FAQs - Frequently asked questions

There isn't one U-value that applies to every flat roof.

The required performance depends on factors including whether the project is a new build or refurbishment, the type of building, the construction and the applicable Building Regulations and design requirements.

For example, the 2026 Approved Document L Volume 2, covering buildings other than dwellings in England, gives a maximum U-value of 0.18 W/m²K for roofs for new or replacement elements. For new dwellings, the 2026 Volume 1 gives a limiting U-value of 0.16 W/m²K for all roof types.

However, a project may require a different target U-value, so the required performance should be established by the project designer or energy assessor.

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