How do I calculate a wall U-value?

Build up layers with thickness and thermal conductivity. The calculator sums thermal resistances (including surface resistances) and returns U = 1/R_total in W/m²K.

What U-value limits apply under Part L?

England Part L 2021 sets limiting U-values for new dwellings and non-domestic work. Use the project's notional or limiting table — this tool is for first-pass screening.

When should I use a full SAP or dynamic model instead?

For EPC submission, overheating analysis, or complex junctions, use accredited software. This calculator is for quick fabric checks during early design.

BuildFlo Design Guide · Thermal · Part L / BS EN ISO 6946

U-value calculator for walls, roofs and floors

Calculate wall, roof or floor U-values and check against Part L limiting values. Free UK U-value calculator for building services and compliance screening.

What this calculator does

U-value helps UK building services engineers with wall, roof, floor, window or door u-value with part l dwelling / commercial check. The calculation follows Part L / BS EN ISO 6946 methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "u-value", "u-value calculator", or "how to u-value", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: W/m²K.

Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about u-value under UK standards.

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Frequently asked questions

How do I calculate a wall U-value?: Build up layers with thickness and thermal conductivity. The calculator sums thermal resistances (including surface resistances) and returns U = 1/R_total in W/m²K.
What U-value limits apply under Part L?: England Part L 2021 sets limiting U-values for new dwellings and non-domestic work. Use the project's notional or limiting table — this tool is for first-pass screening.
When should I use a full SAP or dynamic model instead?: For EPC submission, overheating analysis, or complex junctions, use accredited software. This calculator is for quick fabric checks during early design.