expressed in the energy balance tool as the share of hours of the year above 25 °C, typically held under a set limit — alongside the heating result. Learn to read the two results together: a design that improves demand while pushing the overheating share up has traded one criterion against another, and the honest answer is to adjust the design, not to celebrate the demand figure.
Worked scenario: to cut heating demand, a designer enlarges south-facing glazing and selects glazing with a high solar heat gain coefficient, then reports a strong winter result. The plausible mistake is stopping there; the better decision is to re-run the assessment with the summer comfort check, then optimize the ratio of window area to floor area, consider a lower solar transmittance where winter gains are not needed, and specify effective external shading such as operable shutters or blinds outside the glazing. Why it matters: internal-only shading intercepts heat that has already entered, and an overheating problem discovered late usually forces either mechanical cooling or a comfort penalty — both of which undermine the design's original goal.
Choosing Between New-Build Criteria and the EnerPHit Retrofit Route
EnerPHit is the Passive House standard for retrofit, applied where existing building conditions make full new-build criteria impractical. The designer's decision is which compliance route — component quality or an energy demand target — fits the building's fixed constraints.
Retrofit changes the decision structure because geometry, orientation, and construction are largely fixed. Existing thermal bridges, awkward shapes, or an orientation that cannot be improved may make new-build criteria unreachable at reasonable effort, which is the situation EnerPHit addresses with somewhat relaxed targets. Two routes exist in the retrofit standard: demonstrating the required quality of individual building components, or demonstrating a retrofit heating demand target. Learn what each route fixes and what it leaves free — the component route is component-by-component, while the demand route keeps attention on the whole-building energy balance with a retrofit-appropriate ceiling.
Worked scenario: a brick masonry dwelling has deep-plan extensions, party walls the owner cannot treat, and window positions that cannot change. The plausible mistake is forcing the design onto new-build criteria and either over-engineering a few components or abandoning certification entirely. The better decision is to assess the fixed constraints, identify which junctions and elements cannot realistically meet new-build quality, and evaluate the EnerPHit route — checking both which method fits and what the relaxed targets actually require. Why it matters: the retrofit standard exists precisely for this decision; a designer who cannot distinguish the routes will either undersell a feasible retrofit or promise performance the fabric cannot deliver.
A Study Sequence with a Self-Check Rubric and Readiness Criteria
Sequence preparation as: core concepts, energy-balance reasoning, detailing and thermal bridges, ventilation and airtightness as a pair, overheating and retrofit decisions, then timed mixed scenarios. Readiness means predicting results, naming the governing criterion, and stating the tradeoff without notes.
A practical six-block sequence: (1) the five principles as diagnostic chains; (2) demand versus load and how inputs flow through an energy balance; (3) thermal bridges — U, psi, chi, surface temperature, and detailing at junctions; (4) airtightness and ventilation planned jointly; (5) solar gains, shading, and the overheating check, plus the EnerPHit routes; (6) timed mixed practice using paper scenarios you write or adapt. Keep one notebook page per concept recording its input, effect, result, and tradeoff; that page becomes your revision sheet and forces the decision framing rather than definition recall.
Use this self-check rubric on each scenario you attempt, scoring 1–3 per row: criterion identification (can you name which Passive House criterion governs the decision?); quantitative reasoning (can you predict the direction and rough magnitude of the effect?); tradeoff articulation (can you state which other criterion is pushed in the opposite direction?); documentation logic (can you say what must be drawn, calculated, or tested to verify the decision?). A total of 10–12 across four rows on unfamiliar scenarios is a useful learning milestone before mixed timed practice. These scores measure study progress only; they are not a prediction of any exam outcome.
- Block 1–2: rewrite each principle as an input → effect → result → tradeoff chain; test it on a box-building variation exercise.
- Block 3: drill three junction details (balcony, window reveal, wall-floor tie) and classify each extra flow as U, psi, or chi.
- Block 4: on one section drawing, trace the airtight line and the supply/extract air routes in different colors; every penetration gets a sealing note.
- Block 5: run one winter-optimization scenario, then re-check it against the summer comfort result and adjust shading or glazing.
- Block 6: complete timed mixed scenarios; apply the four-row rubric and revisit any block scoring below 2.
- Readiness checks: you can state demand vs load without notes, identify a thermal bridge from a junction sketch, explain why airtightness and ventilation are one system, and name both EnerPHit compliance routes.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.