Dashpivot article page – Part L 2023 U values

Part L 2023 U values

Part L 2023 U values

What are Part L U-values?

Part L of the UK Building Regulations, which deals with the conservation of fuel and power, references "U-values" as a key measure of thermal efficiency in buildings.

U-values are a measure of how much heat is lost through different parts of a building's structure, like the roof, walls, floors, and windows.

The lower the U-value, the better the material is at insulating, meaning less heat is lost.

What is the importance of Part L 2023 U-values?

From an environmental perspective, buildings with low U-values contribute significantly to reducing energy consumption. This reduction is vital in the fight against climate change, as it directly correlates with lower carbon emissions. In terms of economic impact, improved insulation, as indicated by lower U-values, leads to decreased energy bills, offering long-term cost savings to property owners.

Furthermore, buildings that boast high thermal efficiency often enjoy increased property values. On a personal level, better-insulated buildings provide enhanced comfort and healthier living environments for occupants, maintaining more consistent internal temperatures and reducing problems associated with dampness and mould. Therefore, the importance of U-values extends beyond regulatory compliance, touching on aspects of environmental sustainability, economic savings, and occupant health and comfort.

What are the Part L 2023 U-values?

For new dwellings, the U-values are as follows:

  • Roofs: 0.11 W/m²K
  • External Walls (including semi-exposed walls): 0.18 W/m²K
  • Floors: 0.13 W/m²K
  • Party Walls: 0.0 W/m²K
  • Windows and Glazed Doors (with more than 60% glazed area): 1.2 W/m²K
  • Roof Windows: 1.2 W/m²K (in vertical position)
  • Rooflights: 1.7 W/m²K (in horizontal position)
  • Opaque Doors (less than 30% glazed area): 1.0 W/m²K
  • Semi-Glazed Doors (30–60% glazed area): 1.0 W/m²K​​.

For new fabric elements in existing dwellings, the limiting U-values are:

  • Roof: 0.15 W/m²K
  • Wall: 0.18 W/m²K
  • Floor: 0.18 W/m²K
  • Swimming Pool Basin: 0.25 W/m²K
  • Window: 1.4 W/m²K or Window Energy Rating Band B minimum
  • Rooflight: 2.2 W/m²K
  • Doors with >60% Glazed Area: 1.4 W/m²K or Doorset Energy Rating Band C minimum
  • Other Doors: 1.4 W/m²K or Doorset Energy Rating Band B minimum​​.

For existing elements in existing dwellings, the U-values are as follows:

  • Roof: Threshold - 0.35 W/m²K, Improved - 0.16 W/m²K
  • Wall – Cavity Insulation: Threshold - 0.70 W/m²K, Improved - 0.55 W/m²K
  • Wall – Internal or External Insulation: Threshold - 0.70 W/m²K, Improved - 0.30 W/m²K
  • Floor: Threshold - 0.70 W/m²K, Improved - 0.25 W/m²K​​.

Additionally, for doors fitted into existing dwellings, from 15 June 2023, they must achieve 1.4 W/(m²K)​​.

These updated U-values reflect a significant step towards higher energy efficiency standards, emphasising low-carbon heating systems and better insulation to minimize heat loss. These changes are seen as pivotal in aligning building regulations with the UK's long-term goal of achieving net-zero carbon emissions from buildings by 2050​​​​.

How should you be documenting your Part L U-values?

Documenting Part L 2023 U-values for compliance with building regulations involves several important steps. First, gather all relevant technical data on the materials used in the building's construction. This data should include specific information about insulation types, windows, doors, and roofing materials, along with the technical specifications provided by the manufacturers that often include U-values.

Engaging a qualified professional, such as a building surveyor or an energy assessor, is crucial for performing accurate U-value calculations. These experts should provide detailed reports outlining their calculations, methodologies, and assumptions. The construction details of the building, including the layered composition of walls, roofs, and floors and any thermal bridging, should be meticulously documented, detailing the thickness and types of materials used with Photographic Evidence captured.

Energy Performance Certificates (EPCs), which show the building's energy efficiency ratings, should be included in the documentation as they are partly based on U-values. Create comprehensive building regulation compliance reports that demonstrate how the building aligns with the required standards, comparing the documented U-values with the standards set out in Part L or other applicable regulations. Use photos of the construction stages to show how the work done matches the energy-efficient designs in a Part L Photographic Evidence report.

Utilising specialised tools designed for U-value calculation and documentation can greatly aid this process. Additionally, building modelling software can be used to simulate and provide detailed reports on thermal performance. Photographic evidence taken during different stages of construction can visually demonstrate the installation of insulation and other key components affecting U-values.

Regular review and checking of the documentation for accuracy and completeness are essential, and consideration should be given to having the documentation independently verified for validation. Once complete, this documentation should be submitted to the relevant building control body as part of the overall building regulation compliance process. Finally, maintaining all documentation for future reference is vital, especially for any renovations or energy efficiency assessments. This documentation is not just a regulatory requirement but also serves as a record of the building's energy efficiency credentials, important for property valuations, energy assessments, and future retrofitting decisions.

Let's have a look at how you can use Photographic Evidence to capture your Part L requirements.

Part L Photographic Evidence

Record Part L 2023 U-Values easier with this Part L Photographic Evidence template

Use Photographic Evidence to show your Part L 2023 U-values compliance

Properly keep track of your Part L compliance of the 2023 U-values with this Part L Photographic Evidence template.

Take photos on site of work being done to show that it matches the design specifications at each stage, avoiding costly rework.

Photos taken via the app have automated timestamps, geotagging, photo markup and smart tags to highlight important information.

Attach photos directly to the fully customisable report that's pre-built with the fields and section you need to capture photographic evidence of your u-values.

Make it easy for your team to request, complete and sign off on Part L compliance

Build digital processes to keep Part L compliant by using a dedicated Part L Photographic Evidence app to help manage your u-Values and Photographic Evidence.

Set up workflows to notify your team when a Part L Photographic Evidence report is due, then when it's completed, a manager gets a notification that it's ready for signoff approval.

Share completed reports in a single click as professionally formatted PDF or CSV with brand colours and company logo.

Reduce double handling of Part L documents by using the Timeline and Register views to see submitted reports in chronological view, or a more detailed spreadsheet-like view.

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Über Nick Chernih

Nick is the Senior Marketing Manager at Sitemate. He wants more people in the Built World to see the potential of doing things a different way - just because things are done one way doesn't mean it's the best way for you.

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