1. The document outlines changes to Part L and NCM modelling guidelines for Part L 2021 compliance in England, including a primary energy target, nearly zero energy building requirement, and updated notional building specifications and carbon factors. 2. Key changes to the notional building include lower U-values, inclusion of solar PV, secondary hot water circulation where specified, and revised lighting and fan energy calculations. 3. New monthly carbon factors for grid electricity see a 62-82% reduction compared to Part L 2013 values.

1. Part L & O 2021
Revision Update
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What these changes mean for designers

2. Speakers
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Richard Tibenham,
Business Development
for IES
Eric Roberts
Business Development
Manager for IES
Michael Pollock
Consultancy Manager
for IES

3. Introduction to Part L
Eric Roberts
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4. Introduction
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This approved document takes effect on 15 June 2022 for use in England. It does not apply
to work subject to a building notice, full plans application or initial notice submitted before
that date, provided the work for each building is started before 15 June 2023.
EPC’s for existing buildings and buildings subject to Part L 2021 will require to be assessed
under the new regulation from 15 June 2022. New buildings which are assessed against the
Part L2A 2013 regulation will remain able to lodge EPC’s under the Part L2A 2013
methodology upon completion.

5. Part L / NCM Modelling Guide Key Changes
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1. Primary energy target introduced.
2. New Notional Building specifications target a 27% reduction in CO2 emissions as compared to ADL2A 2013.
3. ‘Where a building is erected, it must be a nearly zero-energy building’.
4. New classifications for high & low hot water demand for certain activity types (e.g. sports centre changing facilities).
5. Notional building now includes solar PV.
6. Notional building now includes DHW secondary circulation & storage where specified.
7. New set of fuel carbon factors introduced, including monthly variable grid-electric factors.
8. Revised approach for determining lighting illuminance in the notional building.
9. Revised approach for accounting for primary energy, accounting for onsite energy generation.
10. Upgrade to TRY2016 weather data sets.
11. Updated HVAC options in the actual building.
12. Revised approach for calculating fan energy in demand-controlled systems.

6. Notional Building Fabric Parameters
Part L 2021 Notional Building vs Part L 2012 Notional Building
Element Type
Part L 2021 Vol2
(The Building Regulations 2010. 2021 edition)
Part L2A 2013
(The Building Regulations 2010. 2013 edition
incorporating 2016 Amendments)
Construction Fabric Notional U-Values
Side-lit & unlit activities Top-lit activities Side-lit & unlit activities Top-lit activities
Roofs 0.15 0.18 0.18
Exposed Walls 0.18 0.26 0.26
Exposed floors 0.15 0.22 0.22
Windows 1.40 - 1.60
Rooflights - 2.1 1.80
Vehicle access /large doors 1.30 1.50
Pedestrian & high usage doors 1.90 2.20
Air Permeability (m3/(m².hr)@50Pa
Less than or equal 250 m2 3 5 5 7
Greater than 250 m2 and less than 3,500 m2 3 5 3 7
Greater than or equal to 3500 m2 and less than 10,000 m2 3 5 3 5
Greater than or equal 10,000 m2 3 5 3 3
Glazing Specifications
g-value: 29%
Light transmittance: 60%
Exposed facades will have
windows with area that is
the lesser of either: 1.5m
high × full facade width OR
40% of exposed facade area
g-value: 40%
Light transmittance: 71%
12% of exposed roof area
will be made up of roof-
lights
g-value: 40%
Light transmittance: 71%
Exposed facades will have
windows with area that is the
lesser of either: 1.5m high ×
full facade width OR 40% of
exposed facade area
g-value: 55%
Light transmittance: 60%
12% of exposed roof area will
be made up of roof-lights

7. Notional Space Heating Systems
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Part L 2021: Part L 2013:
(fuel oil)
(grid electricity)
(natural gas)

8. Notional DHW Heating Systems
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Part L 2021: Part L 2013:
(natural gas)
(grid electricity)
(fuel oil)

9. Other Notable Changes
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1. Primary energy target introduced.
2. PV is now applied to notional building based on an algorithm accounting for foundation area, conditioned area and
number of floors.
3. The notional building now accounts for a secondary circulation loop and hot water storage if specified. Loop length and
storage capacity are based on floor area. Heat losses of 8W/m are accounted for.
4. The general lighting in the notional building is based on lighting with an efficacy of 95 luminaire lumens per circuit-watt,
and the resulting power density (W/m²) will vary as a function of the geometry of each zone modelled.
5. Demand control of ventilation will now also affect the auxiliary energy. Where there is demand control of ventilation, the
auxiliary energy calculation will use a pro-rated value for the maximum fresh air rate.
6. Default thermal non-repeating bridging is increased from 10% to 25% of rated element U-Value.

