ANSWER: OPTION 2

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

 Please explain your reasoning.

• Option 2 is a more ambitious and credible step towards Net Zero

• Option 2 aligns more closely with the building performance achieved by certified AECB CarbonLite & Passivhaus projects. These standards deliver affordable warmth in climate resilient, decarbonised homes.

• Option 2 sets Wales on a meaningful trajectory towards the 2025 and 2030 carbon-reduction targets, focusing on the reduction of energy demand as the stated priority for development in Welsh Government’s Energy Hierarchy for Planning (Planning Policy Wales 12).

• Option 1 delivers weaker fabric standards than AD: L (Wales) 2022, relying on additional PV as a sticking plaster to reach compliance. This could create homes with poorer fabric efficiency, higher running costs and lower resilience to energy price fluctuations and extreme weather.

• Option 2 invests in the building envelope as a lower-risk, longer-term and more equitable route to reducing energy demand, cutting bills and improving occupant comfort and health. 

• A robust, fabric-first standard is critical to delivering affordable warmth and safeguarding public trust in a Just Transition to Net Zero.

  ANSWER: NO 

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

 Please explain your reasoning or how these concerns could be overcome in the future.

• Ventilation systems safeguard occupant health and protect the building fabric. ‘Natural’ ventilation pairing trickle vents with intermittent extract ventilation cannot reliably achieve healthy indoor air conditions.

• Intentionally leaky building fabric does not reliably deliver good indoor air quality but draughty homes do cause thermal discomfort.

• Energy recovery is beneficial, but secondary to ensuring indoor air quality, moisture control and comfort. This principle should be treated as a fundamental performance requirement, comparable to safety standards in fire protection: ventilation simply must work, every time.

• All new homes should be equipped with proven, correctly designed, installed and commissioned ventilation systems that are fit for purpose. 

• Passivhaus designers and practitioners have decades of experience delivering balanced mechanical ventilation systems that perform reliably, providing excellent indoor air quality, comfort and low energy use. The technology, design guidance and quality assurance processes are well established. Only minor updates to Approved Document F - notably around acceptable noise levels and total system pressure loss - would be required to ensure consistent industry delivery.

  ANSWER: NO 

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

 Please explain your reasoning.

• Wales encompasses a wide range of climatic conditions - from mild coastal zones to colder upland regions - and using a Cardiff-only dataset fails to reflect the diversity of heating demand across the country.
• A single weather file risks regional bias and inconsistency with other regulatory and design methodologies: both MCS heat pump sizing and overheating calculations rely on localised weather data. Alignment would ensure coherent, robust and transparent compliance across Wales.
• Accurate local weather data is essential for correctly sizing low-carbon heating systems such as heat pumps. Peak heat loads vary significantly across Wales and underestimation can lead to undersized systems, reduced comfort and loss of confidence in low-carbon technologies.
• For standard dwellings with weaker fabric performance, a single southern climate file would underestimate heating needs in colder regions and result in a less equitable and less resilient outcome.
• Zonal or location-specific climate data should be applied to notional dwelling calculations to support both fabric-first principles and the effective deployment of low-carbon heating technologies.

  ANSWER: YES

  ANSWER: UNSURE

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Please explain your reasoning.  

• Renewable energy generation contributes to decarbonisation but must not be implemented at the expense of fabric-first building efficiencies. 

• Including PV in the notional dwelling allows trade-offs between fabric and generation: weaker envelopes comply by adding more PV. This fails to deliver the same long-term occupant benefits of energy efficiency, resilience and comfort achieved by investing in the fabric.

• If renewables are moved outside the notional building:fabric standards must remain non-negotiable, with no reduction in airtightness, insulation or space-heating demand allowed as a result of PV installation;technical guidance must clarify when PV is genuinely “unsuitable” (roof orientation, shading, design constraints), and how compliance should be calculated in such cases.

• Leaving PV exemptions to Building Control risks limited resources and inconsistent enforcement allowing buildings to comply with minimal fabric improvements. Conversely, keeping PV in the notional building ensures that if PV cannot be installed, compensatory improvements are required - maintaining a robust, fabric-first pathway.

  ANSWER: YES

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• EUI more directly reflects the actual energy performance of a dwelling rather than relying on the relative efficiency rating of DEER. 

• EUI provides clearer insight into expected energy consumption per square metre, helping policymakers, designers and residents understand real operational performance.

• The metric must be robust, transparent and properly defined, including:capturing both regulated and unregulated home energy use;realistic assumptions for occupancy, heating patterns and climate;reflecting the impact of fabric performance and heating system efficiency, rather than allowing high-energy technologies or PV to mask poor building and system design;reflecting actual consumption (import plus on-site usage) minus PV;being verifiable at the as-built stage to help close the gap between design intent and operational outcomes.

• EUI should be defined so that it does not allow on-site renewables to offset fabric or heating inefficiency.

  ANSWER: UNSURE 

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

Please explain your reasoning.

• HEM should only be adopted if demonstrated to be as accurate as the Passivhaus Planning Package (PHPP) in predicting actual energy use, heating demand and occupant comfort. Accuracy and reliability are critical to ensuring compliance targets are meaningful and avoid repeating the performance gaps of previous Building Regulations.

• HEM is currently unproven and not widely validated, presenting a risk of unforeseen issues if adopted as the sole compliance methodology. PHPP has demonstrated model accuracy relies on rigorous alignment between the building provided assumptions and robust input data.

