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Certified Passive House Designer / Consultant study materials
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Certified Passive House Designer / Consultant practice questions

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Question 1Passive House principles, certification criteria and the PHPP

Under the Passive House certification criteria, what is the maximum annual space heating demand?

  1. 50 kWh/m² of treated floor area per year
  2. 120 kWh/m² of treated floor area per year
  3. 15 kWh/m² of treated floor area per year Correct answer.
  4. 25 kWh/m² of treated floor area per year

Explanation

The classic Passive House heating criterion limits useful space heating demand to 15 kWh/m² TFA per year, or alternatively a peak heating load of 10 W/m². This very low figure is what distinguishes Passive House from low-energy standards that allow two to eight times more.

Question 2Passive House principles, certification criteria and the PHPP

Which metric does the Passive House primary energy criterion limit?

  1. Heating energy only, excluding domestic hot water
  2. Site electricity consumption only
  3. Total primary energy demand for all energy services, renewable and non-renewable Correct answer.
  4. Embodied carbon of the building envelope

Explanation

The primary energy criterion caps total primary energy demand from all energy uses, including heating, hot water, ventilation, lighting and appliances, converted using source-energy factors. It exists to prevent a building from meeting the heat limit while wasting large amounts of energy elsewhere.

Question 3Passive House principles, certification criteria and the PHPP

The Passive House airtightness criterion is expressed as which maximum value?

  1. n50 = 0.6 air changes per hour at 50 Pa Correct answer.
  2. n50 = 0.1 air changes per hour at 50 Pa
  3. n50 = 1.0 air change per hour at 50 Pa
  4. n50 = 3.0 air changes per hour at 50 Pa

Explanation

Certification requires a pressurisation test result of no more than 0.6 air changes per hour at a 50 Pa pressure difference. This tight envelope keeps infiltration losses small and protects the insulation and structure from moisture-laden air movement.

Question 4Passive House principles, certification criteria and the PHPP

What is the maximum permitted frequency of indoor air temperatures above 25 °C during the summer period in a certified Passive House?

  1. No more than 50 % of the hours
  2. No more than 10 % of the hours Correct answer.
  3. No more than 25 % of the hours
  4. No limit is set as long as cooling energy is low

Explanation

The summer comfort criterion allows overheating above 25 °C for at most 10 % of the hours in the cooling-relevant period. This ensures passive measures such as shading and night ventilation keep occupants comfortable without relying on active cooling.

Question 5Passive House principles, certification criteria and the PHPP

What does the treated floor area (TFA) used in Passive House metrics represent?

  1. The net usable floor area inside the thermal envelope, measured to defined rules Correct answer.
  2. The total site area including terraces and gardens
  3. Only the heated living rooms, excluding circulation
  4. The gross external footprint of the building

Explanation

TFA is the usable floor area within the thermal envelope, calculated with standardised rules that exclude some zones and apply factors to others. All demand and load indicators are normalised by TFA so that buildings of different size can be compared fairly.

Question 6Passive House principles, certification criteria and the PHPP

In PHPP, what is the purpose of the verification page?

  1. It generates the bill of quantities for construction
  2. It stores the climate data used for the calculation
  3. It summarises the key results and compares them with the certification criteria Correct answer.
  4. It calculates the U-values of individual building components

Explanation

The verification sheet collects the headline results such as heating demand, primary energy and overheating frequency and sets them against the Passive House limits. It is the page a certifier reviews first to judge whether the building passes.

Question 7Passive House principles, certification criteria and the PHPP

Which heat-recovery efficiency must a ventilation unit typically achieve to support the Passive House energy balance?

  1. Exactly 100 %
  2. At least 50 %
  3. At least 30 %
  4. At least 75 % Correct answer.

Explanation

Passive House ventilation units are expected to reach a certified heat-recovery efficiency of at least 75 %, with low fan power and frost protection. High recovery keeps ventilation heat losses small, which matters because a tight envelope makes ventilation the dominant air-related loss.

Question 8Passive House principles, certification criteria and the PHPP

What is the Passive House peak heating load criterion?

  1. No load criterion exists, only annual demand
  2. 25 W/m² of treated floor area
  3. 40 W/m² of treated floor area
  4. 10 W/m² of treated floor area Correct answer.

Explanation

The heating criterion can be met either through the annual demand of 15 kWh/m² or through a peak load of 10 W/m² TFA. The load limit is what allows the building to be heated by the supply air of the ventilation system alone.