10. VE 2022 Part L 2021 Interface
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11. Part L 2021 Case Studies
Richard Tibenham
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12. Part L NCM Weather Data
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 Part L 2013 – TRY05 data.
 Part L 2021 – TRY16 data.
 Nottingham TRY16 data;
 More sub-zero hours.
 Fewer hours >14⁰C.
 More hours >28⁰C.

13. Part L NCM Weather Data
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 Part L 2013 – TRY05 data.
 Part L 2021 – TRY16 data.
 London TRY16 data;
 More hours <6⁰C.
 More hours 18-23⁰C.
 Fewer hours >23⁰C.

14. Part L NCM Carbon Factors
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Month Grid-Electricity Carbon Factor
Part L 2013 Carbon Factor
(kgCO2/kWh)
Part L 2021 Carbon Factor
(kgCO2/kWh)
(EXCEPT PV)
Part L 2021 Carbon Factor
(kgCO2/kWh)
(PV)
Jan 0.519 0.163 0.196
Feb 0.519 0.160 0.190
Mar 0.519 0.153 0.175
Apr 0.519 0.143 0.153
May 0.519 0.132 0.129
Jun 0.519 0.120 0.106
Jul 0.519 0.111 0.092
Aug 0.519 0.112 0.093
Sept 0.519 0.122 0.110
Oct 0.519 0.136 0.138
Nov 0.519 0.151 0.169
Dec 0.519 0.163 0.197
Month Natural Gas Carbon Factor
Part L 2013 Carbon Factor (kgCO2/kWh) Part L 2021 Carbon Factor (kgCO2/kWh)
Year-round 0.216 0.210

15. Part L NCM Carbon Factors
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Part L 2013
Grid-
electricity
Part L 2013
Natural Gas
Part L 2021
Grid-
electricity
(Except PV)
Part L 2021
Grid-
electricity
(PV)
Natural gas:
2.8%
reduction
Grid-
electricity:
62-82%
reduction

16. Part L NCM Carbon Factors:
General Consequences
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 Grid-electricity incurs far lower calculated CO2 emissions.
 Systems using electricity as a fuel source incur far lower CO2 emissions.
 Energy generation systems which generate electricity (e.g. solar-PV) achieve
far lower CO2 displacement.
 The electricity carbon factor is higher during the winter and lower during the
summer.
 PV electricity generation is incentivised during the winter.

17. Solar PV Carbon Displacement
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90⁰ Inclination
0⁰ Inclination
90⁰ Inclination
0⁰ Inclination
Part L 2013: TRY05 Part L 2021: TRY16
74% average
reduction in
annualised carbon
displacement

18. Solar PV vs. Solar Thermal Carbon Displacement
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Evacuated-tube solar
thermal collector
~70% eff.
Solar PV collector
~20% eff.
Solar PV: 74% avg. reduction in
CO2 offsetting.
Solar thermal: 6% avg.
increase in CO2
offsetting.
(natural gas offsetting).
Part L 2013: 0.519kg.CO2/kWh
Part L 2021: 0.092kg.CO2/kWh
-0.197kg.CO2/kWh
(grid-electric offsetting)
Part L 2013: 0.216kg.CO2/kWh
Part L 2021: 0.210kg.CO2/kWh
(natural gas offsetting)
Carbon offsetting from
solar thermal is now 2.51
times greater than solar
PV per unit of collector
area (when displacing
natural gas).
Solar thermal (2021)
Solar thermal (2013)
Solar PV (2021) Solar PV (2013)

19. Solar PV vs. Solar Thermal Carbon Displacement
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2013 optimum
inclination: ~35⁰
2021 optimum
inclination: ~40⁰

20. Impact on CHP Units
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Part L 2013:
Uses natural gas @ 0.216(kg.CO2)/kWh to export/offset
grid-electricity @ 0.519(kg.CO2)/kWh.
Part L 2021:
Uses natural gas @ 0.210(kg.CO2)/kWh to export/offset
grid-electricity @ 0.111 – 0.163(kg.CO2)/kWh.
Natural Gas In
Electricity Out
Heat Out

