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Improved U-Value targets for new dwellings under AD Part L1 2021

The new Approved Document Part L1 2021 has further reduced the limiting U-Values for thermal elements, meaning many common methods of construction will no longer be possible.


Whilst this is important step forward in reducing CO2 emissions, it will present new challenges to house builders.


New Limiting U-Values


Below is a table for comparison between 2016 and 2021 Limiting U-values for new fabric elements and air permeability in new dwellings (extracted from Table 1.4 of Approved Document Part L1 2021)

Fabric Element

Part L (2016) Maximum U-value W/(m2.K)

Part L (2021) Maximum U-value W/(m2.K)

Roof

0.20

0.16

Wall

0.30

0.26

Floor

0.25

0.18

Party Wall

0.20

0.20

Swimming Pool Basin

0.25

0.25

Windows

2.00

1.60

Rooflight

2.00

2.20

Doors

2.00

1.60

Air Permeability

10 m3 /(h·m2 )@50Pa

8 m3 /(h·m2 )@50Pa

What Does This Mean?


Whilst it's difficult to to say exactly what these new limiting values mean to everybody, it is most certainly likely to see the end of partially filled 100mm cavities, aluminium windows and doors that aren't thermally broken and floor constructions with only 75mm EPS insulation.


Want To Know More About The Other Important Changes To The 2021 Regulations?


To see all our guidance articles on the changes to the Approved Documents 2021, make sure your visit our 2021 Buildings Regulations page.


Stay Up To Date


With some many changes as a result of the New Part L, Part F and Part O, make sure you join our members area so every time we release a new guidance article it goes straight into your email inbox. Sign up now and join here.

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