Question 9Passive House principles, certification criteria and the PHPP

A designer wants to reduce the transmission heat loss of a wall assembly in PHPP. Which change has the most direct effect on the calculated loss?

  1. Increasing the window-to-wall ratio on that facade
  2. Raising the indoor set-point temperature
  3. Increasing the thermal conductivity of the insulation layer
  4. Lowering the U-value by adding insulation thickness Correct answer.

Explanation

Transmission loss is the product of U-value, area and temperature difference, so lowering the U-value through added insulation directly reduces it. The other changes either worsen the loss or alter boundary conditions rather than the assembly performance.

Question 10Passive House principles, certification criteria and the PHPP

Why does PHPP require the thermal-bridge surcharge to be entered explicitly rather than ignored?

  1. Because thermal bridges only affect cooling demand
  2. Because it is only relevant for steel-framed buildings
  3. Because unaccounted junctions can add significant heat loss and risk condensation Correct answer.
  4. Because the surcharge replaces the need for airtightness testing

Explanation

Junctions such as balconies, window reveals and floor slabs create additional heat flow that is not captured by the planar U-values. PHPP applies a thermal-bridge surcharge or detailed psi-values so that the energy balance and moisture assessment remain realistic.

Question 11Passive House principles, certification criteria and the PHPP

In the PHPP heating balance, what does the useful solar gains term account for?

  1. Solar radiation transmitted through glazing and absorbed in the space Correct answer.
  2. Heat recovered by the ventilation unit
  3. Solar radiation absorbed by opaque walls and roofs only
  4. Heat emitted by internal light fittings

Explanation

Useful solar gains are the portion of transmitted radiation through windows that contributes to heating the space, reduced by shading and frame effects. Opaque absorption is handled through the sol-air effect and is far smaller than window gains.

Question 12Passive House principles, certification criteria and the PHPP

A project shows a heating demand of 14 kWh/m² but a primary energy demand of 130 kWh/m². What is the most likely explanation?

  1. The airtightness test has not been carried out
  2. The building uses high primary-energy-factor energy for appliances, hot water or auxiliary electricity Correct answer.
  3. The treated floor area was entered incorrectly
  4. The envelope is too poorly insulated

Explanation

The heating criterion is met while the primary energy criterion fails, which points to energy uses other than heating or to a high source-energy factor. Appliances, domestic hot water and auxiliary electricity are common causes of an elevated primary energy figure.

Question 13Passive House principles, certification criteria and the PHPP

How does PHPP treat the effect of window shading devices in the summer calculation?

  1. It ignores shading and assumes fully clear glazing
  2. It applies a shading reduction factor to the solar gains Correct answer.
  3. It increases the internal gains to compensate
  4. It lowers the ventilation rate automatically

Explanation

External shading, reveals and orientation are captured through reduction factors applied to the incident solar radiation. This is why well-designed shading can keep overheating below the 10 % limit without mechanical cooling.

Question 14Passive House principles, certification criteria and the PHPP

What is the role of the specific heat capacity and effective area of thermal mass in the PHPP summer calculation?

  1. They set the airtightness requirement
  2. They dampen temperature swings by storing and releasing heat, affecting overheating frequency Correct answer.
  3. They replace the need for shading
  4. They determine the heating load in winter only

Explanation

Thermal mass absorbs heat during the day and releases it later, reducing peak temperatures and the number of hours above 25 °C. PHPP uses the effective storage mass and its area to model this dynamic behaviour.

Question 15Passive House principles, certification criteria and the PHPP

Which statement correctly describes the Passive House renewable energy criterion (PER)?

  1. It requires all heating to be electric
  2. It counts only on-site photovoltaic generation
  3. It limits primary energy demand from non-renewable sources, allowing renewable generation to offset demand Correct answer.
  4. It replaces the airtightness requirement

Explanation

The PER criterion limits the primary energy demand from non-renewable sources and allows on-site or nearby renewable generation to be credited against that demand. It encourages efficient buildings to combine low demand with renewable supply.

Question 16Passive House principles, certification criteria and the PHPP

A designer is choosing between a balanced ventilation system with heat recovery and simple extract ventilation for a Passive House. Why is the balanced system preferred?