• Recommend PHPP should be formally recognised as an approved compliance methodology alongside any new tools. This would allow designers and assessors to use a quality-assured, evidence-based model, ensuring consistency with best-practice, fabric-first, net-zero-ready design. Fully certified or otherwise verified AECB CarbonLite or Passivhaus projects should be deemed to satisfy Part L, avoiding duplication of modelling. This would align with approaches being developed by the Scottish Government as part of its Scottish Passivhaus Equivalent policy. 

  ANSWER: UNSURE

Repeat the following text (from previous answer)

• Recommend PHPP should be formally recognised as an approved compliance methodology alongside any new tools. This would allow designers and assessors to use a quality-assured, evidence-based model, ensuring consistency with best-practice, fabric-first, net-zero-ready design. Fully certified or otherwise verified AECB CarbonLite or Passivhaus projects should be deemed to satisfy Part L, avoiding duplication of modelling. This would align with approaches being developed by the Scottish Government as part of its Scottish Passivhaus Equivalent policy.

  ANSWER: NO

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Please explain your reasoning.

• Proposed standards appear unnecessarily low: for standard heat pumps the Ecodesign SCOP works out at just 2.75 for space heating. This is unlikely to deliver running costs competitive with gas boilers and risks undermining the decarbonisation and affordability objectives of Part L.
• A higher overall SCOP, including domestic hot water, of at least 3.5 is recommended to ensure running costs are kept low and the systems perform efficiently in practice. 
• Guidance should encourage lower heating flow temperatures as the current upper limit of 55 °C is unnecessarily high. An upper limit of 45 °C would better support efficiency, comfort and integration with low-flow temperature distribution systems.

  ANSWER: NO

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

If No, please explain your reasoning.

• Ventilation systems must be fully integrated with clear guidance on airtightness, ductwork design, commissioning and verification. Correct design, sizing and installation are as important as final commissioning for achieving efficiency, comfort, indoor air quality and occupant wellbeing. 
• The current draft of AD F does not fully address all key issues and some guidance is missing, particularly in Section C4. The following is essential: room noise levels: noise must be calculated in dBA SPL to ensure acceptable acoustic performance in all habitable spaces.duct pressure loss limits: domestic MVHRs are typically tested at 100Pa, which should serve as an effective upper limit.integrated design approach: calculating room noise and duct losses requires early-stage design, not just adjustment at commissioning. Over-reliance on fine-tuning during commissioning cannot compensate for inadequate design.
• Vane anemometers are sufficiently accurate for commissioning systems in Passivhaus homes. Powered flow hoods may offer slight convenience but differences are minor when systems are designed correctly.

  ANSWER: Option 2 – 94% CO2 reduction  

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Please explain your reasoning.

• A strong 2025 uplift is essential to meet 2025 and 2030 carbon-reduction targets, avoid future retrofit costs, and deliver affordable, comfortable and resilient buildings across all new developments.
• To ensure meaningful outcomes and close the performance gap, the 2025 uplift should include:maximised space-heating demand and airtightness targets to address thermal bypass and enhance as-built performance.fabric-first criteria to reduce the scope for trade-offs with renewable generation, ensuring all buildings meet verifiable efficiency standards in operation.robust compliance and verification processes, including recognition of PHPP as an approved compliance methodology for modelling and as-built assessment through CarbonLite or Passivhaus certification.

  ANSWER: NO

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If No, please explain your reasoning.

• cSBEM is less accurate than SAP in predicting actual energy usage. It underestimates space heating demand and overestimates the effect of renewables and high-efficiency plant. It fails to capture the performance of highly insulated, airtight, low-energy or Passivhaus-standard buildings.
• The methodology must evolve to reliably reflect both fabric performance and heating system efficiencies, including distribution and storage losses, avoiding assumptions that allow poor fabric to be offset by renewables or high-performance plant.
• The methodology should: be validated against real-world data, including low-energy and ultra-low-energy buildings, to minimise gaps between predicted and as-built performance; include regulated and unregulated energy uses to give a full picture of energy consumption; recognise PHPP as an approved compliance methodology for designers and assessors, given its internationally recognised track record in predicting actual energy demand..

 Repeat answer to Question 49. 

  ANSWER: YES

  ANSWER: NO

[PLEASE SELECT SOME OF THE FOLLOWING & PUT THEM INTO YOUR OWN WORDS]

If No, please explain your reasoning and provide evidence to support this.

• While reported upfront costs for higher-performance fabric may appear higher, these measures permanently reduce energy demand, improve thermal comfort and minimise running costs, delivering clear benefits to occupants for the lifetime of the building.
• The assessment assumes renewable systems will always perform exactly as expected, which may not be the case in practice, leading to potential gaps between predicted and actual performance.
• Fabric-first approaches support health and wellbeing by maintaining consistent indoor temperatures, minimising draughts and enabling controlled ventilation.
• Adequate ventilation, including MVHR, reduces risks of condensation, mould and indoor air pollution, which can have measurable impacts on public health and associated costs to the NHS. Evidence from Passivhaus projects demonstrates low incidence of indoor air-quality-related health issues when ventilation is correctly designed and commissioned.
• Investing in high-quality building envelopes is a more reliable and cost-effective route to Net Zero than bolt-on renewable technologies and also secures energy efficiency and occupant health benefits.

  ANSWER: YES