Glossary of terms

A

Air permeability: How much air leaks out of a building through gaps in its fabric, measured by an air tightness test. It’s given in m³/(h·m²) at 50 pascals. The limit for a new home in England is 8.0, but the SAP calculation usually assumes a better figure, and that design figure is the one to achieve. Air tightness testing guide →
Approved Documents: Government guidance on how to meet the Building Regulations in England, published in parts such as L (energy), E (sound), F (ventilation), G (water) and O (overheating). Wales has its own Approved Documents, Scotland uses its Technical Handbooks and Northern Ireland uses Technical Booklets.
As-built SAP: The SAP calculation updated at completion with what was actually built, including the air test result. It’s used to produce the on-construction EPC. SAP calculations guide →
ATTMA and iATS: Schemes that air tightness testers register with. Building control expects the test to be done by a tester registered with a recognised scheme such as these. Air tightness testing guide →

B

Blower door test: An air tightness test that uses a fan in a doorway to pressurise the home. It’s one of the two methods accepted for new homes under Part L; the other is the pulse test. Air tightness testing guide →
BPEC: A training body. Many ventilation testers hold its domestic ventilation qualification, which shows they’re competent to test and commission ventilation systems. Ventilation commissioning guide →
BREL report: The Building Regulations England Part L report, produced with the on-construction EPC from the as-built SAP. In Wales the equivalent is the BRWL report. On-construction EPC guide →
Building control: The people who check building work meets the Building Regulations: in England and Wales, your council’s building control team or a registered building control approver. They issue a completion or final certificate once they have the reports they need.
Building warrant: In Scotland, the approval you need from the council before work starts. Design evidence such as SAP and overheating assessments goes in with the application.

C

Completion certificate: The certificate issued at the end of a project once building control is satisfied with the work and the reports. In Scotland you submit a completion certificate with your test reports, and the council has 14 days to accept it.

D

Design-stage SAP: The SAP calculation done from your drawings and specification before work starts, so building control can check the design can meet Part L. SAP calculations guide →
Display Energy Certificate (DEC): A certificate showing a building’s actual energy use, needed for public authority buildings over 250 m² that the public visits often. It’s separate from an EPC, which rates potential performance. Commercial EPC guide →
Domestic Energy Assessor (DEA): An assessor accredited with a government-approved scheme to produce EPCs for existing homes being sold or let. New-build SAP needs an OCDEA instead. Domestic EPC guide →
Dynamic thermal modelling (TM59): A computer model of a home through a hot summer, done to the CIBSE TM59 method. It’s one of the two ways to show a new home meets Part O, and gives more design freedom than the simplified method. Overheating assessment guide →

E

ECO4: An energy-efficiency scheme that uses the PAS 2035 process. It runs in Wales and Scotland until 31 December 2026, and doesn’t cover Northern Ireland. Retrofit assessment guide →
Energy Performance Certificate (EPC): A certificate that rates how energy efficient a building is, from A to G, and lists ways to improve it. You need a valid one before you market a home or commercial building for sale or rent, and it lasts 10 years. Domestic EPC guide →

F

Fittings approach: A way of showing a new home meets Part G by keeping each tap, shower, toilet and bath within a set maximum flow rate or capacity, as an alternative to a full water calculation. Water efficiency calculations guide →
Future Homes Standard: The new energy standard for new homes in England, in force from 24 March 2027 for most new homes. It uses SAP 10.3, and the Home Energy Model will replace SAP later. Read more →

H

Home Energy Model: The calculation method that will eventually replace SAP for new homes, with a changeover period of at least two years after the Future Homes Standard starts. SAP calculations guide →

M

Minimum EPC rating for lets: In England and Wales, privately rented homes and let commercial buildings must have an EPC of at least E unless a valid exemption is registered. There is a confirmed plan for rented homes to reach C by 1 October 2030, which still needs new legislation. Domestic EPC guide →
MVHR: Mechanical ventilation with heat recovery: a whole-house system that supplies and extracts air. Its supply and extract rates must be tested at completion, with the results given to building control. Ventilation commissioning guide →