  1. It recovers heat from exhaust air and supplies filtered fresh air without draughts Correct answer.
  2. It removes the need for an airtight envelope
  3. It avoids the need for any insulation
  4. It allows higher infiltration losses to be tolerated

Explanation

A balanced system with heat recovery supplies fresh filtered air while recovering heat from the exhaust, keeping ventilation losses low. It also provides controlled, draught-free supply, which is essential in a very tight envelope.

Question 17Passive House principles, certification criteria and the PHPP

How is domestic hot water demand typically reduced in a Passive House design?

  1. By removing hot water entirely from the calculation
  2. By using drain-water heat recovery and efficient distribution with short pipe runs Correct answer.
  3. By relying on solar gains through windows
  4. By increasing the storage tank temperature to 90 °C

Explanation

Drain-water heat recovery, compact distribution and well-insulated storage reduce the energy needed for hot water. Short pipe runs also cut distribution losses, which can be significant in low-demand buildings.

Question 18Passive House principles, certification criteria and the PHPP

What does the PHPP internal heat gain input represent?

  1. Solar radiation absorbed by internal surfaces
  2. Heat from occupants, lighting and appliances per unit of treated floor area Correct answer.
  3. Heat lost through the ventilation system
  4. Heat generated by the heating system

Explanation

Internal gains are the heat released by people, lighting and equipment, usually entered as a specific value per square metre of TFA. They reduce net heating demand in winter but contribute to overheating in summer.

Question 19Passive House principles, certification criteria and the PHPP

A building meets the heating demand criterion but its measured airtightness is 1.2 h⁻¹ at 50 Pa. What is the correct conclusion?

  1. It passes because the heating demand already complies
  2. It fails the airtightness criterion and must be improved before certification Correct answer.
  3. It can still be certified because airtightness is optional
  4. It can be certified if the primary energy demand is low

Explanation

Airtightness is a mandatory criterion independent of the energy results, so a result of 1.2 h⁻¹ exceeds the 0.6 h⁻¹ limit. The envelope must be sealed and retested before certification can be granted.

Question 20Passive House principles, certification criteria and the PHPP

Why does PHPP use a utilisation factor when crediting internal and solar gains?

  1. Because gains are always fully useful in winter
  2. Because gains are only partly useful and can cause overheating if fully credited Correct answer.
  3. Because it converts electricity into primary energy
  4. Because it accounts for the airtightness test

Explanation

Not all gains reduce heating demand, since some occur when the building is already warm or lead to overheating. The utilisation factor adjusts the credited gains so the calculated demand reflects reality rather than an optimistic full credit.

Question 21Passive House principles, certification criteria and the PHPP

A project team proposes meeting the heating criterion with a heat pump and underfloor heating but a poorly insulated envelope. Why does this approach conflict with Passive House principles?

  1. Because heat pumps are not permitted in Passive House
  2. Because the standard prioritises demand reduction through the envelope before efficient supply Correct answer.
  3. Because underfloor heating cannot be modelled in PHPP
  4. Because the primary energy criterion ignores heating

Explanation

Passive House follows the principle that avoided demand is cheaper and more robust than efficient supply, so the envelope must first bring the load down to about 10 W/m². A good heat pump on a leaky envelope cannot compensate for high transmission losses.

Question 22Passive House principles, certification criteria and the PHPP

Two designs have identical heating demand, but design A has a higher peak load because of larger glazed areas with poor frames. Which consequence is most relevant for certification?

  1. Design A will need no ventilation system
  2. Design A will have lower overheating risk
  3. Design A may fail the 10 W/m² load criterion and require a larger heating system Correct answer.
  4. Design A will automatically pass because annual demand is equal

Explanation

The load criterion is assessed separately from annual demand, so a design with a high peak load can fail even when annual demand complies. A higher load also means the supply-air heating strategy may no longer be sufficient.

Question 23Passive House principles, certification criteria and the PHPP

In a PHPP analysis, a designer reduces the ventilation air change rate to lower heating demand but keeps the same occupancy. What is the main risk of this change?

  1. The airtightness result will improve artificially
  2. The thermal-bridge surcharge will be double-counted
  3. The primary energy factor will increase
  4. Indoor air quality may deteriorate because fresh-air supply per person falls below acceptable levels Correct answer.

Explanation

Ventilation rates must satisfy indoor air quality and moisture removal for the actual occupancy, so cutting airflow purely to save energy can degrade air quality. PHPP inputs should reflect a rate that meets comfort and hygiene requirements, not an artificially low figure.