21. Impact on CHP Units
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Part L 2013 – Actual Building (No CHP): Part L 2013 – Notional Building (No CHP): Part L 2013 – Actual Building (With CHP): Part L 2013 – Notional Building (With CHP):
3% CO2
reduction
Without
CHP
36% CO2
reduction
With
CHP
CHP CO2 offsetting
Part L 2013: 33% Reduction in
CO2 with CHP unit
Part L 2013 Without CHP Part L 2013 With CHP

22. Impact on CHP Units
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Part L 2021 – Actual Building (No CHP): Part L 2021 – Notional Building (No CHP): Part L 2021 – Actual Building (With CHP): Part L 2021 – Notional Building (With CHP):
5% CO2
increase with
CHP
CHP CO2 offsetting
8% CO2
increase
without CHP
Part L 2021 Without CHP Part L 2021 With CHP
Part L 2021: 3% Reduction in
CO2 with CHP unit
Notional
PV
offsetting

23. Case Study: Student Accommodation
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Construction Fabric U-Values:
 Walls: 0.25
 Floors: 0.15
 Roofs: 0.13
 Windows: 1.81
 Air permeability: 5m3/(m².hr)@50Pa
Space Heating:
 Electric panel heaters
DHW Heating System:
 ASHP SCoP: 3.14. 3,800lts storage + secondary circulation
Ventilation:
 Natural ventilation w/mechanical extract in showers & kitchens
Renewable Energy Generation:
 None

24. Electric (Resistance) Vs. Gas-fired
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Part L 2021: Electric Panel Heaters + ASHP DHW (SCoP 3.14):
Notional Building TER:
Part L 2021: Gas fired LTHW Rads (95% eff.) + Gas-fired DHW (95% eff.)
Actual Building BER: Primary Energy: Notional Building TER:
Actual Building BER: Primary Energy:
Actual
exceeds
Notional by
35%
(2.45kg.CO2/m2)
Actual
exceeds
Notional by
27% (28kWh/m2)
Actual
exceeds
Notional by
14%
(3.24kg.CO2/m2)
Actual
exceeds
Notional by
10% (14kWh/m2)
LTHW gas-fired radiators still outperform electric resistance heating
in BER/TER assessment terms.

25. Electric (Resistance) Vs. Gas-fired
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Part L 2021: Electric Panel Heaters + ASHP DHW (SCoP 3.14): Part L 2021: Gas fired LTHW Rads (95% eff.) + Gas-fired DHW (95% eff.)
Solar PV area required to secure compliance: ~220m2
Areas to focus:
• Reduction in space heating carbon emissions.
• Improved u-values.
• Reduced air permeability.
• Reduced construction detailing psi-values.
Solar PV area required to secure compliance: >110m2
Areas to focus:
• Reductions in space heating & DHW carbon emissions.
• Improved u-values.
• Reduced air permeability.
• Reduced construction detailing psi-values.
• Consider solar thermal.

26. Electric (Resistance) Vs. Electric (Air-to-Water HP)
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Part L 2021: Electric Panel Heaters + ASHP DHW (SCoP 3.14):
Notional Building TER:
Part L 2021: Air-to-Water HP LTHW Rads (SCoP 3.0) & ASHP DHW (SCoP 2.70)
Actual Building BER: Primary Energy: Notional Building TER:
Actual Building BER: Primary Energy:
Actual
exceeds
Notional by
35%
(2.45kg.CO2/m2)
Actual
exceeds
Notional by
27% (28kWh/m2)
Actual
exceeds
Notional by
8%
(0.55kg.CO2/m2)
Actual
exceeds
Notional by
8% (6kWh/m2)
Heat pumps for space & DHW heating offers lowest absolute BER.

27. Electric (Resistance) Vs. Electric (Air-to-Water HP)
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Part L 2021: Electric Panel Heaters + ASHP DHW (SCoP 3.14): Part L 2021: Air-to-Water HP LTHW Rads (SCoP 3.0) & ASHP DHW (SCoP 2.70)
Solar PV area required to secure compliance: ~220m2
Areas to focus:
• Reduction in space heating carbon emissions.
• Improved u-values.
• Reduced air permeability.
• Reduced construction detailing psi-values.
Solar PV area required to secure compliance: <100m2

