Building envelope

Insulation requirements for commercial and residential buildings

Quick-reference guide to insulation U-value requirements by building element, building type, and work type under Part L of the Building Regulations 2010. Covers wall, roof, and floor insulation options, fire safety considerations for external insulation, and PAS 2030/2035 retrofit standards.

UK-wide
Guide summary

You must insulate walls, roofs, and floors to specific standards when building new properties or renovating. Check the maximum U-values for your building type and work. Notify building control before starting insulation work. External insulation must meet fire safety rules.

  • New non-domestic buildings: walls 0.26, roof 0.18, floor 0.22 W/m²K
  • New homes: walls 0.26, roof 0.16-0.18, floor 0.18 W/m²K
  • Upgrade insulation if renovating over 25% of a wall, roof, or floor
  • Notify building control before starting insulation work
  • External insulation must meet fire safety requirements
  • Use PAS 2030/2035 standards for retrofit work
  • Wales has different rules to England
  • Future standards will require better insulation from 2026
  • Condensation risk assessments required for wall insulation
  • U-values measure heat loss - lower numbers mean better insulation
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UK-wide

Related guides in Premises & Operations

Insulation requirements under Part L

This reference covers insulation U-value requirements for walls, roofs, and floors under Approved Document L of the Building Regulations 2010. Requirements differ depending on the building type (domestic or non-domestic), the type of work (new build, extension, renovation, or replacement of a thermal element), and the building element being insulated.

U-values measure how much heat passes through a building element. A lower U-value means better thermal performance. All U-values below are maximum permitted values for England.

U-value requirements by building element

Non-domestic buildings (Part L Volume 2, 2021 edition)

Domestic buildings (Part L Volume 1, 2021 edition)

Requirements by work type

New builds and extensions

New buildings and extensions must meet the full U-value targets listed above. Actual design U-values may need to be better (lower) than the limiting values to meet the overall target CO2 emission rate for the building. Extensions must meet the same U-value standards as a new build.

Renovation and replacement of thermal elements

When you renovate a thermal element (wall, roof, or floor) beyond specified thresholds, you must upgrade the insulation to current Part L standards under Regulation 23.

Wall insulation options

Choosing between cavity fill, EWI, and IWI

The best approach depends on your existing wall construction, exposure to driving rain, planning constraints, and budget:

  • Cavity wall insulation is the most cost-effective option for existing cavity walls. It is minimally disruptive and typically takes one day. Not suitable for walls with existing moisture problems or in areas of severe exposure without appropriate product certification.
  • External wall insulation (EWI) wraps the building in insulation and a protective render or cladding system. It avoids internal disruption and eliminates thermal bridges, but changes the external appearance. Planning permission may be needed in conservation areas. Fire safety requirements under Part B and the Building Safety Act 2022 apply to external insulation on buildings over 11 metres.
  • Internal wall insulation (IWI) adds insulated dry-lining to the inside of external walls. It does not alter the external appearance (important for listed buildings) but reduces room sizes, requires redecorating, and can create condensation risks if not properly detailed.

Roof insulation

Floor insulation

Fire safety considerations for external insulation

External wall insulation systems on buildings above 11 metres must meet Building Regulations Part B fire safety requirements. Following the Grenfell Tower fire, the Building Safety Act 2022 introduced additional obligations:

  • External wall fire review is required for buildings over 11 metres tall
  • Combustible materials (including certain insulation types) are banned on the external walls of buildings over 18 metres under the Building (Amendment) Regulations 2018
  • Products must achieve a European classification of A2-s1,d0 or better (Class A1 or A2) for buildings over 18 metres
  • For buildings between 11 and 18 metres, a fire risk assessment of external wall systems is still required

Even for buildings below 11 metres, designers and installers should consider fire performance when specifying external insulation materials.

PAS 2030/2035 retrofit standards

If insulation work is funded through a government scheme (such as ECO4 or the Great British Insulation Scheme), it must comply with PAS 2030:2023 (installation standard) and PAS 2035:2023 (retrofit framework). Key requirements include:

  • A retrofit assessment by a qualified retrofit assessor before work begins
  • A retrofit coordinator overseeing the project
  • Work carried out by a TrustMark-registered installer certified to PAS 2030
  • A medium-term improvement plan to avoid unintended consequences (such as condensation or overheating)

Even where PAS 2030/2035 is not mandatory, following the framework is considered best practice for retrofit insulation work.

Official guidance and resources