Question 24Passive House principles, certification criteria and the PHPP

Why can a very low U-value wall still underperform if the junction details are poor?

  1. Because poor junctions improve airtightness
  2. Because junctions can create local heat loss and cold surfaces that dominate the assembly performance Correct answer.
  3. Because junctions only affect the cooling load
  4. Because U-values are irrelevant in PHPP

Explanation

Repeating thermal bridges at slab edges, balconies and reveals can add substantial loss and lower internal surface temperatures, risking mould. This is why junction psi-values or a conservative surcharge must be included alongside the planar U-values.

Question 25Passive House principles, certification criteria and the PHPP

A consultant compares two glazing options: option 1 has a lower U-value but a lower solar transmittance, option 2 the reverse. On a cold, sunny south facade, what does PHPP likely show?

  1. Option 2 always fails the summer comfort criterion
  2. Option 2 may give lower heating demand because useful solar gains outweigh the higher transmission loss Correct answer.
  3. Both options give identical results because glazing is treated as opaque
  4. Option 1 always gives lower heating demand because U-value dominates

Explanation

On sunny south facades the net balance depends on both the U-value and the solar gains, and high transmittance can offset a slightly worse U-value. PHPP evaluates this balance monthly, so the better option depends on orientation and climate rather than U-value alone.

Question 26Passive House principles, certification criteria and the PHPP

Which airtightness requirement must a building meet to be certified as a Passive House?

  1. A maximum of 3.0 air changes per hour at 50 Pa pressure difference
  2. A maximum of 1.0 air changes per hour at 50 Pa pressure difference
  3. A maximum of 0.3 air changes per hour at 50 Pa pressure difference
  4. A maximum of 0.6 air changes per hour at 50 Pa pressure difference Correct answer.

Explanation

The Passive House standard sets a stringent airtightness limit of 0.6 air changes per hour at a pressure difference of 50 Pa (n50 ≤ 0.6 h⁻¹), verified by a blower door test. This limit is one of the three core certification criteria alongside heating demand and primary energy demand.

Question 27Passive House principles, certification criteria and the PHPP

What is the maximum space heating demand allowed for a building to be certified as a Passive House?

  1. 10 kWh/m² per year
  2. 15 kWh/m² per year Correct answer.
  3. 30 kWh/m² per year
  4. 50 kWh/m² per year

Explanation

The Passive House certification requires that the annual space heating demand does not exceed 15 kWh/m² of treated floor area per year. This limit is based on the energy needed for heating and is a key metric in the PHPP verification.

Question 28Passive House principles, certification criteria and the PHPP

In PHPP, how is the specific heat capacity of the building fabric accounted for in the summer ventilation concept?

  1. It is entered as a fixed value of 60 Wh/K per m² of treated floor area for all buildings.
  2. It is converted into an equivalent U-value and added to the transmission heat loss.
  3. It is used to calculate the effective thermal mass that buffers internal temperature swings and reduces overheating risk. Correct answer.
  4. It is ignored because summer comfort is assessed only by the peak internal temperature.

Explanation

PHPP uses the specific heat capacity of construction materials together with the effective area of thermal mass to determine how much heat can be stored and released, which dampens temperature swings and lowers the risk of overheating. This effective thermal mass is a key input in the summer ventilation worksheet.

Question 29Passive House principles, certification criteria and the PHPP

A designer is using PHPP to evaluate a window upgrade. The current glazing has a U-value of 0.80 W/(m²K) and a solar heat gain coefficient (SHGC) of 0.50. A new glazing option has a U-value of 0.60 W/(m²K) and a SHGC of 0.40. In a heating-dominated climate, what is the most likely effect on the annual heating demand?

  1. The heating demand will increase because the lower SHGC reduces useful solar gains more than the U-value improvement saves. Correct answer.
  2. The heating demand will decrease because the lower U-value reduces transmission losses, and the lower SHGC has no effect.
  3. The heating demand will remain unchanged because the two effects cancel each other out.
  4. The heating demand will decrease because both the U-value and SHGC are lower, reducing all heat flows.

Explanation

In a heating-dominated climate, useful solar gains through windows significantly reduce heating demand. A drop in SHGC from 0.50 to 0.40 reduces these gains, and the improvement in U-value from 0.80 to 0.60 W/(m²K) may not compensate, leading to a net increase in heating demand. PHPP would quantify this balance.

