The short answer
Yes — how close a wall is to the relevant boundary directly affects the cladding fire rules in Approved Document B. The principle is that an external wall close to a boundary must do more to limit fire spread to neighbouring property, so the reaction-to-fire performance demanded of the cladding is stricter. As a broad guide for houses, where a wall is within 1 metre of the relevant boundary, the external surface generally needs to meet a high fire class (limited combustibility), whereas walls further from the boundary can use a wider range of materials. The exact distances, classes and how the boundary is measured are technical and depend on the building, so the position for a specific wall should be confirmed with building control.
Boundary distance is one of the less obvious but important cladding fire controls. This page explains why it matters and the broad principle, while pointing the precise figures to building control.
Cladding fire and boundaries
- Why it matterslimit fire spread to neighbours
- Key principlecloser to boundary = stricter
- Broad rule (houses)within 1m needs high fire class
- Further outwider material choice
- Confirm withbuilding control
Why the boundary matters
A core aim of the fire rules in Approved Document B is to limit the spread of fire from one building to neighbouring property. The external wall facing or close to a boundary is the path by which fire can jump between buildings, so the regulations pay particular attention to it. The closer the wall is to the relevant boundary (broadly, the line dividing your plot from the next, or the centre line of an adjoining road or open space in some cases), the more the wall must resist contributing to and spreading fire. This is why the same house can face different cladding requirements on different elevations — a wall tight to a boundary is treated more strictly than one set well back.
The broad 1-metre principle
For houses, a widely used principle is that the external surface of a wall within 1 metre of the relevant boundary should meet a high reaction-to-fire class (broadly limited combustibility), to reduce the chance of fire spreading across the boundary. Walls that are further than this from the boundary can generally use a wider range of cladding materials, including some combustible options where otherwise acceptable for the building. The detail behind this — the exact distances, the classes required at each distance, the size of permitted unprotected areas, and precisely how the boundary is measured — is technical and varies with building height, use and geometry. Treat the 1-metre point as a broad orientation, not a precise rule for your specific wall.
| Distance to boundary | Broad effect on cladding | Confirm with |
|---|---|---|
| Within ~1m | high fire class generally needed | building control |
| Further from boundary | wider material choice possible | building control |
| Taller buildings | stricter regardless of distance | fire professional |
Indicative principle only; exact distances and classes are set by Approved Document B for the specific building.
It interacts with building height and use
Boundary distance does not act alone. The cladding rules combine distance to boundary with the building's height and use. On taller relevant residential buildings, the ban on combustible materials means external walls must be of limited combustibility regardless of boundary distance, so the boundary relaxation that helps lower buildings does not apply in the same way. On houses, boundary distance is one of the main levers determining what cladding is acceptable on each elevation. Because these factors interact, two seemingly similar walls can have different requirements, and a material acceptable on a rear elevation set back from the boundary may not be acceptable on a side wall close to it.
Practical takeaways
If you are re-cladding and a wall sits close to a boundary, expect the fire requirements on that elevation to be tighter, and plan to use a higher-class (limited-combustibility) material there even if a combustible option would be acceptable elsewhere on the same house. Establish where the relevant boundary lies early, as it affects both the materials and the design. Keep records of the cladding's fire classification for each elevation. And because the precise distances and classes are technical and can change with guidance revisions, use building control to confirm what your specific walls require rather than relying on the broad principle alone — particularly for anything other than a straightforward low-rise house.
Frequently asked questions
What is the 1-metre boundary rule for cladding?
Broadly, for houses, the external surface of a wall within about 1 metre of the relevant boundary generally needs to meet a high reaction-to-fire class to limit fire spread to neighbours, while walls further away can use a wider range of materials. The exact distances and classes are set by Approved Document B and should be confirmed with building control.
Does the boundary rule apply to every elevation of a house?
No. It applies to each wall according to its own distance from the relevant boundary, so different elevations of the same house can have different requirements. A side wall tight to a boundary is treated more strictly than a rear wall set well back.
How is the relevant boundary measured for cladding?
The relevant boundary is broadly the line dividing your plot from the neighbouring one, though for roads and open spaces it can be taken to a centre line in some cases. Because the measurement and its effect are technical, confirm how it applies to your wall with building control.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.