28. Case Study: Care Home
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Construction Fabric U-Values:
 Walls: 0.23
 Floors: 0.16
 Roofs: 0.17
 Windows: 1.40
 Air permeability: 5m3/(m².hr)@50Pa
Space Heating:
 Gas fired LTHW Radiators. Comfort cooling lounges
DHW Heating System:
 Gas fired. Secondary circulation + 4,000lts storage
Ventilation:
 Natural ventilation in bedrooms. Mechanical extract in en-suites.
Mechanically ventilated corridors
Renewable Energy Generation:
 39kW gas fired CHP unit

29. Solar PV vs. Solar Thermal
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Actual
exceeds
Notional by
>.1%
(0.07kg.CO2/m2)
Notional
exceeds
Actual by 2%
(0.6kWh/m2)
Part L 2021: No CHP. 100m2 Solar PV.
Notional Building TER:
Actual Building BER:
Part L 2021: No CHP. 50m2 Solar Thermal.
Notional Building TER:
Actual Building BER:
Part L 2021 Compliant
TER/BER
Metered Operational Energy Demand:
• Metered energy: 192kWh/m²
• LETI NZC Standard: 55kWh/m²
• UKGBC NZC Offices: 57kWh/m²
‘Where a building is
erected, it must be a nearly
zero-energy building’.
Solar thermal outperforms solar PV per unit of collector area.
(subject to fuel type displacement)

30. Solar PV vs. Solar Thermal
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Part L 2021: No CHP. 100m2 Solar PV. Part L 2021: No CHP. 50m2 Solar Thermal.
Primary Energy: Primary Energy:
Actual
exceeds
Notional by
2%
(3.9kWh/m2)
Actual
exceeds
Notional by
1%
(2.6kWh/m2)

31. Part L 2021 Conclusions:
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 Biggest change to the Part L regulation since the introduction of TER/BER assessments in 2006.
 ‘Floating target’ of Notional Building/Actual Building approach provide an inconsistent message.
Absolute reductions in carbon & energy demand do not always offer merit.
 Gas-fired heating is no longer heavily promoted, but remains a viable option.
 CHP units perform poorly, offering limited benefit.
 Solar PV retains similar relevance in the context of lower grid-electricity carbon factors, but no
longer offers a ‘get out of jail card’.
 Solar thermal returns from relative obscurity to becoming a key technology, particularly when
offsetting gas demand.
 Heat pumps are likely to play a leading role in meeting compliance objectives.
 Mandated performance standard does not ensure ‘near zero energy buildings’.

32. Part O 2021: Overheating
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33. Building Regulations Part O
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 New overheating assessment applicable to all residential buildings EXCEPT hotels.
 Applicable buildings include; dwellings (houses & apartments), care homes, school/college accommodation,
living accommodation for children under 5.
 Option to adopt a ‘Simplified method’ or ‘Dynamic thermal modelling’.
 Dynamic thermal modelling adopts CIBSE TM59 standard as the basis for assessment.
 For ‘Dynamic thermal modelling’, Part O prescribes additional simulation constraints, including assumptions
concerning the control of windows.
 Takes into consideration access, noise, pollution, security protection from falling, distance from window handles,
security & protection guarding, and entrapment (in louvered shutters).
 Assessment assumes that building occupants will be present to operate opening windows. Does not mandate
assessment to assess an ‘unoccupied by day’ scenario.
 Compliance not difficult where overheating risk is considered from a concept stage.
 Avoid excessive glazing to south & west. Consider cooling strategy early on.

34. Consultancy Support
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 Geometric modelling.
 Part L 2021 strategy support, compliance modelling, & EPC
generation.
 Enhance Building Energy Models (CIBSE TM54, NABERS,
BREEAM GN32, & ASHRAE 90.1).
 Detailed HVAC modelling (adopting IES ApacheHVAC).
 Net-zero carbon strategy and compliance modelling (e.g
SFT Standard).
 Part O strategy support & compliance modelling.
 Daylight modelling.
 CFD Analysis.

35.  IESVE PartL(21) – Due Imminently – order now
 sales@iesve.com
 Training Opportunities:
 Online Part L2 Training – 30th June
 Online Part L2 Training – 19th July
 www.iesve.com/training/online-training
 IES Overheating Training in association with Elmhurst
 Online Part O Training - 24th June
 www.elmhurstenergy.co.uk/training/overheating
 Part L Vol1 – IESVE integration with JPA SAP
 www.iesve.com/software/virtual-environment/applications/uk-and-
ireland-regulations/jpa-sap
IESVE Software
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36. Questions?
Thank you
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