Question 30Passive House principles, certification criteria and the PHPP

In the PHPP, which input is used to determine the effective collector area for a solar thermal system in the domestic hot water balance?

  1. The aperture area of the collectors Correct answer.
  2. The roof area available for collector installation
  3. The absorber area of the collectors
  4. The gross area of the collector array

Explanation

PHPP uses the aperture area of the solar collectors, which is the transparent opening through which solar radiation enters, as the basis for calculating useful solar yield. This area best represents the actual solar energy captured and is distinct from the gross or absorber area.

Question 31Building envelope: thermal insulation, thermal bridges, airtightness and construction details

In the Passive House verification methodology, what does the specific transmission heat loss coefficient (often written as the heat-loss-relevant envelope area calculation) fundamentally describe?

  1. The total solar gains admitted through glazing during the heating period
  2. The volume of air exchanged through the ventilation system per hour at a reference pressure difference
  3. The heat flow through the opaque and transparent envelope per kelvin of temperature difference, normalised by the treated floor area Correct answer.
  4. The internal heat gains from occupants and appliances per unit of living area

Explanation

The transmission heat loss coefficient expresses how much heat escapes through the building envelope for each kelvin of indoor-outdoor temperature difference, and it is divided by the treated floor area so buildings of different sizes can be compared against the Passive House limit. It covers both opaque and transparent envelope elements.

Question 32Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A designer is selecting insulation for a Passive House wall in a climate with cold winters. Which material property most directly governs the thickness needed to reach a target U-value?

  1. The compressive strength class of the insulation board
  2. The water vapour diffusion resistance factor of the insulation
  3. The declared thermal conductivity lambda of the insulation Correct answer.
  4. The fire reaction class of the insulation

Explanation

U-value depends primarily on the thermal conductivity lambda and the layer thickness, so the thickness required to hit a target U-value is set by the declared lambda value. Other properties such as strength, diffusion resistance and fire class matter for detailing and compliance but do not set the insulation thickness for a given U-value.

Question 33Building envelope: thermal insulation, thermal bridges, airtightness and construction details

What is the purpose of the airtightness layer in a Passive House envelope?

  1. To prevent uncontrolled air movement through the construction, which would otherwise bypass the insulation and carry moisture Correct answer.
  2. To act as the vapour-open capillary break between the wall and the ground
  3. To provide the primary rain screen on the external face of the wall
  4. To increase the thermal resistance of the wall cavity by trapping still air

Explanation

The airtightness layer stops uncontrolled air leakage through gaps and joints. Leaking air bypasses the insulation and can carry warm moist air into cold parts of the construction, so airtightness protects both energy performance and durability.

Question 34Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Why does the Passive House standard place strong emphasis on minimising thermal bridges?

  1. Thermal bridges create localised heat loss and cold surface temperatures that can drive surface condensation and mould Correct answer.
  2. Thermal bridges reduce the sound insulation of the separating floors
  3. Thermal bridges raise the compressive strength of the insulation layer
  4. Thermal bridges increase the solar heat gain coefficient of glazing

Explanation

A thermal bridge is a path of higher heat flow through the envelope, producing extra heat loss and locally colder internal surfaces. Those cold surfaces raise the risk of surface condensation and mould, which is why junctions are designed and calculated carefully.

Question 35Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Which quantity is used to describe the severity of a point thermal bridge such as a penetrating fixing or a balcony connector?

  1. A point thermal transmittance, usually written as chi Correct answer.
  2. A linear thermal transmittance, usually written as psi
  3. A thermal conductivity, usually written as lambda
  4. A surface resistance, usually written as Rsi

Explanation

Point thermal bridges are quantified by a point thermal transmittance, typically the Greek letter chi, expressed in watts per kelvin. Linear thermal bridges along junctions use psi, and the two are handled separately in the heat-loss calculation.

Question 36Building envelope: thermal insulation, thermal bridges, airtightness and construction details

In a Passive House, which of the following is the typical design target for the building envelope airtightness, expressed as n50?

  1. 3.0 air changes per hour at 50 pascals
  2. 0.6 air changes per hour at 50 pascals Correct answer.
  3. 1.5 air changes per hour at 50 pascals
  4. 6.0 air changes per hour at 50 pascals

Explanation

The Passive House airtightness requirement is commonly stated as no more than 0.6 air changes per hour at a pressure difference of 50 pascals, verified by a blower door test. This is far tighter than typical conventional construction.

