1.01Fundamentals
On-site renewable electricity
Allocate generation only where it connects on the consumer side of the primary meter serving the assessed building or part.
England and Wales · Issue 9
NDEA Conventions Guide
Search the conventions using a site situation or question. Guidance is linked to the specific Issue 9 conventions that support it.
Ask the conventions ↓- Document
- Non-Domestic EPC Conventions
- Issue
- 9
- Latest implementation date
- 1 July 2024
Conventions guidance
Ask about a site situation
Use ordinary language. The response identifies the most relevant conventions, explains the action to take and shows connected checks.
Examples
Reference index
Browse conventions
41 conventions shown
2.02Evidence
Use of defaults
Use a software default only when no convention or more specific building information is available.
2.03Fabric
Air permeability
Select the Issue 9 permeability value by test evidence, age, size and construction risk.
2.04Fundamentals
SBEM weather location
For England, use the official postcode-area lookup; Wales uses the software-assigned Cardiff location.
2.05Evidence
Planning use class
The assessor does not establish the authorised use class; use a suitable supplied source or the observed building type.
2.06Evidence
As-built data
An EPC based on design-team documents must rely on as-built information, not design-only information.
2.07Evidence
Acceptable documentary evidence
Documents are usable only when there is a demonstrable link to what was observed on site.
2.09Lighting
High-frequency T8 lamps
Screen flicker can evidence low frequency, but cannot by itself prove high-frequency operation.
2.10HVAC
Electric shower with another DHW source
Treat the arrangement as bivalent when an electric shower shares the room with another non-instantaneous-electric DHW source.
2.11HVAC
Hydrotreated vegetable oil (HVO)
Model an HVO heat generator using biomass as the closest fuel and adjust the established gross efficiency.
2.12HVAC
Incomplete or condemned HVAC
Treatment depends on which components remain and whether the system is condemned or robustly decommissioned.
3.02Fabric
Party-wall adjacency
Assume adjoining buildings are conditioned unless they are in Planning Classes B2-B8, which are assumed unconditioned.
3.03Fabric
Window frame factor
Establish an appropriate frame factor for every distinct window or roof-light set; do not retain 0.10 without checking.
3.07Fabric
U- and Km-values
Use library or inference values unless accurate specific values are available from a suitable source.
3.08Fabric
Strongly ventilated spaces
Use strongly ventilated only as an alternative to unheated adjoining space where permanent high ventilation is present.
3.09Fabric
Transparent curtain walling
The SBEM “curtain walling” library entry describes the opaque construction, not the glazing within it.
3.13Fundamentals
Sales or eating/drinking
For a small takeaway, use eating/drinking only for an internal area specifically provided with tables or counters and chairs.
4.01Geometry
Light wells
Treat the walls of a light well as external envelopes.
4.02Geometry
Atria
All atria are a Level 5 NDEPC assessment feature.
4.04Geometry
Measurement accuracy
Record site measurements and calculated software inputs to at least two decimal places.
4.05Geometry
Roofs with multiple components
Use the area exposed to conditioned space and model each pitched component according to whether a horizontal internal ceiling exists.
4.07Geometry
Daylit zoning
Evaluate every zone for significantly different daylight and subdivide when automatic daylight zoning is not used.
4.08Geometry
A zone within a zone
Model the floor envelope above an inner zone for heat transfer and thermal mass, but count it as EPC floor area only when permanently accessible and usable.
4.09Geometry
Low zone height
Where the convention produces a zone height below 1.2 m, enter 1.2 m but leave every envelope at its actual size.
4.10Geometry
Foundation area
Foundation area is total conditioned floor area divided by the maximum relevant storey count.
5.01HVAC
Electric power factor
Leave power factor at <0.9 unless a correction device or other compelling evidence supports a change.
6.03HVAC
Electric room heaters
Any fixed electric room heater is entered with an amended efficiency of 1.00.
6.04HVAC
LTHW boiler efficiency
Follow the evidence hierarchy before using an SBEM boiler default.
6.05HVAC
Electric hot water storage
Use “instantaneous” only where the electric DHW system has no storage at all.
6.06HVAC
DHW losses and unknown systems
Enter storage losses for every storage system, preferring evidenced monthly loss over volume and insulation.
6.08HVAC
Mechanical exhaust SFP
When specific fan data is unavailable, use the Issue 9 system-type and regulation-age table — never an arbitrary value.
6.11HVAC
Zones without fixed conditioning
Assess as seen and follow the hierarchy for shell-and-core, indirect conditioning and activities allowed to be unconditioned.
6.12HVAC
Kitchen extraction
Include all kitchen extraction or mechanical ventilation to represent the additional conditioning energy.
6.13HVAC
Indirectly conditioned zones
Treat a zone without fixed conditioning as indirectly conditioned when at least 50% of its surrounding envelope adjoins directly conditioned space.
6.14HVAC
Shop units in shopping centres
Model local systems and central air according to whether the central supply is unconditioned, tempered or fully conditioned.
6.15HVAC
Bivalent system proportions
Determine heating-load shares zone by zone and use design evidence where available.
7.01Lighting
Lighting input hierarchy
Choose the most evidence-rich lighting route available; wattage and lux must come as a valid pair.
7.03Lighting
Mixed lighting in a zone
Separate display lighting and proportion mixed general-lamp types where a simple location split is impracticable.
7.04Lighting
Assumed display lighting
Where the selected activity assumes display lighting but none is present, align its efficiency with the general lighting.
7.05Lighting
Missing lamps
When a fitting is present without a lamp, select CFL if it accepts CFL; otherwise select the least efficient compatible lamp.
7.06Lighting
2D lamps
Enter a 2D lamp as T5 only when technical information or visual inspection specifically identifies T5 technology.
Learning
Conventions trainer
Complete a five-question practice session based on Issue 9. Topics are mixed, explanations are shown after each answer and missed conventions are scheduled for review.
01 Retrieval before reveal02 Immediate explanation03 Spaced review of misses
Device progress0answered0%accuracy
You inspect a retail unit. The boiler remains in place, but every radiator and heater has been removed from the sales zone.
How should the sales zone be treated?
Official document extracts
Diagrams and tables
These figures are reproduced from the official Issue 9 PDF. Select a figure to view it at a readable size. Text descriptions are provided for screen-reader users.
4.08Zone within a zoneOfficial page 15
10.02Assessment level decision flowchartOfficial page 31
10.03Horizontal dimensionsOfficial page 33
10.03Intermediate floors and sloping spacesOfficial page 36
10.03Mono-pitched and curved roofsOfficial page 37
10.04Local mechanical exhaust ratesOfficial page 39
10.06Roofs with multiple componentsOfficial page 42
10.07Zones without fixed conditioning equipmentOfficial page 43
Source and scope
About this guide
This prototype condenses the official Non-Domestic EPC Conventions for England & Wales, Issue 9. It covers high-frequency field decisions and the six conventions implemented on 1 July 2024.
It is a learning and reference aid, not a replacement for the full conventions, approved software guidance, Part L, scheme instructions or professional judgement.