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Part L - Conservation of Fuel and Power

WHAT IS PART L?

Approved document Part L of the building regulations stipulates the minimum U-values for each element of construction, including walls, roof and floor.

Since the specified U-values depend on the type of building construction, Part L is split into four sections:
• L1A New dwellings (Residential new-build)
• L1B Existing dwellings (Residential renovation)
• L2A New buildings other than dwellings (Commercial new-build)
• L2B Existing buildings other than dwellings (Commercial renovation)

MAIN CHANGES TO PART L

A new version of Part L (2013) came into force in March 2014. For the first time, the targets for England and Wales were different, although the methodology remained the same. Changes to the Scottish regulations are due in 2015.
There was no change to the government’s 2016 zerocarbon target for new homes. The only difference here is that European legislation now requires buildings to be nearly zero-energy from 2019.
The good news is that the government doesn’t want its zero-carbon target to hinder economic growth. As a result, the 2013 issue of Part L contains smaller carbon-reduction measures than we expected. CO2 emissions from new dwellings must now be 6% below the standards set in 2010. For new non-domestic buildings, emissions should be reduced by an average of 9%.

PART L MINIMUM U-VALUE REQUIREMENTS

The tables below shows the minimum U-values you should achieve for building fabric in England, Scotland and Wales.

NEW BUILD – RESIDENTIAL L1A

AREA WEIGHTED AVERAGE U-VALUE

 EnglandWalesScotland
External Walls0.30 W/(m2 K) 0.21 W/(m2 K) 0.25 W/(m2 K)
Floors0.25 W/(m2 K)0.18 W/(m2 K)0.20 W/(m2 K) 
Roofs0.20 W/(m2 K)0.15 W/(m2 K)0.18 W/(m2 K)
Air Tightness10 m3 /(hr/m2 ) at 50 Pa 10 m3 /(hr/m2 ) at 50 Pa10 m3 /(hr/m2 ) at 50 Pa

NEW BUILD – COMMERCIAL – L2A

AREA WEIGHTED AVERAGE U-VALUE

 EnglandWalesScotland
External Walls0.35W/(m2 K) 0.35W/(m2 K) 0.27W/(m2 K)
Floors0.25 W/(m2 K)0.25W/(m2 K)0.22W/(m2 K) 
Roofs0.25W/(m2 K)0.25W/(m2 K)0.20W/(m2 K)
Air Tightness10 m3 /(hr/m2 ) at 50 Pa 10 m3 /(hr/m2 ) at 50 Pa10 m3 /(hr/m2 ) at 50 Pa
 

 


EXISTING L1B & L2B (England)

AREA WEIGHTED AVERAGE U-VALUE

ApplicationNEW THERMAL ELEMENT (E.G. KITCHEN EXTENSIONS)  UPGRADING EXISTING ELEMENT (E.G. THERMAL UPGRADE TO SOLID WALL)
WALLS0.28 W/(m2 K) 0.30 W/(m2 K) 
 FLOORS0.22 W/(m2 K) 0.25 W/(m2 K) 
 PITCHED ROOF (RAFTER)0.18 W/(m2 K) 0.18 W/(m2 K) 
PITCHED ROOF (CEILING)  0.16 W/(m2 K)0.16 W/(m2 K) 
 FLAT ROOF 0.18 W/(m2 K) 0.18 W/(m2 K)

EXISTING L1B & L2B (Scotland)

AREA WEIGHTED AVERAGE U-VALUE

ApplicationNEW THERMAL ELEMENT (E.G. KITCHEN EXTENSIONS)  UPGRADING EXISTING ELEMENT (E.G. THERMAL UPGRADE TO SOLID WALL)
WALLS0.19 W/(m2 K) 0.30 W/(m2 K) 
 FLOORS0.15 W/(m2 K) 0.25 W/(m2 K) 
 PITCHED ROOF (RAFTER)0.15 W/(m2 K) 0.25 W/(m2 K) 
PITCHED ROOF (CEILING)  0.13 W/(m2 K)0.25 W/(m2 K) 
 FLAT ROOF 0.15 W/(m2 K) 0.25 W/(m2 K)
 

EXISTING L1B & L2B (Wales)

AREA WEIGHTED AVERAGE U-VALUE

ApplicationNEW THERMAL ELEMENT (E.G. KITCHEN EXTENSIONS)  UPGRADING EXISTING ELEMENT (E.G. THERMAL UPGRADE TO SOLID WALL)
WALLS0.21 W/(m2 K) 0.21 W/(m2 K) 
 FLOORS0.18 W/(m2 K) 0.18 W/(m2 K) 
 PITCHED ROOF (RAFTER)0.15 W/(m2 K) 0.15 W/(m2 K) 
PITCHED ROOF (CEILING)  0.15 W/(m2 K)0.15 W/(m2 K) 
 FLAT ROOF 0.15 W/(m2 K) 0.15 W/(m2 K)
 

AIR TIGHTNESS TESTING

Why is Air Tightness testing needed?
The combination of insulation, with the reduction of air leakage significantly reduces heat losses, reducing CO2 emissions. Consequently Air Tightness testing is required under Building Regulations Approved Document L1A. The results are used in the energy assessment (SAP) of the building which is a tool for demonstrating compliance.

What is tested?
The rate at which air escapes the building. In order to pass, the following need to be achieved:
• Building Regulations ADL1a: 10m3 /(h/m2 ) at 50Pa
• Best practice: 4m3 /(h/m2 ) at 50Pa
• SAP standard: 6m3 /(h/m2 ) at 50Pa

How many tests are needed?
• To meet minimum standards, on each development an air pressure test should be carried out on three units of each dwelling type or 50% of all instances of that dwelling type, whichever is less
• The specific dwelling should be selected by a Building Control Body in conjunction with the tester
• Approximately 50% of the tests should be carried out at the completion of the first 25% of that dwelling type
• On small developments of two or fewer, test all the properties or prove a satisfactory result on another dwelling of the same type constructed by the same builder within the previous year
• A default of 15m3 /(h/m2 ) at 50Pa can be claimed for energy assessments on developments of less than two properties

How is testing done?
All trickle vents and sources of designed ventilation, are sealed. A large door mounted fan is used to de-pressurise the building. The rate at which air escapes is measured and a rating is determined taking into account the size and volume of the building against a benchmark.