Question 37Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Why is a windtight layer placed on the cold side of the insulation in a timber-frame Passive House wall?

  1. To act as the internal vapour control layer
  2. To seal the wall so completely that no vapour can escape
  3. To stop external air movement through the insulation while allowing water vapour to diffuse outwards Correct answer.
  4. To provide the main structural bracing for the frame

Explanation

The windtight layer, usually a vapour-open membrane on the cold side, prevents outside air from washing through and cooling the insulation. Being vapour-open, it still allows moisture to diffuse outwards so the construction can dry.

Question 38Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A continuous layer of insulation is installed on the outside of a masonry wall in a Passive House retrofit. What is the main thermal advantage of this external position?

  1. It removes the need for any internal airtightness layer
  2. It increases the solar absorptance of the wall surface
  3. It allows the masonry to dry only towards the interior
  4. It keeps the masonry warmer and largely eliminates repeating thermal bridges at floor and wall junctions Correct answer.

Explanation

Placing insulation outboard keeps the structural masonry within the warm zone, raising internal surface temperatures and reducing repeating bridges where floors and partitions meet the wall. It also improves the drying behaviour of the masonry.

Question 39Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A designer must calculate the linear thermal transmittance of a wall-to-floor junction. Which approach is consistent with Passive House practice?

  1. Assume psi equals zero for all junctions in masonry construction
  2. Multiply the wall U-value by the junction length
  3. Use a two- or three-dimensional heat-flow model of the junction and derive psi from the difference against the unbridged reference case Correct answer.
  4. Divide the junction area by the insulation lambda value only

Explanation

Linear thermal transmittance is obtained from a 2D or 3D heat-flow calculation, comparing the modelled junction against a reference where the adjoining elements are extended without the bridge. Certified junction details and catalogues of psi values are often used to avoid recalculation.

Question 40Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A steel beam penetrates the insulated envelope of a Passive House. How should the designer best address the resulting thermal bridge?

  1. Interrupt the penetration with a thermally broken connection or move the structural path outside the insulation line Correct answer.
  2. Add a vapour barrier directly on the steel to stop heat flow
  3. Increase the thickness of the insulation on the warm side only
  4. Ignore it because steel has a high thermal conductivity

Explanation

Because steel conducts heat strongly, a penetrating beam can create a severe bridge and cold internal surfaces. The robust solution is to break the thermal path, for example with a thermally broken connector, or to keep the structure outside the insulated envelope.

Question 41Building envelope: thermal insulation, thermal bridges, airtightness and construction details

During a blower door test on a completed Passive House, the measured n50 is 0.6 but a smoke pencil reveals a leak at a window reveal. What is the most appropriate interpretation?

  1. The overall result meets the target, so no further action is warranted
  2. The smoke pencil result proves the ventilation system is undersized
  3. The overall result meets the target, but the localised leak should still be located and sealed because it indicates a discontinuity in the airtightness layer Correct answer.
  4. The leak must mean the n50 value is invalid and the test should be discarded

Explanation

A compliant n50 does not guarantee a continuous airtight layer; local leaks can still cause moisture problems and comfort issues at specific junctions. Best practice is to use the test to find and seal discontinuities even when the global figure passes.

Question 42Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Which construction detail most reliably maintains airtightness where a partition meets an external wall in a timber-frame Passive House?

  1. Rely on the plasterboard finish alone to provide the seal
  2. Seal only the external windtight membrane at the junction
  3. Leave a small gap to allow the frame to move
  4. Bond the internal airtight membrane continuously across the junction with a taped or clamped connection before the partition is closed Correct answer.

Explanation

The airtight layer must be continuous and structurally decoupled from movement, so the membrane is carried across the junction and taped or clamped to the partition's airtight layer. Plasterboard alone is not a reliable, verifiable airtight seal.

Question 43Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Why is a capillary-active or vapour-open internal lining sometimes preferred on the inside of a masonry wall in a Passive House refurbishment?

  1. It eliminates the need for any insulation
  2. It provides a permanent vapour-tight seal
  3. It allows incidental moisture to be absorbed and released, supporting drying towards the interior Correct answer.
  4. It raises the U-value of the wall to Passive House levels on its own

Explanation

Capillary-active linings such as suitable mineral plasters or boards can buffer small amounts of moisture and release it, helping the wall dry inward where outward drying is restricted. They are used together with insulation, not instead of it.

