Skip to Content

EWI Planning & Building Regulations Guide (UK) (2026 Edition)

Everything You Need to Know About EWI Compliance in the UK for 2026

For most UK dwellings under 11m, External Wall Insulation (EWI) is considered Permitted Development provided the finish is "similar in appearance" to the original building. However, Building Regulations approval is a legal requirement. Under Approved Document L (2021/2023), the target U-value for retrofitted walls is 0.30 W/m²K. This guide details the current 2025 standards and prepares you for the Future Homes Standard 2026.

Planning Permission: Do You Need It?

While "Building Regulations" cover how you build, "Planning Permission" covers if you can build.

Permitted Development (PD)

In the majority of cases for detached, semi-detached, and terraced houses, EWI falls under Permitted Development. You generally do not need to submit a full planning application if:

  • Similar Appearance: The final render color and texture are similar to the original or the neighbouring houses.
  • Projection Limits: The insulation does not project more than 16cm (160mm) from the existing wall.
  • Boundary Control: The work stays entirely within your property boundary (curtilage).

When You MUST Apply for Planning Permission:

  • Conservation Areas & AONBs: If your home is in a protected area, any change to the facade usually requires permission.
  • Listed Buildings: You must apply for Listed Building Consent. Installing EWI on a listed building without consent is a criminal offense.
  • Highway Encroachment: If your insulation would overhang a public pavement or highway, you potentially need a full planning.
  • Material Change: If you are changing a red-brick house to a bright white or coloured render, many councils consider this a "material change" that requires approval.

Building Regulations - Fire (B), Energy (L) and Ventilation (F)

For houses below 11 metres (typically 2–3 storeys), you must comply with these specific documents.

A. Approved Document L: Conservation of Fuel and Power (2021 Edition with 2023 Amendments)

  • The 25% Rule (Section 4): If you are renovating more than 25% of a wall’s surface area, you are legally obligated to upgrade that wall's thermal performance (AD L, Vol 1, Section 4.2).
  • The U-Value Target: For a retrofit (existing wall), you must achieve a U-value of 0.30 W/m²K (Table 4.2, p. 21).
  • New Extensions: If your EWI is for a new extension, the target is stricter: 0.18 W/m²K (Table 4.1, p. 20).

B. Approved Document B: Fire Safety (Volume 1: Dwellings)

For buildings under 11m, the rules are designed to prevent "surface spread" of flame.

  • Material Choice: You can use Fire-Retardant EPS (Expanded Polystyrene) on houses under 11m. However, it must be part of a "system" that is BBA-certified.
  • The 1-Metre Rule: If your wall is within 1 metre of a boundary (e.g., a narrow alley between houses), the external surface must be Class B-s3, d2 or better (Section 10).
  • Fire Breaks: Although not always strictly mandatory for low-rise houses, RenderStore recommends horizontal Mineral Wool fire breaks at every floor level and around window openings to stop fire from spreading behind the insulation.

C. Approved Document F: Ventilation (2021 Edition)

This is critical. Sealing your house with EWI stops "natural leakage." To prevent mould and rot, you must follow Requirement F1.

  • "No Worse" Rule: You must prove that adding insulation has not made the ventilation worse (Section 3.6).
  • Mandatory Upgrades: Usually, this means installing Trickle Vents in windows (minimum 5000mm² for habitable rooms) or a Continuous Mechanical Extract (cMEV) system to ensure fresh air circulation (Table 1.7).

Downloading Official Reference Documents

To support your Building Control application, you can download the full official PDF documents here:

Looking Ahead: The 2026 Future Homes Standard 

While the above rules are the current law in 2026, the government is transitioning toward the Future Homes Standard (FHS).

  • Net-Zero Ready: By 2026, the push will move from "efficient" to "Net-Zero Ready."
  • Stricter Targets: We anticipate that retrofit U-values may eventually align with new-build targets (0.18 W/m²K).
  • Digital Records: The "Golden Thread" of information (knowing exactly what is inside your walls) will become standard for all home sales.