The limits
| Rule | Limit | Source |
|---|---|---|
| Depth beyond the rear wall of the original house | No more than 3 m, whatever the house type | A.1(h)(i) |
| Distance to the boundary opposite the rear wall | No part within 7 m | A.1(h)(ii) |
| Roof and eaves | No higher than the highest part of the existing roof; eaves no higher than the existing eaves | A.1(c), (d) |
| Within 2 m of any boundary | Eaves no higher than 3 m | A.1(i) |
| Beyond a side wall | Single storey only, so no two-storey side extension | A.1(j)(ii) |
| Front | Not beyond the principal elevation | A.1(e)(i) |
| Garden coverage | Buildings other than the original house cover no more than 50% of the curtilage, leaving out the original house's footprint | A.1(b) |
| Joined to an earlier extension | The old and new parts together must meet the limits | A.1(ja) |
| Not included | Balconies, verandahs, raised platforms, antennas, chimneys, flues, soil and vent pipes, and changes to the house's roof | A.1(k) |
The larger home extension route (6 m or 8 m) is for single-storey extensions only, so it does not help here (A.1(g)). "Original" means the house as it stood on 1 July 1948, or as built if later (art 2(1)).
The 7 m rule
The enlarged part must not be "within 7 metres of any boundary of the curtilage of the dwellinghouse being enlarged which is opposite the rear wall of that dwellinghouse" (A.1(h)(ii)). In practice, measure from the nearest point of the extension to that boundary. As a hypothetical example, if the original rear wall is 9 m from the back boundary, a two-storey extension could go back no more than 2 m before reaching the 7 m line, even though the depth limit is 3 m. The Order does not say whether exactly 7 m counts as "within 7 metres", so keep a margin or ask the council.
Eaves near the side boundaries
If any part of the extension is within 2 m of a boundary of the curtilage, its eaves must not exceed 3 m (A.1(i)). Unless the eaves of the new part are 3 m or lower, every part of it must stay more than 2 m from the boundaries. Heights are measured from the ground next to the building, using the highest part of the ground where it slopes (art 2(2)).
Conditions you must meet
- Exterior materials of a similar appearance to the existing house (A.3(a)).
- Any upper-floor window in a wall or roof slope forming a side elevation must be obscure-glazed, and non-opening unless the parts that open are more than 1.7 m above the floor of the room (A.3(b)).
- Where the extension has more than one storey, or forms an upper storey on an existing extension, its roof pitch must match the original house so far as practicable (A.3(c)).
Conservation areas and other article 2(3) land
On article 2(3) land, Class A does not cover an enlarged part that has more than one storey and extends beyond the rear wall (A.2(c)), including where it would be joined to an existing extension (A.2(d)). Article 2(3) land is a conservation area, an area of outstanding natural beauty (National Landscape), an area specified under section 41(3) of the Wildlife and Countryside Act 1981, the Broads, a National Park or a World Heritage Site (Sch 1 Pt 1). There, a two-storey rear extension needs a planning application (council fee £548 for one house), though a single-storey rear extension within 3 m or 4 m can still fall under Class A. See our conservation area check.
Other things that can remove the right
Flats have no Part 1 rights (art 2(1)). A condition on an earlier permission (art 3(4)), an Article 4 direction, or listed status (LBCA 1990 s7) can change the answer. A February 2024 government consultation proposed changes to householder rights, but GOV.UK still says "We are analysing your feedback", so the current limits stand.
What the free check tells you
The free check tests your plot outline against conservation areas and the other article 2(3) designations, Article 4 directions and listed buildings. It tells you whether a two-storey rear extension is ruled out on the data we hold, and the limits to stay within if it is not. It does not take your measurements: the 7 m distance and the eaves heights are for you or your designer to check.
For certainty: a Lawful Development Certificate
A two-storey extension is a big project, so before you start, apply to your council for a Lawful Development Certificate for proposed works (TCPA 1990 s192). The council fee for an extension is £274, half the £548 application fee, and the decision is due within 8 weeks of a valid application. See Lawful Development Certificates and planning fees 2026.