N

Non-Domestic Energy Assessor (levels 3, 4 and 5): An assessor who produces commercial EPCs. Level 3 covers simpler naturally ventilated buildings, level 4 larger or air-conditioned buildings, and level 5 complex buildings that need detailed computer modelling. Commercial EPC guide →

O

On-Construction Domestic Energy Assessor (OCDEA): An assessor registered with an accreditation scheme to do new-build SAP calculations and on-construction EPCs. Assessors who only do EPCs on existing homes aren’t qualified for this work. SAP calculations guide →
On-construction EPC: The EPC for a newly built or converted home, produced from the as-built SAP calculation and lodged on the government register. Building control will want to see it before signing the work off. On-construction EPC guide →

P

Part E: The part of the Building Regulations covering resistance to the passage of sound. It’s why attached homes, flats and conversions need pre-completion sound testing. Sound insulation testing guide →
Part F: The part of the Building Regulations covering ventilation. It’s why mechanical ventilation in a new home must be tested and the results given to building control within 5 days of the final test. Ventilation commissioning guide →
Part G: The part of the Building Regulations covering water. For water efficiency, it limits a new home in England to 125 litres per person per day, or 110 where a planning condition requires it. Water efficiency calculations guide →
Part L: The part of the Building Regulations covering the conservation of fuel and power. It’s the reason for SAP calculations, on-construction EPCs and air tightness testing on new homes. SAP calculations guide →
Part O: The part of the Building Regulations that requires new homes to be designed so they don’t overheat in summer. It applies to new residential buildings only, not extensions or changes of use. Overheating assessment guide →
PAS 2035: The standard for energy-efficiency retrofit projects, used by government-funded schemes and TrustMark-registered work. Every project starts with a retrofit assessment. Retrofit assessment guide →
Pre-completion sound testing: Tests on separating walls and floors between homes, done when the building is complete apart from decoration, to show they block enough airborne and impact sound to meet Part E. Sound insulation testing guide →
Pulse test: An air tightness test that releases a short pulse of air at low pressure. It’s accepted for new homes in England under the 2021 Part L, alongside the blower door test. Air tightness testing guide →

R

RdSAP: Reduced data SAP: the method used to produce an EPC for an existing home from a survey. Since June 2025, assessors have used RdSAP 10, which records more detail, such as the size of every window. Domestic EPC guide →
Retrofit Assessor: The qualified person who carries out the retrofit assessment at the start of a PAS 2035 project, working under a TrustMark-registered scheme. Retrofit assessment guide →
Retrofit Coordinator: The person on a PAS 2035 project who uses the retrofit assessment to build a medium-term improvement plan, before a designer specifies the measures and TrustMark-registered installers carry them out. Retrofit assessment guide →
Robust Details: A scheme of approved separating wall and floor designs. Many new-build projects can use it instead of pre-completion sound testing, if the plots are registered before work starts. Conversions normally can’t. Sound insulation testing guide →

S

SAP: The Standard Assessment Procedure: the government’s method for working out a home’s energy and carbon performance. SAP calculations show building control that a new home meets Part L. SAP 10.3 is used from the start of the Future Homes Standard. SAP calculations guide →
Set of sound tests: Between two and six individual airborne and impact sound tests, depending on how the homes are built. Building control normally expects a set on the first home of each type, then at least one set per ten more homes of that type. Sound insulation testing guide →
Simplified method: The quicker way to show a new home meets Part O. It checks glazing areas, orientation, shading and how far the windows open, based on whether the site is a moderate- or high-risk location. Overheating assessment guide →

T

Technical Booklets: Northern Ireland’s guidance on meeting its Building Regulations, the equivalent of England’s Approved Documents. For example, Technical Booklet F1 covers energy and still uses SAP 2009.
TrustMark: A quality scheme for work on homes. PAS 2035 retrofit assessors work under TrustMark-registered schemes, and installers on funded retrofit projects are TrustMark-registered. Retrofit assessment guide →

U

UKAS and ANC: Pre-completion sound testing should be done by a testing body with UKAS accreditation or one registered with the ANC scheme. Sound insulation testing guide →

These definitions summarise our guides for England, with notes on Wales, Scotland and Northern Ireland where the terms differ. Always check the current rules with your building control body.