Overcladding an existing building

Many older offices, schools and blocks of flats still have sound structures and tired outside walls.

Overcladding fixes a new outer layer over the wall that is already there. Cladding can add insulation, change how a building looks and protect the wall behind it.

These notes are for building owners, managers and specifiers in England planning that kind of work on a building other than a house.

Overcladding counts as renovating the wall

Approved Document L covers energy efficiency in the building regulations. It treats a new layer of cladding or render on the outside of a wall as renovating that wall.

The whole wall should then be brought up to an improved standard of insulation in two cases. One is when more than half of that wall's surface is renovated. The other is a major renovation, where more than a quarter of the surface area of the whole outer envelope of the building is renovated.

Sometimes the full standard is not technically or functionally possible, or would not pay back within 15 years. The wall should then be upgraded as far as is possible within a 15-year simple payback. When the work is done, a suitably qualified person signs a report on how the design guards against condensation.

GOV.UK holds a 2026 edition of Approved Document L alongside earlier editions. The earlier editions still apply to buildings subject to the earlier standards.

Lettings and energy ratings

Since 1 April 2023, privately rented commercial property in England and Wales has needed an Energy Performance Certificate (EPC) rating of at least E, unless the landlord has registered a valid exemption.

Wall insulation can be part of reaching that rating. There is a separate exemption where the only relevant improvements are wall insulation and written expert advice says they would harm the fabric or structure of the building. It lasts five years.

Fire rules on taller residential buildings

Some buildings have a storey 18 metres or more above the ground and contain flats, an institution or rooms for residential purposes. Hotels, hostels and boarding houses are not included. On these buildings, any material that becomes part of the outside wall must reach class A2-s1, d0 or class A1, with a few listed exemptions.

A material of "limited combustibility" does not meet this rule. Existing materials that are not replaced are not caught by it. The work must still leave the building no less compliant than before, for example in its cavity barriers.

On every building, the fire guidance in Approved Document B still applies to the outside wall.

Higher-risk buildings need approval first

A higher-risk building has at least 7 storeys or is at least 18 metres high. It also has at least 2 homes, or is a hospital or a care home. Building work on one needs approval from the Building Safety Regulator before it starts.

The regulator sorts work on existing higher-risk buildings into category A or category B. Category A includes work involving passive fire safety measures, and external remediation work. It takes up to 8 weeks to assess an application for an existing building, unless an extension is agreed.

Before applying, the regulator expects surveys and checks showing how the work will affect the existing building. Duties under the Regulatory Reform (Fire Safety) Order 2005 need considering too.

For other buildings, building control comes from the local authority or a registered building control approver.

Getting the work under way

If you are unsure whether the work needs building control approval, a building control body can tell you. For a building that is not higher-risk, you can choose your local authority's building control department or a private registered building control approver.

The Planning Portal can find the local planning authority and the building control department for any postcode.