Question 44Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A designer specifies a window installed in the insulation layer rather than flush with the masonry. What is the main thermal benefit?

  1. It increases the glazing solar heat gain coefficient
  2. The frame sits in the warmer zone, reducing the linear thermal bridge at the reveal and raising the internal frame surface temperature Correct answer.
  3. It makes the window airtight without any sealing tape
  4. It removes the need for a window sill

Explanation

Positioning the window towards the insulation line keeps the frame within the warm zone, which reduces the reveal thermal bridge and keeps internal frame surfaces warmer, lowering condensation risk. Airtight sealing and weather sealing are still required.

Question 45Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Which statement correctly distinguishes a repeating thermal bridge from a non-repeating one?

  1. Repeating bridges are always point bridges, while non-repeating bridges are always linear
  2. Repeating bridges occur regularly within a construction layer, such as mortar joints or studs, while non-repeating bridges occur at specific junctions such as corners and penetrations Correct answer.
  3. Repeating bridges occur only at building corners, while non-repeating bridges occur in the middle of walls
  4. Repeating bridges are ignored in the Passive House balance, while non-repeating bridges are always counted

Explanation

Repeating bridges are periodic features within a layer, for example timber studs or mortar joints, and are often folded into the corrected U-value of that element. Non-repeating bridges are individual junctions and penetrations, quantified with psi or chi values.

Question 46Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A wall assembly has a calculated U-value of 0.13 W/(m2K) but includes stainless-steel masonry ties. How should the effect of the ties be treated?

  1. Double the U-value for all metal fixings regardless of type
  2. Ignore the ties because they are small
  3. Reduce the U-value because metal improves thermal resistance
  4. Apply a correction that increases the U-value to account for the repeating point bridges of the ties Correct answer.

Explanation

Metal fixings create repeating point bridges that slightly worsen the thermal performance, so the U-value is corrected upward by a calculated amount that depends on fixing type, diameter and density. The correction is specific, not a blanket doubling.

Question 47Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Why is the airtightness layer typically placed on the warm side of the insulation in a cold climate?

  1. So that it increases the thermal resistance of the insulation
  2. So that any moist air leaking through the layer is not driven into a cold zone where it could condense Correct answer.
  3. So that it can serve as the structural sheathing
  4. So that the layer can act as the external rain screen

Explanation

Placing the airtight layer on the warm side means that if moist indoor air leaks, it is less likely to reach cold surfaces where it could condense. This position also complements the internal vapour control function.

Question 48Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A retrofit adds internal insulation to a solid masonry wall. Which risk must the designer assess most carefully?

  1. Interstitial condensation and reduced drying potential at the cold masonry-insulation interface Correct answer.
  2. Reduced compressive strength of the floor slab
  3. Increased solar overheating caused by the internal insulation
  4. Loss of airtightness in the roof space

Explanation

Internal insulation moves the dew point towards the masonry-insulation interface and reduces the wall's ability to dry inward, raising the risk of interstitial condensation and frost damage. A hygrothermal assessment and suitable materials are needed.

Question 49Building envelope: thermal insulation, thermal bridges, airtightness and construction details

Which of the following best explains why a thermal bridge can cause mould even when the average internal surface temperature of the wall is acceptable?

  1. The bridge increases the internal air temperature too rapidly
  2. The local surface temperature at the bridge can fall below the dew point while the rest of the wall stays warmer Correct answer.
  3. The bridge blocks the ventilation system from operating
  4. The bridge raises the relative humidity of the whole room uniformly

Explanation

Mould risk depends on local surface temperature and local humidity, not the wall average. At a thermal bridge the surface can drop below the dew point and stay damp even when the general wall surface is fine.

Question 50Building envelope: thermal insulation, thermal bridges, airtightness and construction details

A designer must verify that a certified Passive House junction detail matches the actual construction. Which action is most appropriate?

  1. Replace the certified detail with an assumed psi of zero
  2. Check that the built layers, insulation thicknesses and materials match the certified detail and recalculate psi if they differ Correct answer.
  3. Assume the certified value applies regardless of the built construction
  4. Use the certified psi but increase the insulation thickness by half

Explanation

A certified junction value is only valid for the exact construction it was calculated for. If layers, thicknesses or materials change on site, the psi value must be recalculated to remain defensible in the balance.